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SNESNESCUBE64

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Blog Entries posted by SNESNESCUBE64

  1. SNESNESCUBE64

    Andromeda SS - Can't Count Correctly

    By SNESNESCUBE64,


    Arcade Repair
    This was a really goofy one that a friend sent me for repair. It's an odd space shooter-type game made by Irem called Andromeda SS. It uses M11 hardware with several mods for sound. Fortunately for me though, the CPU board didn't have many mods.

    The main issue is that it wasn't counting correctly. In Andromeda SS it has a bonus counter on the bottom that counts down. Basically, it starts at 99, but once it got to 95 it would count weirdly. It would count kinda like this: 95->91->90->81->80->71...

    The big thing that I was asked to do was hook my Fluke 9010 to it just to check. I originally wasn't going to be looking into this much due to lack of available time. But I told him if the fluke pointed out something obvious I would try some things.

    Basically, first thing I did was do RAM short tests. Typically if RAM has something wrong it will fail during the short test. I tested both the scratch and video RAM as that is all the CPU can both read and write to. From I read the ROMs just to get the checksums, the goal was to be able to see if it matched what was in MAME. However, before I did the comparisons, I did RAM long tests, which is a more thorough RAM test that the fluke can do. To my suprise the video RAM was would fail about 20 seconds or so into the test.

    So if the video RAM was flakey, it means that things like counts could get messed up. Looking at it, there are four sets of RAM chips.
    Scratch RAM - six 2111 Video RAM - two 2114 Color RAM - eight 2102 Background/stars - three 2102 In my experience, 2114 SRAM ICs can be incredibly problematic. When they start to go they can flat out fail or be inconsistent. So I just went ahead and socketed/replaced them.

    After that, I fired the fluke back up and performed the same RAM long test, this time it succeeded. From there I ran the game with the fluke and saw that it was counting just fine. Glad that worked because I wouldn't have had much of an idea on where to go from here.

  2. SNESNESCUBE64

    Atari Centipede - corrupted graphics

    By SNESNESCUBE64,


    Arcade Repair
    This was probably one of the quickest repairs I've ever had. I got a pile of Atari Centipede boards I needed to test and get up and running, what's nice about that is that I can swap things around quickly.
    First board I looked at had corrupted graphics. The game was running just fine, but the sprites were all wrong. Some were fully corrupted and most were completely wrong.

    So with centipede, it has two 2516/2716 equivalent ROMs for storing the sprite data. They are located at F7 and H/J7. I noticed that one of the ROMs was physically damaged, so I changed that one first and saw improvement. Sprites were no longer glitchy but were wrong. Replacing the second had fixed the rest of the graphics troubles.

    Sometimes it really is that easy, ROMs are not difficult or expensive to replace, so easy and cheap fix. This repair only took about 5 minutes from first seeing it with corrupted graphics to seeing it working perfectly.

     
  3. SNESNESCUBE64

    Atari Centipede - No Boot

    By SNESNESCUBE64,


    Arcade Repair
    Last repair from today's pile of Centipede boards. This one kept on resetting when it loaded the initial mushrooms.

    One thing I noticed is that all the legs on the ROMs were corroded, so first thing I did was clean them using TarnX as the legs were made from silver. Just as a note, the easiest way to tell whether or not the legs are silver are if they turned black from corrosion. Normal EPROM legs will not do this.
    Even after cleaning the legs, the game still would not boot, so the next step was to verify the ROM's contents. The way I do this is by using the ROM identification tool at arcaderestoration.com.

    The way this works is you upload the dumped ROM files and it compares them against what is found in MAME calculating the checksum. It should match up to something assuming the ROM is in MAME.

    All the ROMs matched a counterpart in MAME except for the one at F/H1. From there it was as simple as writing a new ROM. After writing the new ROM, the game booted up just fine!

    Solution: Replace F/H1
     
  4. SNESNESCUBE64

    Atari Centipede - Quiet/Distorted Sound

    By SNESNESCUBE64,


    Arcade Repair
    This isn't going to be as much of a log, but I had a centipede on the bench with really quiet and distorted sound, it ended up just being a bad LM324 preamp at K10. The way I troubleshooted this one was literally by stacking a known good one right on top of the bad one. I did a little video to showcase exactly what I am talking about:
     
    Edit: just to emphasize how common of a failure this is, I worked on 8 centipede boards today, 3 out of the 8 had a bad/failing LM324. It's good to have a large quantity of these things lying around if you repair boards...
  5. SNESNESCUBE64

    B&K 467 CRT Tester/Restorer

    By SNESNESCUBE64,


    Equipment Repair
    This is a bit different than what I normally do, in fact this is the first peice of equipment that uses a vacuum tube in it that I have acually worked on. So for those unfamiliar with the B&K 467, it is a peice lf test equipment meant for analyzing the health of CRT-based displays and if necessary, attempt to "rejuvenate" the tube in order to squeeze a bit more life out of it. It is particularly useful in the arcade world as many of those cabinets still have a well-used CRT in them. It is calible of testing most CRTs as it utilizes a modular approach by using interchangeable sockets.

    When I got it, the tester was in a very well-used state, with the case being held together by duck tape. The first thing I did was add hinges and latches to make the case open and close as it should. What I used was just generic latches and hinges meant for small kitchen cabinets. It turned out very well in this case. I think it looks very nice for this application.

    The next step was to replace the line cord, the original was not in very good shape. It was starting to fray on both the line and neutral wires, because it risked a short, I replaced it before I even powered it up. While I had it dissassembled, I also relfowed the solder joints that were on the board, particularly with the connectors.
    After it was patched up, I was able to finally test it. It powered up fine, and even let me set the heater and G1 voltages. The problems arose when I tried to set the G2 cutoff voltages for each gun. To describe the problem, basically if you turned one knob, all the guns would adjust, which is incorrect as they should adjust individually. After the annoying disassembly, I realized that overall it was simple, but a mess. Thank goodness for the good dissassmbly instructions, which guided me through the process.

