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SNESNESCUBE64

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Blog Entries posted by SNESNESCUBE64

  1. 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)
  2. 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.
  3. SNESNESCUBE64
    This was a quick fix as I've seen this issue before. So I was working on a Data East Laser war pinball machine, and some of the flashers were stuck on. This pinball machine just had all of its bulbs replaced with LEDs, so realistically there shouldn't have been a problem. There were also several stuck on so it was more than just a bad socket or a wiring issue. I identified the bulbs as the following:

     
    Flashers are driven by the solenoid circuits, so it seemed odd that the flashers were for solenoid drivers 6, 7, and 8. Looking at the schematic, I could see that the ones in question all had a warming resistor. What a warming resistor does is that it provides a current to a bulb that is less than what is necessary for it to glow. The idea is that it makes it a little bit quicker to warm up and flash than it would be from a cold start. This can be represented by the highlighted resistors below:

    LED bulbs do not need these warming resistors as they require not only a lower amount of current to flash but because they are LED they turn on much faster. Not even all the flashers have these warming resistors as I pointed out. 
    The solution here was literally to just remove the 660 ohm resistors from circuit. After removing them, they turned off as they should and even flashed as they should.
  4. SNESNESCUBE64

    Wii U kiosk Monitor - Audio Issues

    By SNESNESCUBE64,


    Kiosk Repair
    This is something a bit different that I did a couple months ago. I'll start off by saying the Wii U Kiosk owner should consider doing this fix to their monitor. It is cheap and easy to do if you have any experience with a soldering iron. The monitor is fairly easy to pull out and dissassemble.

    As an overview, there are three boards, a logic board, a power supply, and a backlight board. I theorized that it was just cheap capacitors as I still heard a buzz coming out of the speakers. Because there was a buzz, I figured that the audio amp was fine.

    I started out by making a cap kit. Most of the caps were cheap, I ended up replacing all of them except for one of them on the logic board, of which I mistaken it for another value. Most of the caps were mediocre in quality, brands like Chong. 

    The replacement went really quickly. Ultimately it ended up bringing the audio back. It turns out the sound quality isn't actually all too good. I might look into replacement audio amps and whatnot to try to reduce the noise. That said, I believe the issue was on the logic board, but it could have been elsewhere since I just shotgunned all the parts. With that in mind, all the power supply and backlight board are actually off-the-shelf PCBs that you can buy on ebay. The only thing that is proprietary is the logic board, which was made by Lynx. 
    Attached is the Excel file I used, it is not complete because of the previously mentioned capacitor being the wrong value, I apologize for that. I would take this list as-is, as mine may be different than yours ultimately.
     
    Wii U Kiosk monitor.xlsx
  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

    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.

  7. 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. 
  8. 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!

  9. 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.
  10. SNESNESCUBE64

    Nintendo Helifire - Game Not Booting

    By SNESNESCUBE64,


    Arcade Repair
    I recently picked up a Nintendo Helifire cocktail table and been having a blast bringing it up. There was one main problem though: the original CPU board wasn't working.

     
    With this though, I was able to cheat because I knew it was a problem on the CPU board. Reason being that I had an extra, but I wanted this one working. The first thing I always do when working on a game that isn't booting is check the ROM data. ROM corruption is a very common issue with arcade games due to their use of EPROMs. Unfortunately, these use 2708 EPROMs. Problem is that none of my programmers can really read these due to them being goofball tri-voltage chips. My solution was just to replace all of them with chips that I can program. What I did was make an adapter board that combines a pair of eproms into one. This reduces the chip count and I was able to program my free play mod onto it as a result. It also assisted me in this repair as it garunteed that I had good ROMs.

    Testing with the new ROMs, I still was getting no boot. One thing I like to do with games that utilize 4116 tri-voltage DRAMs is to socket them. They are very high failure compared to other RAMs, so having them socketed on my games is nice. One thing I did find is that several of these RAMs were faulty. I decided to replace the entire bank of 8 to ensure the timings were all the same. Trying out the game, it still wasn't booting!
    One thing I like doing is checking all the signals coming in and out of the CPU, in this case an 8080. Everything looked fairly normal on the 8080, so I moved to the address buffers since it's an easy thing to check. On Space Fever/Helifire boards they are buffered using 74LS08 AND gate chips. One input is always tied high for each gate, so they just act as a passthrough.

    To my suprise, A8 was stuck low despite having a pulsing input.
    Input:

    Output:

    This is a very obvious problem, either the AND gate there was faulty or something in circuit was pulling A8 low. I went ahead and simply replaced the 74LS08. This chip was what was holding the board back. With a new one it now boots as it should.

  11. 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.
  12. 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.
  13. 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:
     
  14. SNESNESCUBE64
    This was probably one of the nastier 20EZs I've worked on. I don't know what this thing's past life was but it was pretty rusty and coated in dirt.



    Regardless of how dirty it was, it will clean up fine. The problem is that the picture was screwed up. It was dim in and had partial vertical collapse. You can even see some waving.

