Quoted from mbaumle:Recently brought home a super clean TX-Sector. Got it set up, played a few games, turned it off, and flipped it back on a little while later to find that I no longer have sound.
I noticed the LED on the sound board doesn’t flash. Game boots and plays just fine, just no sound.
I also checked the 5v on the CPU and it was 7.5 (YIKES). I tried adjusting the voltage with the pot on the board, but it was completely unresponsive. I’m venturing to guess this is keeping the sound board from booting.
Anyway, I bought a replacement voltage regulator board (and an auxiliary voltage regulator board just for completeness).
Game hasn’t been run for an extended period of time with the voltage out of spec like this, but what are the odds I damaged the sound board permanently? Is there anything I should check in the interim?
Edit: ground mods have been done. At least, the mods in the lower cabinet.
Thanks guys!
FIXED!! I wanted to follow up on the repair and diagnostic procedure just in case anyone else runs into a similar problem. Credit goes to a very helpful pinsider, yfz450, who reached out to me and went well beyond the call of duty to help me get this going again. Sound board issues seem difficult to diagnose, so I want to share my procedure in case anyone else finds themselves in a similar situation.
Problem: 5v Power supply was sending too high a voltage through the boards. Soundboard failed to boot. Game had no sound.
First repair: Replaced both the 5v power supply (A2) AND the Aux Power Supply (A5) (which also contains the amplifier circuit). Verified all voltages, all were in spec.
Outcome: Still no sound, however, the heartbeat LED on the soundboard indicated it was booting now.
I swapped the soundboard from TX-Sector into my Robo War. The board worked find in Robo-War, so I know that there wasn't an issue with the sound board. I even flip flopped the ROMs around, so I knew the ROMs were good as well (i.e. kept the TX Sector ROMs in the soundboard while installed in Robo-War.) However, still no sound when installed in TX.
Moving forward: Z13 on the driverboard sends the soundcall signals to the soundboard. I dug out my trusty logic probe and probed the pins. In attract mode, it tested: Pin 1: high, Pin 2: low, Pin 3: High, Pin 4: Low (this pattern continued across all pins). I compared this to my Robo-War: Same logic levels. I swapped out driver boards just to be sure, and It didn't change the situation in TX. Still no sound.
Moving farther upstream: Z27 and Z31 on the MPU board feeds signals to the driver board to generate sound call information. Again, pulled out my logic probe. In attract mode the logic levels were:
Z27
Pin 1: High
2: low
3: high
4: low
5 high
6: low
7: low
8: low
9: blank (no signal, neither high nor low)
10: low
11: high
12: low
13: high
14: high
Z31 (which is a SN7408N)
1-7: all low
8-13: all low
14: high
These tested identically to the chips in my working Robo-War as well. When starting a game, and hitting targets, pins 8-12 can be seen pulsing through the probe--indicating that calls are being generated.
So, what now? I've verified that the soundboard and the ROMs are working. I've verified that the driverboard is working, and I've also verified that the MPU is working. Maybe sage the game to chase out the spirits and electrical gremlins?
CONNECTORS! It has to be the connectors, right?
Nope. Connnectors are clean, tight, and untarnished.
Ground problems?
Nope. All the ground mods are done.
Downtrodden and exhausted, I ended up switching out the new Aux Power board I got into Robo War. LO AND BEHOLD: No sound in Robo War! I finally narrowed it down.
Chalk this up to the hardest lesson I've had in a while: Don't assume a board is good just because it's new. The replacement A5 Aux Power Supply Board was a dud right out of the box. I reinstalled the original Aux Board, and all is right with the world again.
My best guess as to what happened: That $hitty potentiometer took a dump on the 5v power supply and caused the sound board to fail to boot. I replaced both power supplies thinking I'd future proof it. Aux board was a dud, and didn't need to be replaced.
In a way, I'm glad this happened. System 80B repairs aren't documented too much, and I didn't really understand the platform as well as other platforms like WPC or System 11 so this was an excellent exercise in understanding it.