    So after reading the service manual and looking at the schematics, I was able to narrow down the points of interest. Since it was a more universal issue, it mostly had to do with the circuit containing the vacuum tube and the multiplexing circuit. 

    The service manual suggests checking a few places in this area, the 12BH7A vacuum tube, transistor Q1, diodes, D1 through D4, capacitors C11 and C12, resistors R41 and R43, and the two integrated circuits involved in the waveform generation. Unfortunately, none of these components tested bad, everything in theory was working. I even brought the tube to a local electronics shop that still had the oldschool tube tester. Afterword, I started just checking the components that were not specifically listed in the service manual as points of interest. To my surprise, the culprit ended up being a few bad resistors that showed no signs of damage. The major one was R70, which was connected to the tube itself was open. Two other resistors, R44 and R37 were also out of spec. After replacing these, I put the thing back together (frustratingly you have to reassemble the whole thing in order to properly test it.

    After everything was said and done, I fired it back up and was finally able to set the cutoff properly and move forward with the other functions. Everything seems to be working great now, I was even able to use it to clean and balance one of my Donkey Kong monitors, tested good afterwords as you can see in the image below. 

    All that is left now for me to do with this tester is to build more adapters, which I will do as I aquire more sockets. I also need to just build one of those universal harnesses in case I can't get the socket.
  6. SNESNESCUBE64
    Symptom: Lower left drop targets not resetting when all three are knocked down.
    Troubleshooting Steps:
    The first thing that I do whenever I deal with a non-functional coil is I check the coil itself. On a pinball machine, it is super easy to do this typically. The first thing you would do is remove the lock bar and playfield glass. Next, be sure to remove the balls themselves. This is an important step, as when you are lifting up the playfield, they can free themselves from the trough, potentially causing damage to the plastics or if you are REALLY unlucky, the back glass. After the balls are removed, lift up the playfield and secure it on the kickstand (or whatever means that particular unit has for doing such. For Black Knight, it has a kickstand so that makes it easy.
    Upon visual inspection of the coil, I could see that it is super burnt, meaning that it was constantly engaged for way too long. You should be able to move the piston that solenoid pushes with your hand under normal circumstances and it should move smoothly. This one however was seized, indicating that the coil or sleeve needed to be replaced. This case was a bit extreme, so the coil is just going to be replaced. This happens for a few reasons: return side of the coil is shorted, the switch telling the mainboard to engage it was stuck, or something in the drive circuit was damaged. The drive transistor is typically the first place I check if there are no visible shorts, as those fail pretty often as they are hard working.

    Looking at the manual, it was really easy to identify which part of the circuit to look at. You can typically find pinball manuals online on websites like ipdb.org. Each manual is different, but manuals by Williams typically were comprehensive. Table 2 and 4 told me the solenoid number (02), what coil to replace it with, and which drive transistors were involved.

     
    With the transistor in question identified, I could easily take a look at the board. The only problem, is that Williams did NOT use silkscreen on the gameboards during this time, so you have to refer to the component layout diagram in the manual. You can also double check the schematics to make sure there wasn't a mistake, as well see the rest of the circuit to inspect.

     
    So now looking at the board, I could see little balls of solder on the cooling mount tab and discoloration, a strong indicator that it got pretty hot. At this point, I was fairly confident that this was the issue. The 2N4401 that drives the drive transistor could also have failed, but that happens a lot less than the drive transistor itself as it is working with a lot less. The 7408 could also fail, but many times you would see multiple coils having issues. So I decided to just replace the drive transistor at Q17 with a TIP102.

    After replacing the drive transistor, the coil performed as it should. In order to avoid excessive coil damage like this, make sure that your solenoid fuse is the correct value (the manual has that information and there is typically a fuse chart in the back box) and if you see or hear a solenoid fire and get stuck, it is a good idea to turn off the game and investigate. Coils are still made but are more expensive than a simple switch adjustment, just replacing the drive transistor or coil sleeve, and fuses are cheap so use the right value.
    Solution: Replace bad solenoid and Q17 (TIP102)
  7. SNESNESCUBE64
    This was an old repair that I did a while back, there was a lot wrong with it, surprisingly all CPU board issues...
    Symptoms: -5V rail was shorting to ground
    Solution: The bypass cap connected to the -5V rail had shorted, needed to be replaced. One thing to note is that several capacitors on this bubble bobble boardset had started leaking, so I ended up replacing all the capacitors with new ones.
    Symptoms: Not booting
    Solution: The game was stuck in a reset loop, it ended up being a bad 6264 RAM chip (the work ram). Game fired up after replacing it.
    Symptoms: Garbled up graphics and Common RAM error

    Solution: The garbled up was an easy one, there were two corrupted EPROMs, reprogrammed accordingly. The common RAM error had me stuck for a while. To make the story short, it ended up being the PAL at IC49 ended up being the cause. Replacing that solved the issue and brought the game to full working order.
  8. SNESNESCUBE64

    Donkey Kong - Distorted Thump Sounds

    By SNESNESCUBE64,


    Arcade Repair
    This is actually a followup to a previous repair log I did on a previously repaired Donkey Kong boardset. Reason being is that last night I decided to run the game overnight to verify that the game will be reliable. Unfortunately when I ran the game this morning, the thumping sound that Donkey Kong was very high pitched, almost like a beep. When I power cycled the game, it was no longer a higher pitched tone, but rather a low distorted tone (closer to the actual thumping noise).
    First thing I did since it was distorted, was I probed around on the area in which a couple transistors mix in this audio. It was only two transistors and a few passive components, so it was quite easy to verify that everything there was working properly. One interesting thing I learned with this, is that if you short the base and emitter of the transistor Q2, it will actually trigger the thumping noise (in this case a very distorted one) to output on the speaker.
    With the mixing circuit verified, it was time to trace the issue back. The way DK generates the thump, is with a series of shift registers that are oscillating amongst themselves. From there the shift register feed into a xor (exclusive or) gate, making a clock that feeds into a counter, whose carry out is the waveform that makes the thump.
    Thump Noise Circuit Snippet

