(Topic ID: 246426)

Gottlieb System 3 no sound at boot unless manual reset

By brundaged

4 years ago


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#1 4 years ago

I have a Title Fight that boots and plays, but the sound board doesn't generate sound when first powered up.

If I open the backbox and press the reset button on the sound board, it boots up and starts working normally.

Any ideas? I'm not sure if this is the MPU board failing to initialize the board, or something with the sound board itself.

#3 4 years ago
Quoted from ForceFlow:

My first guess would be bad caps that aren't charging up within the time allotted upon a cold boot.

Would this still be an issue when the game has been running a while? Power off-and-on is all it takes to kill the sound board again. It feels like a logic problem; some reset line not getting pulled low or high on startup.

Let's say you're right, though: Which caps would you look at first?

#4 4 years ago

I investigated this a bit more, and the LED on the sound board is locked on when the game first powers on. So it's not running. Hitting the reset button gets it going.

Powering the game off, then on again USUALLY locks up the sound board again. But every now and then it continues to work after the power cycle.

#6 4 years ago
Quoted from ForceFlow:

Maybe something with the board's reset circuit, then? What does the reset button bypass on the schematics?

Gosh, I wish I had schematics.

Something has changed; it only started doing this recently. So it could easily be deteriorating capacitors or oxidizing connectors causing this side-effect.

I'm guessing the reset button simply grounds the reset line on the sound board's CPU. I haven't traced it out, but that's usually how they work. The MPU board is probably supposed to somehow pull the same reset line low on startup, but isn't for some reason.

Assuming all that's true, I guess that leaves one of these:

- Floating ground between the two boards (aren't Gottliebs famous for this?)
- Issues with the connectors between boards
- Voltages too high or low for the reset assert to work (possibly bad caps)
- Logic failure on the MPU board

I don't have schematics so it's hard to get into specifics. I can probably eliminate the first 3 possibilities without schematics. Anyone know where I can find some?

#10 4 years ago
Quoted from Gotpins:

Before you go ripping stuff apart....try going into diagnostics and do a factory restore.

That was a really great idea, but...no luck.

#13 4 years ago
Quoted from slghokie:

pinwiki has a great Gottlieb sys3 with a whole section on sound. Look for section "5.13 Sound Problems"
http://www.pinwiki.com/wiki/index.php?title=Gottlieb_System_3#Sound_Problems

Good idea. I always forget Pinwiki exists...

#14 4 years ago

Thanks guys. You've been a big help.

I can trace the reset line (MR) from the MPU board all the way to pin 1 on the G5 AND gate IC on the sound board. The same reset line drives the other boards too, so since everything else boots it's a safe bet that the sound board is also receiving the reset signal.

We've eliminated the connectors and harnesses as potential problems, and the reset line has to be working on the MPU board. So it's most-likely the IC at G5 on the sound board. I've ordered a replacement and we'll see if that resolves it.

#15 4 years ago

Update:

Not a satisfying conclusion, but I swapped the IC on the sound board with no effect. I have another System 3 game, so I swapped the sound boards and ROMs and everything worked in both.

My guess is the voltages have drifted outside the tolerance of the original board, but the other one has wider tolerances.

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