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SNESNESCUBE64

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Blog Entries posted by SNESNESCUBE64

  1. SNESNESCUBE64
    On the bench today was a Space Invaders Deluxe that I had grabbed off the pile. This one had unfortunately been a parts unit, as someone had taken several parts off the board, probably to fix another Space Invaders board. It was also pretty dirty, so I had to give it a bath.

    After washing the board, my first thing was to attend to the missing parts. It was missing a 9316 (Really a 74161 counter), a 74ls04, and an Intel 3245. The intel 3245 has become a bit more difficult to get a hold of as it was discontinued quite some time ago. So this was actually an opportunity to try to use a Soviet equivalent, which could be obtained for much cheaper because there is more NOS of that left behind. For this I used the K170AP4. 

    Another part that I noticed was missing was the 180pF tuning capacitor that was used to help the crystal oscillate. Unfortunately, I did not have that particular value available. I did however, have a bunch of 56pF capacitors. You can add capacitance by putting capacitors in parallel, so I solder three of them to leads and soldered them onto the board to get 168pF, which is probably close enough.

    After replacing all the missing parts, I found that the game had a dead short on the 12V rail, which is obviously no good. One way to kind of narrow down a short like this is to utilize your multimeter if it is sensitive enough. The closer you get to the short, the lower the resistance will be. First place I checked was the tantalum capacitors, as those have a tendency to short out. It ended up being one of the tantalums by the RAM (shown below). I removed it and replaced it with an electrolytic that I had since I don't stock tantalums.

    After the power situation was taken care of, I hooked it up to find that it booted to garbage. First thing I did was reseat the ROMs and the CPU as midway loved to use bad single wipe sockets.

    After reseating the chips, the game fired right up and worked as it was supposed to, another board back from the dead! It's always a shame to see people use these things for parts. Sometimes it's difficult, especially with custom chips and whatnot.

  2. 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
     
  3. 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...
  4. 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.

     
  5. SNESNESCUBE64

    Sanyo 20EZ Chasis - Burning up R471

    By SNESNESCUBE64,


    Arcade Monitor Repair
    Symptoms: 20EZ losing high voltage and is burning up the resistor R471 and was blowing the 300mA fuse.
    Solution: replaced the burnt resistor, checked the HOT to make sure that was still good. HOT tested bad, so replaced with a NTE89. Fired it back up again, same results. Afterwords I swapped the flyback as that can cause the same issues (and I had one off a working chassis on hand), this solved the issue. Chassis is now working just fine and is ready to roll again.
  6. SNESNESCUBE64

    WG U5000 Monitor - Vertical Collapse

    By SNESNESCUBE64,


    Arcade Monitor Repair
    The U2000/U5000/K7*00 series of monitors are some of my least favorite monitors to work on. They produce a nice image when working, but that's the tough one, they have a lot of flaws. For example, they drive the neck transistors really hard, causing them to get really hot and singe the neck board, which makes it a nightmare to replace the transistors because the traces pull right up. It also has a pretty flawed design with the vertical deflection circuit. The way it derives the voltage for the the 30V rail is from a winding on the flyback, however the problem is that sometimes that voltage gets too high and goes out of spec, burning up the transistor and sometimes components on the way.
    That where the problem with this chassis comes into play, it shows a classic case of vertical deflection failure.

    The first thing I did was replace all the electrolytic capacitors (all arcade monitors can benefit from a quality recap). I noticed that some of the capacitors were bulging out, which could imply failure or close future failure. Unfortunately, replacing the capacitors did not fix the issue at hand.
    After that, I checked the 30V rail, there is a super convenient test point right near the vertical deflection IC. When tested, it showed that it was receiving no power. Great, this narrows it down to R303, D302, or the flyback.

    First thing I did was check the diode since that was next in line, it tested as if it was a dead short (I could even see damage where it got hot), so it needed to be replaced. It is a cheap 1N4937 diode that I was able to obtain locally. While I had it apart, I also checked R303, and that had drifted far out of spec, so that needed to be replaced with a 2 watt 1.2 ohm resistor. I didn't have that on hand, so two 2.7 ohm resistors would be close enough for this. I made sure to raise these components up a little bit so that way if they go bad in the future it won't singe the board. For some reason it also had an extra resistor after the diode, it didn't really make sense and didn't belong anywhere in the circuit. The IC in the picture was just an extra deflection IC because I was about to replace that next.
     


    After replacing them, we finally had vertical deflection, and it was looking pretty nice. I also did some preventative maintenance such as replace R111, as that it looked like it got super hot as the coating was flakey. 

  7. 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.

  8. 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.
  9. 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!

  10. 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.