    The first logical step in this circuit is to verify 3J. 3J was giving an output, so potentially it was functioning fine. I went ahead and checked all the clock and all the outputs to verify it, everything looked good here, so the problem had to be farther upstream. This is where I began to question whether or not the clock signal was good. Probing the clock input, it seemed very odd that it was a perfectly consistent square wave. The way you make noise is by providing some sort of variations in the frequency in a square wave. So what I did was double check how it was supposed to be on another DK board. On the good one, the waveform was completely different, which confirmed that the clock input was incorrect.
    Bad Clock at 3J
     
    Good Clock at 3J

    With the clock being incorrect, it was now time to probe around further upstream. Being that the signal was generated by the xor gate a 3K, it was a good idea to probe the inputs. Checking the inputs, I noticed that one input at pin 12 was stuck low. That is a problem as this means that this side will never effect the xor gate. The next step was to set up the logic analyzer to verify 74LS164 serial-in-parallel-out shift registers. With it set up, I noticed that although the shift register at 4K was getting a clock signal that looked correct, it was getting no data as it was pegged low. This makes sense, if the data is constantly low, then it will always output low. So the attention shifted to 5K as the data for 4K was generated by the eighth bit in the register at 5K. Hooking up the logic analyzer, I could see that the shift register was doing its job properly up until bit 6, from there it screws up its own signal and does not shift it as it should, rather it seems it almost imitates the clock.
    Bad 5K Output

    With the issue identified, it was really easy to come to the conclusion that this part was causing the issue and needed to be replaced. With it replaced, I checked it again on the logic analyzer to see if it was indeed the problem. Being that it was now shifting correctly, I could verify that this issue had been fixed.
    Good 5K Output

    After verifying it good with the logic analyzer, I hooked back up the sound amplifier back up to my test harness, and the thump sound was back and sounded exactly as it should. Now all that's left is to run the game for a while to make sure the game runs well. Crazy what one bad chip can do to a circuit like this.

  9. SNESNESCUBE64

    Donkey Kong - garbage on screen

    By SNESNESCUBE64,


    Arcade Repair
    Game - Donkey Kong
    Symptoms - Garbage on screen. It boots to the highscore table, but full of junk. From there it moves to the attract mode but mario falls below where he's supposed to be, game resets, and repeats this process. (Ignore the inverted color in the first picture, I didn't have an inverter board on hand).

    Solution - The board was originally missing stuff and had previous work (it was an 'untested' special on ebay). The previous work looked fine so I could start. I figured the problem to be a memory issue. I initially started on the CPU board, I figured since the game was resetting it was a CPU board. After probing around I I didn't find anything immediate so I moved to the video board. I started by piggybacking known good RAM chips on the board and saw improvement. It turns out that 2114 RAM had gone bad at location 2P. Socketed and replaced, game is now working great.
  10. SNESNESCUBE64

    Donkey Kong - No Boot

    By SNESNESCUBE64,


    Arcade Repair
    So I had gotten some semi-repaired boardsets off KLOV last week. I've been wanting to get another Donkey Kong boardset for a while since I plan on getting a cabinet soon. Both boardsets did not work, both having different errors. When hooked up, it booted to nothing. First thing I noticed was that a bunch of chips had been socketed. None of the sockets were in good shape (one was an old nasty machine pin socket, another was a damaged dual wipe, and there were two terrible single wipe sockets), so they needed to be replaced. After doing such, I finally got a picture on screen.

    Afterwords, I saw that it wasn't booting, so I was able to make use of my recently fixed Fluke 9010a. I used it to run RAM and ROM tests, all the CPU ROMs and CPU RAM tested good. So that meant that something controlling the video board was goofy. I tried writting to the start of the VRAM (Address 7400) and found I was unable to write the data and read it back.

    So I set the fluke to constantly write FF to address 7400 in hopes of trying to figure out where the disconnect was using my logic probe. I found that for some reason, all of the data lines were just floating, occasionally having some activity. This means that the buffer at 6A was not passing the data by. It was getting data in, but it wasn't outputing, implying that it wasn't being enabled, meaning it was stuck in triastate which makes sense for it not to be passing data. After looking at the enable line, it looked as if there was some activity. But after looking at it on my oscilloscope, the line wasn't being pulled low enough in order to enable the buffer. The chip that controls this is a 3 to 8 line decoder (74ls139) at 2A. After replacing it and running the ram check on the VRAM (7400 to 77FF), it passed. From there I ran the game and it booted up.


     
    The game worked just fine. Only problem was the colors of the characters were goofy. They would basically change color half way through being drawn. So this had to be a color selection error since it was being drawn properly otherwise. Basically I landed on 5M, a 2 to 1 multiplexer (74ls257). By this point I had just been measuring the inputs with my oscilloscope just to see if they were there but too low to be recognized, and while checking pin 2 on 5M, it had fixed itself. I had to think about it for a minute as to why this worked. I was looking at it and the ground clip had come off, after the clip came off the signal started acting goofy again. At that point it had all made sense. Inside my scope probe, there is a 22pF capacitor. This acts as a filter to get a better reading on the oscilloscope. By measuring it, I was actually slightly filtering the signal. 
    This can be seen below, I had added a 68pF capacitor as that is what I had on hand. Notice in the first image, there is a lot of wobble. If the wobble gets too high, it is basically tristate, which means mux may not interpret the signal properly.
    Ultimately a small 68pF capacitor fixed the issue.

    No capacitor:

    With 68pF capacitor

     
    After this was done, I now have yet another working Donkey Kong boardset. This one was a bit more challenging than the other nintendo boards that I've worked on. Especially with that wonky signal, I found that on accident ultimately. I'm just glad in the end it worked out.