    One thing that is super common on 20EZs is that the electrolytic capacitors go bad. This is especially common with the higher voltage (160V) capacitors. Typically the burst on the bottom like these. When they go bad they can cause brightness and deflection issues in my experience. Just replacing the capacitors will fix a lot of these issues.


    After a good wash and a recap, the monitor was back to working like it uses to back in the day. Lots of times with these it just needs new capacitors.

  15. SNESNESCUBE64

    Vision Pro MTG-2901 - DOA/clicking

    By SNESNESCUBE64,


    Arcade Monitor Repair
    Monitor: Vision Pro MTG-2901
    Symptoms: Completely dead, clicking when powered on
    Troubleshooting steps:
    Like with any monitor, the first thing I do is make a capacitor kit and replace all the capacitors on the chassis. Arcade monitors work long hours and have exceeded their life in many cases. This is especially important with these Happ and Vision Pro monitors, of which have terrible capacitors. Replacing the capacitors in this instance had no real effect on the issue.
    Upon inspection, I noticed that R812 got hot, although it tested good. It is involved in driving the switch mode power supply (SMPS). Looking at the circuit, it is involved with Q801, a 2SC2073 used in driving the SMPS. It looked like that got hot as well.


    It's safe to say, if this isn't working, the SMPS won't be able to operate correctly. Replacing it ended up solving the issue, I also replaced the resistor because I didn't want to return this with a burnt resistor.

    Solution: Replaced Q801 (2SC2073) and R812 (68ohm 1/2W)
  16. SNESNESCUBE64
    This was a neat one because I have not encountered a soundboard issue like this one before. In my short experience with Williams sound boards for games like stargate and joust, they have been an "all or nothing" kind of deal. This one however was missing sounds.

    To troubleshoot this one, I did a few things. When I booted the game up I pressed the test button on the soundboard, it should play game sounds in general, but this just played tones. What this told me was that the CPU, DAC (probably) and amplifier area was working on this board. My guess immediately turned to the EPROM or 6810 Bipolar RAM. I started with the EPROM, what I did was that was dump the ROM and validate it with ROMIdent. The ROM checked out just fine. From there, I decided to test and socket the 6810 since I have had the worst luck with RAM ICs this year and I was replacing the sockets for the ROM and CPU anyway. Using my ABI Chipmaster, I verified that the RAM was indeed failing. After putting a new one in and testing the sound board again, it was working as it should.
    I did a little video demonstrating what I was hearing since sound is not the easiest thing to describe:
     
  17. SNESNESCUBE64
    On my bench (technically the trashcan next to my Helifire table) was Nintendo Space Firebird. This one was specifically the Gremlin license but they are the same game for the most part. The problem with this one is that some sprites are garbled or missing.



    This ended up being one of the quickest repairs I have done. It probably took longer to hook up the board. The problem chip ended up being the second chip I did a spot check on: the 74ls00 at 3D. Probing the chip, I noticed that it had good inputs.

    However, it had floating outputs:

    Stacking a new chip on it fixed my graphics. That was ultimately the problematic chip. Pulling it and testing it on my chipmaster shower it to be bad.


    Fully replacing the chip solved my graphics issue.



  18. SNESNESCUBE64

    Tektronix 2232 Oscilloscope - CRT won't focus

    By SNESNESCUBE64,


    Equipment Repair
    I have been using this scope for quite some time now and it has served me well. It is my go to for quick troubleshooting as it is quick and easy to setup compared to the scope functionality of my logic analyzer's scope. So you can imagine that I was a bit bummed out when I started having issues. Fortunately this one was a simple repair.
    The CRT would not focus all the way. Basically, I would have trace and text if I turned it on, but it was blurry. Typically, it would be simple in the sense that you only have to adjust focus on with the adjustment knob. However, even turned all the way it wasn't quite working the way I needed it to.

     
    The first thing I did was look at the schematics for the CRT section. Fortunately the service manuals for a lot of these old Tektronix scopes are available online for free. So finding the area of interest was super straight forward. The way it works is that the supply for focus is about 2000V, the focus adjustment basically just divides that voltage down just a little bit to tune the CRT. From there it seems that the rest is biased using several 510k resistors in series. 

     
    With the knowledge of how focus voltage is attained, I tested all the CRT voltages. Everything seemed to be there, including the 2000V supply. Next thing I checked was that row of resistors. To my surprise, R888 (A1R888) was testing as open. That is an obvious problem so I went ahead and disassembled the rest of the scope and replaced the resistor. Unfortunately I didn't have 1/2W 510k resistors on hand, so I used a 1/2W 470k resistor since it would still have been in the 5% tolerance range anyway. That fixed it, I now can focus to a nice sharp image.


     
    Crazy what one little resistor can do.
  19. SNESNESCUBE64

    Laser War Pinball - Random Resetting

    By SNESNESCUBE64,


    Pinball Repair
    Symptoms
    Random reset, sometimes resetting rapidly

    Solution Steps
    Looking at the schematics, reset is controlled using a Power On Reset (POR) IC. Basically how it works is that it sends a reset pulse to the CPU whenever a threshold voltage is reached, somewhere in the 4V range. With that knowledge, I had to monitor the reset line.