  11. 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.
  12. SNESNESCUBE64

    Vision Pro MTG-1901 - No High Voltage

    By SNESNESCUBE64,


    Arcade Monitor Repair
    Quick fix on a monitor I picked up recently. When I got it, it would not power up fully. I noticed that I could hear chatter when I gave it a video signal, but ultimately got no neck glow (heater voltage) and I didn't hear any high voltage, so a serious power issue was happening.
    Upon closer examination, I noticed there were a couple capacitors that had bulged at the top, and that a transistor had gotten very hot, enough to singe the board.

    After replacing the two capacitors that were bulging and the burnt transistor, the monitor fired up just fine. While I was working on it, I had also decided to replace the rest of the capacitors.
    I was able to use a new piece of equipment to display test patterns, a Sencore CM2000. I had picked it up this past week as it could help test flybacks and could make test patterns. Because it was a bench unit, it was more ideal for burn in tests as it didn't rely on a battery like the other test pattern generator.


    Anyway, yet another monitor up and running. This one looks alright, has some burn, but no big deal.
  13. SNESNESCUBE64
    This was a repair I was super excited to do. For some background, right now I am in the process of restoring an original Nintendo Radarscope arcade cabinet. The cabinet is in super nice shape but was missing several things.
    Anyway, when I got it last night, I excitedly had to wait an hour for the boardset to warm up as it had been sitting outside in the fridged cold. When I first hooked it up, the game did not boot properly, only showing upside down 2s. 

    The first thing I did to troubleshoot the board was check the sockets. On these earlier nintendo boards, they sometimes used these terrible Texas Instruments tension sockets. They wear out over time and weren't making good contact with the pins after 40 years of service.

    Before I replaced them, I pulled each chip, verified the rom to be good using ROMident (an online tool for comparing ROMs to what is in MAME). All ROMs verified good except the CPU ROMs which did not compare with anything online interestingly enough. With the ROMs checked, I sprayed some contact cleaner into the sockets just to see if I could get some more life out of the boards. The game did indeed start working. Problem was that there were graphics issues.

    First things first, you may have noticed that the image is slightly shifted to the left. On old Nintendo arcade boards such as Donkey Kong, Mario Bros, Donkey Kong Jr, and this one, Nintendo used two potentiometers on the game board to adjust position. These are always crusty or are broken and I always replace them with new Piher PT15s.

    Next step was to start replacing sockets. Since we saw inprovement when I reseated the ROMs on the video board, I decided to start replacing the sockets. Unfortunately, 4 sockets in I ran out. Fortunately though, replacing these sockets fixed the video troubles.
    Now I was ready to test it with audio. Fortunately most of the analog sounds were there, but I was missing digital and one of the analog sound effects. On the soundboard I noticed two things: there were some capacitors that had begun leaking and there was some weird Alkaline-like corrosion on the 556 timer. Both of these problems could effect the soundboard's ability to produce the missing sounds.


    I ended up putting a socket where the 556 timer was and put a new one in it's place. I also replaced the capacitors that were leaking and ordered capacitors for the rest of the board just to bulletproof it.
    After everything was said and done, the game was working and is super cool. I feel like Radarscope is a bit of an underated game, it has nice sound effects and the perspective is unique. It feels like a hybrid between Galaga and Juno First, both really fun games. I can't wait to get the cabinet finished so I can play it for real. 
  14. SNESNESCUBE64
    It's been a while since I did an actual board repair, but this was a cool one. So I was testing a midway space invaders deluxe and noticed that there were whole lines in which there were no pixel data for all sprites. There would actually be other graphics glitches where lines would just appear randomly. 

    Since the game actually booted, I went ahead and burned myself a copy of the space invaders deluxe V1.3 test rom. This is where having some 28C16 EEPROMs around is super useful, I don't like using them for longevity, but they are excellent for testing like this. I figured this would have been a RAM issue, but the RAM tested good according to the test ROM, so it was elsewhere. Instead it failed on the shifter test. Unfortunately, the numbers on it didn't really give me that much insight.

    Stumped, I immediately reached out to some people who were more familiar with these boards, they suggested that it may actually be the custom chip on the sound board. Fortunately, I had access to another boardset that was known good, so I was able to swap the chips, unfortunately I had gotten the same thing, so it was one of the supporting chips.
    My solution for this was to pull all the chips directly involved with the custom, so the 74153s and the 7442. I typically don't like the idea of pulling this many chips out of circuit, but since I had everything on hand, I felt this would be the easiest way to test it. The idea here was that I can swap them out with known good chips, finding out which ones were good and which were bad.