    If you have any questions, feel free to ask in the comments, or if you are uncomfortable asking it publicly, shoot me a message and I will be more than happy to attempt to answer it.
    Update: chips outputing a noisy signal like that of which I fixed with a small capacitor are an indicator of a failing chip. After taking a look at the schematics again, I found that the noisy signal came from the 74LS245 buffer at 1S, after replacing that, the video board worked perfectly without the capacitor.
  11. SNESNESCUBE64

    Donkey Kong - No Boot/Resetting

    By SNESNESCUBE64,


    Arcade Repair
    Yet another Donkey Kong boardset that boots to garbage. This one was a bit more interesting as there were two main problems with this board. Whenever the game does not boot, I always check the ROMs and make sure that the game can read the ROMs if I can check that. The ROMs all checked out good using my programmer, so now it was time to check to see if the game board could read them. The way I check is by using a Fluke 9010a with a Z80 pod. What this does is it emulates the Z80 CPU and allows me to run troubleshooting, such as ROM and RAM checks. To check the ROMs on Donkey Kong, you are going to need to run checksums on the address range of 0000 to 3FFF. Attached are what the checksums should commonly return, a different rom set will return different values, but these are the most common for this type of board.

    After verifying all of the ROMs and that they could be read with no issue. The next check was to check the CPU RAM. There are six 2114 SRAMs (1kx4), resulting in three pairs of two. The way they work on Donkey Kong is that they are set up in pairs to form a full 8 bit bus since the 2114 only stores words that are 4 bits wide. They are separated into the upper and lower bits, the lower being D0 through D3 and the upper being D4 through D7. Often times when these fail, the data will be messed up for only one. 

    While running through my RAM checks, I found that there were two RAM chips that had actually failed: 3C and 4B. After replacing these, it now passed all of the RAM tests, but it still wasn't booting. It looked like it was actually resetting while trying to display part of the title screen.

    What was weird about it was this is that nothing looked out of place with any of the control signals, so I ended up doing some research and found that the TKG4-14 has a watchdog circuit (I believe that's what it is). One way to disable this for testing is to cut the jumper CR3. To my surprise after cutting the jumper, the game booted up! After probing around, I found that pin 5 was actually floating. It ended up being a problem with C164, that cap had tested open, the watchdog was always activating. After replacing it, the CPU board worked exactly as it should.

     
    One new capacitor and two new RAMs and this game is now back in working order, on to the next DK!

     
      
  12. SNESNESCUBE64
    Symptoms - VERY QUIET audio, was barely audible with my audio amp all the way up
    Solution - There was a single burnt resistor, R13, which was just a 1k ohm resistor. After replacing that and the damaged capacitor that was next to it. The resistor is connected to the 5V rail, so based on the fact that it burned up makes me question whether or not the power rails were swapped around on accident. I got half a hacked harness in the box, so that further supports this theory. 

    Anyway, this one is good to go, remember to hook your harness up right!
  13. SNESNESCUBE64
    So this was a boardset that I got from 8_bit_guerrilla as he no longer needed it. When he bought it, he got it from a seller saying that it had minor sprite issues. I think the seller lied a bit, because it was a bit more than minor. Essentially, the positions of sprites were all goofed up. On top of that, the original braze kit (an old one mind you) also no longer worked.
    The first step I followed was finished converting it back to stock, which was a simple as removing the leftover bodge wires (8_bit already removed most of it). the only thing to note was that Vpp had been cut on the 7C ROM on the video board. This was because the ROM was replaced with a 2732, which is the same pinout, but with an extra address pin where Vpp was for the braze kit mod. Vpp is supposed to be tied high, so I fixed that issue.

    Once the bodge wires were fixed, I hooked up both the CPU and video boards to be greeted with garbage on the screen, no booting. This was simple enough, it turns out ALL of the sockets were nasty and corroded. I ended up replacing each one, that solved the issue, the CPU board was now able to boot just fine. I tested it with a known working video board, and everything worked perfectly. 
    The next step was to test the video board. The issue here is that colors and positions were totally goofed. The first suspect was the ECL RAM. The ECL RAM on Nintendo arcade boards is used for color mainly because these RAMs are incredibly fast, especially for that time. The first one was straight up missing the cap, exposing the die (shown in the bottom picture), I figured that would be a problem, so I replaced it with a known good ECL RAM. That brought back some of the color, but sprites were still messed up. 

    The thing about sprites on DK Jr board, is that they are normally stored in the 2148 static RAMs, but I come to realize that this wasn't the issue. I ended up testing most of the chips in that circuit that could potentially cause an issue like that, but to no avail. So I figured that maybe for some reason, the ECL RAM might be bad, as it controls the color. It made sense as from a logical perspective, the game was running just fine, sprites were internally kept where they were supposed to be. But the thing is color and color position are calculated and done completely separate from the 2148s. And with colors still being messed up, there was a chance that it could have still been it. After replacing it, it brought all the colors back, and everything was positioned where it was supposed to be. EXCELLENT.
    With the game boardset running, I could do a burn in test. This proved to be problematic, as I started having sprite issues again, this time it was a logical problem as sprites were kind of split up. Essentially it was a horizontal position counting error (sorry, I didn't take a picture, didn't think to). It ended up being a 74LS367 driver chip at 1P. This made sense as passed on the horizontal pixel count, eventually ending up at the sprite RAM's address lines. Replacing that fixed this issue, the old chip would just become flaky after warming up.
    One final problem that I encountered was that digital audio was distorted and quiet. This screamed the MB3614 OP-AMP at 7K. These kind of OP-AMPs are a failure point in the circuit. Really, there are only three real points of failure with digital audio. The 8035 MPU that is used to generate the sound (of which I replaced with a NOS one), the DAC that converts it to an analog sound, and the OP-AMP that makes it loud enough to make it to the actually amp in the cabinet. Being it was distorted and not just complete garbage and not working at all, I figured it to be the OP-AMP. I replaced it with a LM324 as that was close enough to the specs of the original. This ended up fixing it.
    After all of that, I now have the boardset working. It was a bit more challenging for me, especially the ECL RAM part as I've never worked with it before. What was nice about this experience as I got to learn a lot about how video is generated on DK and DK Jr boards, which I will take with me to the future as I don't think these are gonna be the last ones I do.