    In this image, the reset line is yellow and the +5V rail is in blue. What I wanted to do was see if there was maybe a short or if there was excessive noise going on that went below the threshold. To my surprise, it periodically dipped a lot lower than expected, causing the reset. We definitely have a power supply issue at this point.

    Looking at the power supply circuit for +5V, there isn't a whole lot going on here. How it works, is that an AC line from set of taps directly from the transformer gets rectified and filtered. This makes a unregulated +/- 12V DC. From there, the +12V DC circuit is regulated to 5V using a 2N6057 and MC1723 circuit. 

    Looking at it, my initial guess was the rectifier as these fails often. So I test it in circuit, and suprisingly one of the diodes in it was shorted, specifically on the ones creating the +12VDC line. So if it was failing, it could explain the dip in 5V. What was super interesting was that it didn't pop the fuse. Normally when one of these fails, they take out the fuse. Replacing the rectifier fixed the issue and it hasn't improperly reset since I replaced it with a new one.

    Solution
    Bad power supply bridge rectifier at DB1.
  20. SNESNESCUBE64

    Head On N - Blocky Graphics

    By SNESNESCUBE64,


    Arcade Repair
    I got a pretty interesting board on the bench this time: Head On N, released by Nintendo, Licensed (Or stolen) from Sega. This is an interesting boardset, as this is for the most part a clone of Sega Vic Dual hardware, except they spread it across two boards and included the sound board on the CPU board. I had already done a deal of work deconverting the board, unfortunately this thing was missing a lot of parts and was modded to play an unknown game (the roms weren't included).

    On to the issue. The problem at hand is that there is no detail, just blocks moving around on the screen.

    First thing I did was hook it up to my Fluke 9010A to do RAM and ROM checks. The RAM had been previously desoldered by someone else, so I socketed it (4027 DRAM fail pretty often) and fixed some damage traces done by the previous owner. Everything came back as good, so I figured that the issue was after the RAM, since graphics and system RAM are shared. There are no schematics, but since this is so similar to Sega Head On hardware, I just used schematics for that (I actually used the schematics for Tranquilizer Gun, since Head On used a custom IC for video stuff). Looking at it, the first thing that happens is the graphics data gets serialized. From there, it get's processed with sync and color gets overlayed. Also note that on Head On N, the 74ls166 was sometimes substituted with a 74ls198 (as other Nintendo games like Space Fever used that IC at the time).

    Looking at the 74ls166 (found at 3C) with my oscilloscope. Looking at all the signals, everything except for the output looked correct. Output was stuck high. I decided to hook it up on my logic analyzer just to make sure that it wasn't some weird timing. However, it just seems that the output was always high despite not supposed to be. Notice that it gets loaded, but the output doesn't change despite being enabled.

     
    Pulling the 74ls166 out of circuit to test in my ABI chipmaster, the chip tested bad!

     
    After replacing the 74LS166, the graphics were back to normal. Next step is going to be testing sound!

  21. 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.
  22. SNESNESCUBE64
    This was a fun one. I have a whole box of these boardsets and I figured out which ones had working CPU boards, so I was able to immediately narrow it down to the video board. The initial problem with this board was that the board was doing nothing, just displaying a blue screen.

    Just randomly probing around randomly at the buffers going between the video board and the ribbon cables going to the CPU board. The overall goal was just to make sure that the two boards were talking to each other. I stumbled across H1, a 74ls245. The outputs looked really odd so I decided to just replace it. After replacing it, I was able to see the game! The only problem here was that it was missing ALL moving objects (Notice the guy doing the acrobatics is missing).

    The way hypersports works, is that there are two main sections in which graphics are generated (ignoring the parts that generate clocks and whatnot): Background graphics and moving objects. Down the line they are mixed together to create one full image. With this one, since it was just moving objects, I figured that it was either the data getting lost on the way to the mixing, the ROM/RAM is not getting activated, or there was a selection problem when mixing the graphics. 

    The first thing I did was double check the ROMs were being activated and sending data out. With that verified, I double checked that the Konami 083 custom was outputting data to the color PROM. From there it was checking to see if the color PROM was talking, it was so data was at least making it out. This meant that there should at least have been SOMETHING on screen, so the problem had to be with the mixing together.
    Probing around with the enable and select lines of all the multiplexors and the buffers I noticed that the signals 512 and 5̅1̅2̅ were always stuck low and high respectively. That is super odd as this is clock signal used for selecting these. Tracing it back I ended up at B4, which was a 74ls74, a dual flip flop. Looking at the signals, it was getting acting as it was supposed to, but the problem was that it wasn't getting a valid data input. Moving to the next part of that flip flop, I noticed that it wasn't getting a clock, which is not correct here. I traced it back to B3, which takes the 1H and 4H signals and makes a clock out of them. It is always activated so it should be doing something as long as the inputs are valid. Both 1H and 4H were toggling appropriately (they really should have been if I was getting anything on the screen at all as these are timing for video), but there was no output. This was our culprit. After replacing it, we got our objects back!

    After closely looking at the graphics, this board was all set.

  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
    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!
  25. 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.
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