Hey guys, I'm hoping I can run into hopefully more helpful or knowledgeable people here, as I posted on arcade-museum and don't really get much help. I know this sound board is shared across many different machines, but this happens to be used in a Defender arcade. This board is the type 2 square one, without a speech card.

I have done so much to try to fix the problem that I am really not ready to admit defeat =\

Issue:
No sound 19/20 times board is powered on. That 1/20 I get sound, it works for maybe 30 seconds and stops.
Pressing the test button on the board has the same results. 1/20 times it cycles the boot sound.

Tools on hand:
DMM, Eprom Burner, Logic Analyzer, Workbench Power Supply

I have been following 3 different repair guides.
- Found this snippet on black knight audio, https://pinside.com/pinball/forum/topic/black-knight-sound-issues-question-about-low-leaking-cap#post-2030638
- Leon's Diagnostic Page, http://home.scarlet.be/~fb054529/soundwill/esoundwill.htm
- Video Recap Sound & Speech Servicing Guide

Fix attempts:
- Replaced all electrolytic capacitors. (Voltages are good at caps)
- Reflowed connector pins.
- Moved to workbench power supply for deeper testing.
- Tested TDA2002 amp, and its working.
- Pulled and cleaned fuse clips and fuses.
- Burned new sound rom into eprom.
- Burned Leon's test rom, ran diagnostics, all tests pass.
- Replaced 6808 with 6802 from another machine, same results.
- Socketed and replaced IC10 PIA 6821 (Just because)
- Socketed and replaced IC4 7408 (Chip had black tar corrosion on pins)
- Desoldered Q1, Q2 and Q3 transistors and tested.

So that this point, i've replaced half the board. Tested most of the other half. Some things that confuse me is I can run Leon's test rom in here, and it passes every test in his diagnostic list, including the ram test of IC11. I've never used the test rom before, so I'm not sure if the sound I get out of the speaker while this test is running is normal or what. While all the chips are pulsing, I get little pops on the speaker about 4-5 a second. I assumed this was normal.. All the IC's are pulsing normally during the test.

When I put in the defender rom and press the diagnostic switch, i usually get a very faint high pitch hum/sound.

Following the Recap guide, I can get through the "new board" section up to a point. I found some errors with it however, so I dont know how accurate it is? For instance, it says to check high @ MPU Pin 36 for reset. Schematics show reset at pin 40. I assume this is an error in the document.

Next section is says Check for Pulsing @ MPU Pin 5 (VMA). I think this might be where my first issue is, as it says it should be high with no sound select inputs, but pulsing low with an input (ie: switch being pressed). I get a high signal here when the board is stuck in its fail state, even after diagnostic switch is pressed. I'm not sure what this means, but I swapped out CPU with known working 6802 CPU at this point, and it still failed. So i continued through the test. I got through IC2, IC4 tests, which showed inputs and outputs pulsing at this point. Then onto IC10, where I now have pin2 input stuck high, and the rest of the inputs low. All outputs low as well. Based on this info is the reason for replacing 6821 PIA IC10 chip. Again, same results....

So now i'm stuck. I supposed I could replace the rest of the IC's, but man. Any insights as to diagnose this further??

MarAlb, thanks for the response. I "think" the DAC is working, because the data it is getting is not pulsing. I got one pin stuck high, the rest low when it gets there, which is coming out of the PIA chip like that. I do get a quiet tone coming out of the speaker, which I think its its interpretation of that high pin into sound?

holy shitballs. Thanks Barakandl, i cut W14 trace and installed a 6802. It's working perfectly now. Odd that the defective ram passed Leon's test rom...