  14. SNESNESCUBE64

    Donkey Kong Jr. - no boot

    By SNESNESCUBE64,


    Arcade Repair
    This was a quick one that I did. I recently got another DK Jr boardset as part of a trade for a working one. To make the long story short, the game wasn't running. 

    The first step whenever you get a game that isn't booting is to check all the control signals such as reset, clock, NMI, Interupt, ect. If any of these are not functioning properly, then you are going to have issues with the game not booting. 
    So I checked all the control signals, everything checked out perfectly, everything except NMI (Non-Maskable Interrupt), which was stuck high when it should be toggling. NMI is a hardware interrupt that is critical to the video and cpu operation. It provides the cue for the CPU to execute code that can only be executed during VBlank, which is part of what triggers the NMI. With this being a serious problem, the first step was to check the flip-flop that controls it, which is at 8F (74ls74). 

    There are 5 signals to worry about on this kind of flip flop, reset, set, clock, and the output. In this scenario, the data in is tied low and the reset is tied high. So the only valid control signals here are the clock (which is derived from VBlank). Checking this with my logic probe showed that it was toggling, meaning that it was probably not the problem. This just leaves the set signal, which was tied low. This is a problem, as for the flip flop's output to change, this needs to go high. 
    The set signal for 8F is generated by a decoder at 5H (74ls259). Looking at all its signals, it looked like all the outputs were stuck high. First thing you check here is the enable, as if the chip is not enabled, then all its outputs will be high. Turns out that the enable was stuck high, meaning that the chip will never be enabled. Looking at how that is generated, I ended up at 1C (74ls138). Looking at its signals, all of its outputs were high. Guess what? This chip was also not being enabled. So looking at the 3 enables, there was one in particular that was stuck high, g2a, this signal is generated by the 74ls139 at 2A. Once again, this chip wasn't being enabled either, but this time it was different. This time, the enable pin was stuck in tristate, meaning that it wasn't high or low, but rather it was stuck at around 1.5V. This signal was produced by an OR gate at 1A. This ended up being a problem, an OR gate chip output should NEVER be in tristate, it should be high or low.

    I checked the other signals on it, everything else looks fine, but its still a problem. After replacing the the 74ls32, the game was able to finally fire up. After playing the game for a bit, it was deemed good to go!


  15. SNESNESCUBE64

    Fluke 9010a - display problems

    By SNESNESCUBE64,


    Equipment Repair
    So for a long time I have been saving up for a Fluke 9010a, an in-circuit debugger for systems that utilize microprocessors such as the 6502, z80, and many others. It is a popular peice of test equipment for folk who do repairs on vintage arcade boards as it is super useful for debugging hardware problems.
    So I had finally won one in an auction, only problem is that it was having display problems.

    problem was that segments were stuck on, which tells me the display tube was good. (At least until I dropped the display module, broke the tube, then ended up replacing the tube with the only close one on ebay, bringing it back to the condition it was before I broke the tube). So I noticed that basically only some of the middle segments were stuck on. In the service manual, it has a chart that shows how the segments are categorized.

    Since all the characters were working, I could guess that the gate controller side of the VFD circuit was working. And being that it was only some of the middle segments, it was on the segment controller.

    Thankfully, the service manual shows that the segments in question are only controlled by two chips: a shift register (U14) and a VFD driver chip (U12). In all reality, it could have been either of these chips, so I socketed both of them with the intent of replacing both. However, I took a closer look at the shift register, being a CMOS chip, I figured it had a higher chance of failure. From there I hooked up the shift register to my logic analyzer to see what it's up to.


    Taking a closer look at the signals in the shift register. We can see that it's clock, strobe, and it's output enable are all toggling as they should, this is fantastic. We could also see that it was getting data input, so that means the microcontroller is feeding it data. Only problem here, is that that the data output, labeled as D_OUT, was not changing, even though that the data input did (as shown in the middle D_IN pulses). This was our problem here. After changing it, all our display segments were working perfectly.

    The overall lesson though, is be careful, I'm still kicking myself for dropping the display module. I got super lucky that I was able to source a replacement. At the end of the day, I was able it working and even decorate it with some stickers of art drawn by a super cool artist here on VGS.


  16. SNESNESCUBE64

    G07 Monitor - Kicked Neck++

    By SNESNESCUBE64,


    Arcade Monitor Repair
    This has been a project I've had for a while. Basically, I had aquired a g07 arcade monitor had it's necked, killing the tube. Being the nature of it, I really wanted to bring this thing back to life. For reference, I've had this project since the end of october, and I just now finally finished it, shows how behind I am...

    So the first step here, find a donor CRT. Compatible 19" tubes are starting to get harder to find. Fortunately, I had a broken tv set with a tube that had high life in the tube according to my CRT tester. I checked the tube that was in the tv set, it was a 510UEB22. Not an ideal replacement for the G07, but it was a tube that used the CR23 pinout and it was the right size, so it was worth a shot. Only problem I forsaw is that the tv set's yoke was slightly off in its readings, but was close enough to where it would work. This was great because I REALLY didn't want to swap the yoke, as it would have been a nightmare to redo the convergence.

    After swapping the tubes, I without hesitation i fired it up. Picture looked alright. Initially I had swapped the wires for the vertical axis, which made it display upside down. That was an easy fix however, as I just needed to switch the Y axis yoke wire.

    There was one problem that I had noticed though. The picture was kind of folding over itself (on the bottom in the picture). This is can be a sign of aged capacitors, unfortunately all the capacitors were original to monitor, which means they absolutely needed to be changed. While I was working on it, I also realized the flyback was original. After hearing horror stories about original flybacks for the G07, I decided to change that as well. 20 or so capacitors and a new flyback later, I was finally able to fire it back up again.

