Armor Attack sound board assistance

MeAndMsP

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Hello. I'm trying to repair / troubleshoot an Armor Attack sound board without the monitor or CCPU or original wire harness(es), and could use some pointers.
I currently have it wired up to a refurbished Condor power supply (on which I've confirmed the expected output voltages at the correct pins).
Happy to provide more detail if someone would like, but at this point I'm basically wondering if this kind of test bench setup is even possible.
(Outerworldarcade has a few videos showing an arduino-based bench test setup, with a custom chip standing in for the data stream from the CCPU, so I think it is possible).

How I have it wired up:
Wall outlet 120VAC 2-wire <--> PS J2 pins 1 & 2

PS J1 pin <--> Sound board J1 pin
. . . . . . . 7 <--> 4 (+25v)
. . . . . . . 8 <--> 6 (-25v)
. . . . . . . 9 <--> 9 (+5v)
. . . . . . 11 <--> 7 (+5v return GND)

Sound board J1 pin
1, 3, 8 <--> 10K pot (1 on middle spade)
. . 2, 5 <--> 8-ohm speaker

Two dumb questions:
1) Does the power supply need ground from the wall? (GND-HOT-NEU instead of just HOT-NEU)
2) Does the +/-25v that goes to the sound board need a way to reference +/-25v return on the power supply? (PS J1 pin 12)


Further testing / symptoms info about the repair for context:
I found the 2N6107 transistor had failed closed, and one of the 22uF 50v capacitors nearby had failed open; replaced both adjacent capacitors and 2N6107.
Both before and after these faulty components were discovered and replaced, I was able to successfully complete the test procedure on 6-10 of the manual.
Also confirmed the various GND and +5v are reaching the correct chip legs as described on page A16-1.

Symptom before the faulty components were replaced was a loud buzzing in the speaker (like an open ground buzzing, I believe, like the buzzing in an amp when you unplug the lead from your guitar).
Symptom after the faulty components were replaced is a looping, sputtering clicking pattern repeating in the speaker ... until the final part of the initial test procedure (load all highs onto IC1-13 ... tap IC3-11 with ground lead), at which point the speaker goes quiet.
Some of the sounds seem like they're "trying" to work when grounding test points in Table 1 on page 6-10, in that each test point now produces distinct, repeatable but weak little gurgles.

Tools I'm using are a multimeter and a component tester. I have access to an oscilloscope at my library, but basically zero experience using one (though I'm willing to learn).

My next step was going to be replacing the 2N6292, 7815 and 7915, even though they seem to be testing fine out of circuit.
Failing that, replace all the electrolytic capacitors on the board, even though none look particularly bloated (it's probably been a good 20 years since any were changed, if at all).

Links for reference:
PS pinout
AA Manual
 
Confirmed that the wiring is correct, to the best of my knowledge given what the manual provides.
I also have ground, hot and neutral coming from the wall into J1 pins 1-3 on the power supply, since I read that's the intended input.

Have replaced the 2N6292, 7815 and 7915, as well as all the electrolytic capacitors (though nothing else replaced tested faulty).

Confirmed that the initial looping, scratching sound goes away when latching even a single "high" into IC3.
Also it seems, to my ear, like it's the same sound as "Lo explosion" - the looping scratching sound can be reproduced by tying IC3-9 to ground.

Checked and re-checked board for shorts, burns, cap leak, dry joints. Tested continuity between IC pins and their destinations according to the schematics.

Tested for GND, +5v and +/-15v on the various IC pins according to page A16-1.

Did every test in the audio section of the manual that doesn't depend on a 'scope.

Discovered that the glass fuse on the power supply is rated at 5 amps rather than 4, so I'll be getting a proper replacement .. but could the fuse 1 amp out of spec really cause these symptoms?

At this point it seems like I have to just start replacing IC chips at random, and/or all the film & disc caps, until at least something changes in the board behaviour and at least provides a clue as to what's going on 🤷

*edit*
Learned some more. I'll add it here since I just posted this last night.

Every single one of my 39K resistors are testing at 11K in circuit.
Maybe that's to do with them being in circuit, but nearly every other resistor on the board, tested in circuit, is pretty close to the expected value.

Exceptions:
R35 5K in circuit vs. 12K expected
R59 26K in circuit vs. 47K expected
R70 23K in circuit vs. 43K expected
R35 5K in circuit vs. 12K expected

Largest discrepancies:
R22 90K in circuit vs. 1.5M expected
R24 7.2K in circuit vs. 390K expected.
Both of those measured as expected out of circuit and the readings were the same when replaced with new resistors.

Again, probably just because they're being measured in circuit, but I'm just taking notes of anomalies as I discover them.
 
Last edited:
It's been a while since I did a top-to-bottom on my AA soundboard, but you are on the right path. You have to be certain about what sounds you are enabling and whether you can hear that sound, even if other sounds are playing over it. On page 6-17 is block diagram 1. If you hear noise for ALL sounds, then it has to be IC26 or something after, and you could use a scope to trace where the signal degrades. If not all, is it the ones that feed into the voltage follower through the CA3080 amps? If it's those sounds, it could be one or more of the CA amps are bad. Since the CA3080 is current controlled, you won't see anything on a scope. And as the outputs are all tied together, a short in one can sink current in the others. I had one go bad and I just replaced them one by one. The manual also suggests cutting each output (pin 6) individually, until remaining normal sounds are restored, you're choice.
 
It's been a while since I did a top-to-bottom on my AA soundboard, but you are on the right path. You have to be certain about what sounds you are enabling and whether you can hear that sound, even if other sounds are playing over it. On page 6-17 is block diagram 1. If you hear noise for ALL sounds, then it has to be IC26 or something after, and you could use a scope to trace where the signal degrades. If not all, is it the ones that feed into the voltage follower through the CA3080 amps? If it's those sounds, it could be one or more of the CA amps are bad. Since the CA3080 is current controlled, you won't see anything on a scope. And as the outputs are all tied together, a short in one can sink current in the others. I had one go bad and I just replaced them one by one. The manual also suggests cutting each output (pin 6) individually, until remaining normal sounds are restored, you're choice.

Thank you for the response and tips. I'd been putting off the step of cutting the pin 6 outputs because it seemed a bit drastic / destructive, so was hoping there might be some other "aha!" insight that might come along ... it's good to know I'm on the right track. The sounds are there, they're just weak and / or garbled / muffled.

Sounds like it's time to A) move on to the troubleshooting step of cutting the pin 6 outputs, and B) sit down with an oscilloscope and learn how to use it -- after all, I'm working on this project in order to learn more about electronics.

Cheers.
 
If all the sounds are there & correct, just low, I'd look @ IC26 & IC24 first. The tank motor, squeak and beep sounds don't go through CA3080s so they can't degrade those sounds.
 
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