     
    Fortunately, the chip causing the error ended up being one of the 74153s, I believe it was at A3 on the sound board, although since I pulled them all out at the same time, there's a chance I made a mistake there. But I was able to replicate the graphics glitches when I put it back into A3. 
  15. SNESNESCUBE64

    Track & Field - Running forever

    By SNESNESCUBE64,


    Arcade Repair
    Here was a fun one, several months ago I worked on a track & field pcb that was having some werid issues. The first issue was that the game refused to boot. What this ended up being was a bad interconnect ribbon cable. Easy enough fix.
    The second issue was that the game would actually run forever on the 100m. Typically it is supposed to end at some point, however in this case the runners just kept on going, going to a black screen until it timed out. This was a quick fix, the problem was actually a bad ROM at 5A (I think that was what it was, I don't quite remember because it has been a really long time since I did this fix).


    Glad it was a pretty quick fix, ROMs are one of the easier things to diagnose if you have a programmer. A quick reprogramming of the ROM completely solved the issue and the game worked as it was supposed to.
  16. SNESNESCUBE64
    Something a bit different from the usual arcade repairs, recently I picked up a Street Fighter 2 pinball machine (my first pin). It was a wild ride fixing up that, but that's a writeup for another day. As the title states, the big problem at hand was that the table was not putting out any valid sound, there was buzzing but none of Guile's theme or whatnot. 
    So in Street Fighter 2, it utilized the Gottlieb System 3 boardset. This utilized two different sound boards, a large main sound board and a smaller auxiliary sound board. The main board was the one running the show, while the auxiliary sound board handled samples (such as voice I think). The main board itself can even be split up into two different sections, a Y section and a D section, each have their own RAM and ROM. Unfortunately I am not all to familiar with the inner workings here, I just know that one section does the talking with the Aux board and one just makes sound. 

    On to the troubleshooting! One thing to note is that when these boards boot up, they both make a beep noise to signify that both boards booted. They also each have LEDs to signal that they are both operating properly. In it's initial state, I would only hear one beep, meaning that not everything booted. I also noticed that the mainboard LED was stuck on and the aux board LED was stuck off. When I would start the game, it would just buzz at me, sounding like it was just resetting. The buzzing was also a good indicator that the sound amp was working, because otherwise I wouldn't hear anything out of the speakers. The way I attacked this issue was by running through Marco from Pinside's test ROMs. These are excellent tools for troubleshooting System 3 boardsets and were critical to fixing this. The test was always getting hung up during the RAM test for the Y section of the main sound board. After replacing it (it was just a 6116 RAM), both sound boards fired right up and I was hearing the game!

    Now the game is running and has been a blast! Sorry there wasn't as much explanation with this repair, truth is that I don't really know a lot about these because I didn't have to deep dive into it, the test ROMs did all the work for me. There is an EXCELLENT video on how to use the test ROMs, I linked it to the bottom if you want to see the process in action. Funny enough, it was the same failed chip in the video as what I experienced.

     
    Cool video on how to use the test program:
     
  17. 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.
  18. 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.

  19. 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.

  20. 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.
  21. SNESNESCUBE64

    Popeye - Bad CPU

    By SNESNESCUBE64,


    Arcade Repair
    This one was probably one of the quickest fixes I've done. I ordered a Nintendo Popeye board as I saw it rather cheap. I got it, hooked it up, and got no boot.

    First thing I do in games that don't boot like this is reseat all the chips and swap the CPU (if I can easily do that) with a known good one. In this case, I only reseated the ROM chips on the CPU board and replaced the Z80 with one of my new old stock ones I bought recently. After doing such, it booted right up!

    Turns out the Z80 itself was bad, luckily I have several on hand, so it was a quick fix.
  22. 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!


  23. 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!
     
  24. 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.


  25. SNESNESCUBE64

    Pac Gal (Pacman Board Hack) - Video Mess

    By SNESNESCUBE64,


    Arcade Repair
    Here was a quick repair that I did this morning. About a year and a half ago I bought a pacman board that had been hacked to run a version of Ms.Pacaman without the auxiliary board. This was done by adding two extra ROMs and modifying the code a bit. As well as running the additional lines for different enables and cutting a trace so it could address the two extra ROM chips as shown in the bottom two pictures.
    So I hooked it up for the first time the other day, and saw that there were graphics glitches. There's not a whole lot to say about it, it's just not playable this way.

    I made the ultimate decision that this hack wasn't worth keeping and could have potentially been a problem with the ROM chips. So instead of debugging it, I pulled the hack ROMs, put an original pacman ROM set in, and undid the wiring hack. This ended up solving my issue altogether.

    What's nice is now I have a bunch of extra 2532 EPROM chips I can use in future projects. I was also sure to dump the ROMs that were there. I'm gonna try to get it to run in MAME at some point just to see if it was the ROMs themselves or just dirty sockets.
     
    Just as a note for those reading these, if you have any suggestions for me to improve these, feel free to post them. I enjoy writing these little repair logs and if I could make them better, that would be neat.
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