    Firing it up, the picture looks pretty good, could probably use some slight adjustment, but that's ok. It has some slight geometry errors but it won't mattee when a game gets going on it.


    It is kind of a bummer that the original tube was destroyed, but hey, at least I was able to get it replaced. I did keep the CRT's guns as a souvenir though.

  17. SNESNESCUBE64

    G07 Monitor - no picture

    By SNESNESCUBE64,


    Arcade Monitor Repair
    Here was a quick repair I did last night. It was on a G07 arcade monitor that came out of a centipede cabinet. When tested on the bench, I got no picture whatsoever. Looking closely, I heard no high voltage and saw no neck glow. What's nice about the G07, is that it is one of the easiest monitors to work on, it is as simple as unplugging thing the yoke, degauss coil, and anode cup, then remove two screws. Afterwords the chassis will slide right out! This monitor was in pretty good shape, it seemed to be completely untouched, which is fantastic because I didn't have to worry about operator shenanigans. Only real glaring problem was its burn in.

    Just as a note, this is a CRT repair, don't try this at home unless you are comfortable working with high voltages that can really hurt you
    So the first thing to do when you get something like this, is to follow the G07 flowchart, which will give you a lot of good info to follow. First thing to check is the fuses. I could hear the degauss coil charging up when power is applied, so I know the main fuse wasn't blown, the next place to check would be F901. If that fuse blows, then odds are your HOT (Horizontal Output Transistor) or your flyback is toasted. The first thing I checked was the HOT, as that is a bit easier to test. First thing to do when testing the HOT is remove it out of circuit, on the G07 it is as simple as removing the three wires from the large 2sd870 bottle cap transistor near the flyback as well as the capacitor hooked up to it. From there I tested between the base and collector and the emitter and collector. The way you do this is to set your multimeter into diode mode and measure the voltage drop. A good reading should be somewhere between 0.4V and 0.7V. If you are measuring 0, your HOT is no good and it's time to replace it. In my case, I verified that the HOT is probably alright as I didn't measure any dead shorts.

    So since it was probably not the HOT, it was probably the flyback. I just went ahead and just replaced it, as original G07 flybacks tend to have a bad reputation anyway. (New one on top, original on bottom)

    After replacing the flyback (and fuse F901), I fired up the monitor. It worked perfectly. After dialing in the focus and brightness, it looked pretty dang good.

    The only thing left to do now for this guy is change the capacitors, as they all seem to be the originals and are probably near their end of life if not long past. For giggles I decided to check the tube's health just to see how nice it was. Turns out it was a pretty healthy tube!

  18. SNESNESCUBE64

    G07 Monitor flyback issues

    By SNESNESCUBE64,


    Arcade Monitor Repair
    This log is actually a two-for-one as it was for two seperate monitors (I've been in a monitor repairing mood as of late). G07 monitors are my absolute favorites to work on as they tend to be fairly reliable after being serviced. However, they seem to always have issues with their flybacks. To give a brief summary of what the flyback does, it is the transformer on the circuit board of the monitor that generates the high voltage needed to create a the beam that draws to the phosphors as well as other voltages.
    G07 #1 - No Neck Glow/Picture
    This one was actually interesting, I had just recapped the monitor and was testing it out. Fired right up, no smoke or blown out fuses and I could hear the high voltage. However, I got no picture. To my surprise I saw no neck glow on the tube, meaning that it wasn't getting the heater voltage. Interestingly enough, there isn't much in terms of circuitry, the heater voltage is derived from a winding on the flyback itself, from there it goes to some pretty standard components that typically aren't failure points
    The solution here was just to replace the flyback to see if that fixes the issue. New ones are readily available online from various arcade retailers for ~$30 or so. After replacing the flyback, it confirmed that the the winding was open and not making the 6.3V necessary for the heater, meaning that it had failed gracefully without causing other issues.
                        
    G07 #2 - No High Voltage/Blown fuse F901
    This one showed immediate signs of damage. First thing I noticed when I looked at the monitor was that the Ferrite Core on the side of the flyback was broken. This typically means that the flyback violently ruptured, typically due to a short on one of the high voltage windings. To accompany this, fuse F901 was blown out, typically this is an indicator of either a bad horizontal output transistor (HOT) or flyback. Upon examining the flyback, I noticed a large crack that went all the way around the flyback. Upon desoldering the flyback more pieces of the ferrite core had fallen out. So it was pretty obvious that this was probably the culprit.

    After replacing the flyback and testing the HOT for shorts, as well as replacing F901, it was ready to be tested. It fired right up and was ready to go back into service.
     
    Flyback failures are super common for the G07. Typically these failures happen after the monitor is recapped, not quite sure why that is, but I figure it is do to age and high hours. At least the parts for this monitor are still relatively common and can be obtained for cheap. Two flybacks in one day is not unheard of, I'm just glad it didn't require a whole lot of troubleshooting.
  19. SNESNESCUBE64

    Galaga - No Boot and Sound Issues

    By SNESNESCUBE64,


    Arcade Repair
    This Galaga board was a two part issue. Hooking up the board, the game booted to a white screen and zeroes. 

    First step whenever you get some garbage like this is to check the signals on the CPU, make sure there are no stuck signals line reset, NMI, or other critical signals. Everything checked out fine, so the next step in this case is to check the ROMs. Verifying the ROMs on my programmer, I found that all were good except 3N, which wouldn't read anything back, completly dead. After programming a new ROM, the game fired right up! Everything worked fine except for the sounds, many of which just did not sound right. 
    First thing I did in this instance was just shotgun replace the capacitors in the sound amp circuit. They were old and could benefit from being replaced anyway. Testing after the capacitors were replaced showed that there was no change, meaning the problem was somewhere else.
    Looking at the schematic (snippet shown below). It seems that much of the sound in question was generated by a Bipolar PROM whose data is fed into a buffer, through an analog and then sent to the LM324 preamp section. After all that it gets sent to the gameboard's main amplifier and then to the speaker.
    Partial Galaga sound generation circuit:

    Understanding the circuit a bit better, I decided the easiest place to start was with the PROM since I could just swap it with a known good one from my other Galaga boardset. Swapping the PROMs ended up fixing the issue, verifying that the PROM in question was indeed bad. This is rather unfortunate for me as it is a type of chip I currently cannot program, so I will have to source a new one. Just for reference, I made a little video showcasing the sound issue.
    Well, unfortunately the board is in a state in which it needs some PROMs. It has the bad PROM from the previous repair log that I did on a Galaga boardset. My programmers just are not capible of programming those old Bipolar ROMs, one day I will have one that can, but for now the board goes back on the shelf.
  20. SNESNESCUBE64

    Galaga - sprite color issues

    By SNESNESCUBE64,


    Arcade Repair
    Here's a quick one. I wasn't going to do any repairs tonite, but I was pretty bored so I figured I'd start testing a pile of arcade boards. On the bench is a galaga. After cleaning the chip legs of the customs (they are always corroded), I fired up the game. To my suprise it booted up just fine! 
    The problem was that some sprite colors were off, specifically any of them that move such as the ship and the bugs. 


    Thinking about the issue, it dawned upon me that the sprites are controlled by the set of eight 2147 SRAMs. One thing I noticed while probing around on the RAMs, is that the data bits on 6D and 6K were stuck high. Tracing it back, it goes to two 74ls365 buffer chips. Probing those showed that those were functioning as they should. Which means that it was either the PROM at 1C or whatever was controlling it.

    Looking at it with the logic probe, data bit 1 was stuck high, which is not correct for the chip. Swapping it with a known good one brought back all the colors. This is kind of a bummer, as the PROM is a 82S129, which are getting harder to come across. On top of that, I don't even have a way to program them currently.

     
    One more thing, I attempted to do a youtube video on this! Give me some feedback!
     
  21. SNESNESCUBE64
    This entry is meant for simple fixes that aren't worth going in-depth about the repair. It will be updated periodically to add new entries. I only have one to start but should have more later.
    Date: June 12th, 2023
    Game: VS Super Mario Bros
    Symptoms: Low scratchy sound on sub side
    Solution: replaced bad LM3900 at 3N
    Date: September 4th, 2023
    Game: VS Super Mario Bros
    Symptoms: monitor (20ez) experiencing weird issues, small screen and low/unadjustable B+.
    Solution: replaced bad flyback
    Date: September 23rd, 2023
    Game: NFL Blitz 2000
    Symptoms: Random game resets
    Solution: Reseated video card, adjusted voltage to 5V
    Date: December 2nd, 2023
    Game: Ms. Pacman
    Symptoms: Random game resets when the game warms up.
    Solution: repaired damage game board card edge. HASL tarnishing made a poor connection that resulted in it getting burnt
    Date: December 10th, 2023
    Game: Crusin USA
    Symptoms: Game not holding calibration
    Solution: Replaced battery.
    Date: December 16th, 2023
    Game: Ms. Pacman
    Symptoms: No boot, loud humming noise
    Solution: Bad game board fuse block/blown out incorrect fuses.
    Date: December 16th, 2023
    Game: Punch-out
    Symptoms: Game not freezing on the title screen
    Solution: Reseated program ROMs on the game board.
  22. SNESNESCUBE64
    The purpose of this is to put logs that I don't think need a proper writeup. It should be updated periodically.
    Date: November 26th, 2021
    Game: Williams Earthshaker
    Symptoms: Left flippers not working, fuse F6 popping after holding down left flipper button
    Solution: End of stroke switch for upper flipper was not aligned and disabling one of the windings on the flipper coil. Adjusting it fixed the issue.
    Date: June 12th, 2023
    Game: Demolition Man
    Symptoms: garbage on lower half of the display regardless of what DMD unit I use.
    Solution: Bad 6264 (don't remember the designator) on the display driver board.
    Date: July 8th, 2023
    Game: Gottlieb Buck Rogers Pinball
    Symptoms: no displays despite repro boardset being in the unit
    Troubleshooting steps: Noticed HV light for the displays was out. Checking the fuse, I could see that it was out. Replaced fuse, still popped once. Checked harness connections and one of the pins was pushed in. Replaced pushed pin and fuse didn't pop.
    Solution: replaced display fuse due to bad harness connections and replaced probable cause for popped fuse.
    Date: September 9th, 2023
    Game: Bally Strikes & Spares
    Symptoms: Sticking Flippers
    Solution: Used oil in the coils, that is a no-no. Cleaned up oil and replaced sleeves.
    Date: September 23th, 2023
    Game: Williams Terminator 2: Judgement Day
    Symptoms: Cannon not homing, missing some General Illumination
    Solution: Cannon not homing issue resolved by re-aligned the switch. General illumination, like with many games of this time, had burnt connectors that needed replacement.
    Date: November 18th, 2023
    Game: Rocky and Bullwinkle
    Symptoms: Right Flipper not working
    Solution: Bushing that held the piston to the rest of the flipper assembly no longer held the link. So the piston wouldn't actually flip the flipper
    Date: December 2nd, 2023
    Game: Williams Gorgar
    Symptoms: Both flippers weak
    Solution: End of stroke switches were not very well adjusted. Adjusting them properly increased the flipper's power to acceptable levels.
    Date: December 9th, 2023
    Game: Williams Black Out
    Symptoms: Player 1 score display flickering
    Solution: Display tube was gassing. Replacing the tube solved the issue.
    Date: December 9th, 2023
    Game: Williams Twilight Zone
    Symptoms: Balls sometimes getting lost in the gumball machine area
    Solution: This was a goofy one. It ended up being a combination of slightly dirty optos and the fact that the far left trough switch had it's actuator replaced with a home made one. The problem was is that it would sometimes hold up the left trough switch so that it wouldn't register. I believe that's where the ball becoming lost came into play but I am not sure. It worked after all of that.
    Date: December 10th, 2023
    Game: Bally Bobby Orr pinball
    Symptoms: Something was just off about the lights. They weren't making sense
    Solution: One of the light driver connectors was offset by one pin, meaning that the wrong things were lighting up.
    Date: December 10th, 2023
    Game: Bally Popeye Saves the Earth
    Symptoms: Bottom right flipper not working
    Solution: Flipper fuse blown for bottom right flipper on driver board. Cause of fault was because the end of stroke switches for the flippers were trashed.
    Date: December 17th, 2023
    Game: Williams Flash
    Symptoms: Game not starting
    Solution: This was a really weird one. It was struggling to recognize switches with column one. Every time you would hit any switch in that column, it would trigger every switch in the row. So the game wouldn't start unless you held down the start button as a result. The solution ended up being to replace the 13N10L at Q81 (Rottendog board) with an IRL540 as the 13N10L was no longer manufactured and the IRL540 is what I had on hand.
  23. SNESNESCUBE64

    Gyruss - No Moving Sprites

    By SNESNESCUBE64,


    Arcade Repair
    First time that I've ever worked on a Gyruss. I have to say, the fact that it had any custom ICs at all kind of intimidated me a little bit. I am not the best when it comes to video issues, but is something I am working on getting better. But anyway, this was a pretty straightforward repair. So the problem at hand was that there were no moving sprites at all. Text would appear, but nothing that moved.

    This is great because it really helps narrow down the circuit. After doing a bit of research online, I found out that there was actually a test rom, which ended up making the repair even easier. What was nice about this, is that it was only adding one additional ROM in an unpopulated socket at J14. After burning the ROM and populating it, it showed that RAM 17C, all the between 11A and 14A, and the ROM at 19E was bad.

    This is a bit suspicious, because that implies that nothing is working at all with the sprite engine, you would think something would be working. Looking at the schematic, all the data gets sent from the main Z80 CPU to a Konami 501 custom IC, then through a buffer to the 17C RAM and beyond. Here's the problem, I don't have an easy way to verify the 501 is working other than checking it's signals. Everything looked fine as far as I can tell with the outputs of that, so I shifted focus to buffer at 13E (a 74ls245). Looking at the signals on my oscilloscope, I could see that it was getting all the signals but a few of the outputs were stuck low. That was awfully suspicious as it really should be toggling.

    After socketing and replacing 13E, the moving sprites were all back!  Great to know that it was the issue tying everything up. I've never played Gyruss before, it was really fun and I wouldn't mind owning one of these cabinets in the future.


  24. SNESNESCUBE64

    Hantarex MTC-9000 - No picture/heater

    By SNESNESCUBE64,


    Arcade Monitor Repair
    So I recently picked up a Hantrarex MTC-9000 9" (manual says it's 10", but it's definitely a 9" tube) CRT. Initially, the tube had a lot of gunk, a chip on the face of it (not really visible in the pictures), and did not work initially. This thing was used most likely in a poker machine based on the burn on the screen. I love little CRTs like this, they make excellent test monitors and I think I am going to use it for a future project.
    Just as a general disclaimer, CRTs are very dangerous to work on due to the high voltages they rely on for operation. Do not work on them if you are not comfortable with the non-zero chance of serious injury or death that can be caused through mishandling of this old technology. The content in this entry is NOT a guide on how to work on these, but just a log of what I did to get it going.
    So to touch on it not working, I noticed that there was no neck glow, indicating that the heater was out. This is one of a few things: the flyback could is bad and isn't making the heater voltage, there is a disconnect somewhere along the line and the heater line was cut, or something in the circuit between the flyback and the tube itself is driving down the voltage for the heater. Without the heater, the CRT cannot operate, as it relies on the heated cathode to make the beam that activates the phosphors. As shown in the picture below, this is what it could look like with no heater.

    The first thing I typically do on a CRT is inspect it for damage. This could be burnt components, holes, blown fuses, missing components, bad solder joints, ect. After a quick inspection, I noticed that a few capacitors were actually bulging out the top. Not surprising at all, most arcade monitors are high hour and these electrolytic capacitors have long exceeded their life. What was really interesting is that the main filter capacitor was actually bulging as well, I've never seen one with damage like that before.

    Fortunately, I had most of the capacitors on hand, so I just replaced every single electrolytic capacitor on the board (except for one 22uF rated for 200V, I didn't have that one). Typically this kind of thing is the first thing that I do in the troubleshooting process of working on any arcade monitor since bad capacitors are such a big problem with them. If you do decide to work on such, just remember to use higher quality capacitors that are rated for longer life, not just some junk you buy on amazon. Also try to make sure you buy such components from reputable dealers, they are even faking capacitors these days!
    Anyway, the monitor fired right up after replacing the capacitors. It still needs some fine tuning and there's a weird issue where the bottom is beginning to collapse. So I will have to investigate further with this one. I also wanna look into swapping the tube with one out of a consumer TV that I have lying around due to the damage on the face of the tueb, but that's an experiment for another day. Overall it has a pretty alright looking image.

  25. SNESNESCUBE64

    Happ SE-M21C - Horizontal Jitters

    By SNESNESCUBE64,


    Arcade Monitor Repair
    So this was a quick one. I got a monitor about a month ago as just a tube and chassis, as the original owner wanted to keep the frame. I assembled a new frame out of the sides of what I believe was the sides of a WG19K4900 and the base of a G07. 

    After it was all assembled again, I jst needed to test it. Looking at the screen, it was obvious that it had a case of the jitters. I also realized I plugged the yoke in the flipped image plug. 

    After looking closly at it, I noticed that it was only being jittery in a horizontal position, meaning that it had to do with the horizontal sync or horizontal deflection.

    It ended up being C327 right by the flyback. Notice the top is kind of bulging.

    After replacing it, the monitor is looking pretty good. Its a low hour tube with only a bit of burn. A very nice monitor altogether. All that is left is to replace the rest of the capacitors as it is probably ready for it.
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