Williams Solved Laser Ball (Williams, 1979) no sound

[tunes3540]

We had some close lightning last week, and the power got knocked out. My directv box was damaged, as well as one of my TV's. My Laser Ball machine has no sound now.
This is a system 6 type 1 sound board.
Pressing the diagnostic button on the sound board produces one sound continuously.
Applying a ground to each of the inputs from the driver board does not produce any sounds.
So, I can assume the problem is in the sound board. The amplifier and volume pots all work, as the diagnostic makes sound.
I'm not sure what the diagnostic is supposed to do on this machine.
I'm not sure where to go from here.
Any help would be appreciated.

Here is a photo of the board.

 

[pinballdaveh]

The sound board makes its own 5 volts. Test the output of the regulator for the correct voltage. A voltage spike could have taken out anything from a chip , other parts, or a trace. Sending the board out to be tested and or repaired is a possibility. Or buying a newer version of the sound board might be better. You have to weigh out the differences in cost.

 

[tunes3540]

5v is all good. I put the board on a bench, and setup a computer power supply for +12, -12, ground. I jumpered the external volume pot connector, and connected a speaker. I have the same results as in the pinball machine.

Test produces one continuous sound. So, I know my bench setup is good.

I went ahead and bought a PIA chip and installed it (I added a socket for it as well). That is a lot of pins, but I did it cleanly.
Unfortunately it didn't fix it. Grounding the driver input pins does not produce any sounds. Test is still looping one sound.

I would think if the microprocessor was bad, it wouldn't make any sounds in test. I would also think the same, if the Prom was bad.

I've attached the schematic as well.
I was maybe thinking of changing IC5 the quad nand gate, but then I realize the test switch does work, which uses 2 of the 4 nand gates. I wouldn't think the other two would be bad, but maybe, I guess.
I guess I'll just have to start changing parts. The traces all look good. There is no physical evidence of any problems.

Clicking the schematic will take you to a larger copy of it.

<a href="https://claytonfelt.smugmug.com/Around-the-House/Pinball-Machine/i-C4mvB37/A"><img src="https://photos.smugmug.com/Around-the-House/Pinball-Machine/i-C4mvB37/0/L/20160829_190524-L.jpg" alt=""></a>

 

[pinballdaveh]

Does moving the red toggle switch do anything? I thought it might be for different sounds. Changing the pia was a good guess. Your logic about the microprocessor chip sounds correct. My guess would be changing the sound prom next, easy swap because it has a socket already.

 

[tunes3540]

Moving the red toggle changes nothing. I've read it might be to change from sound effects to music sounds.
If I change the sound prom doesn't it have to be for this particular game? That would make it harder to find. Where would be a good place to find one?

 

[pinballdaveh]

Marco is usually a good place for proms. And [thatpinballplace] shows to have them. If anybody else knows of a good supplier, please chime in.

 

[Coil_Smoke]

This is a bit of a wild guess about that sound diagnostic circuit. It sure looks like a multi-vibrator . Does throwing the switch just inject the multi-vibrator's Oscillation into the audio stream? It would explain the single tone you are hearing and I bet that tone is a square wave. Does it sound harsh .......?

 

[tunes3540]

Thanks guys for the help. I've ordered a sound rom. That should be easy to try, like you said.

 

[tunes3540]

Latest update, still not fixed.
I installed the sound rom, and it acted differently and not right. I realized it was a rom, and the one removed was a prom. I had to change the 4ea jumpers accordingly. After moving them, which is more soldering, it was back to exactly like the problem started. Test works, but nothing by grounding the pins from the driver board input.
I have checked voltages and determined the inverter chips iC8 and IC9 seems to be working. Grounding those input pins causes the output of each inverter to change.
I am left with the 8 input Nand gate IC4 the 4068 chip. I removed it and have ordered some from ebay. They are cheap.
Keeping my fingers crossed. Running out of ideas.

 

[tunes3540]

Latest update. Fixed!
I replaced IC4 the quad nand gate, but still no change.
I then rechecked IC8 and IC9 the quad buffers. I found that two of the buffers outputs were not high. I replaced IC8 and it started working. Grounding the inputs from the driver board (sound select inputs) on the right side of schematic, causes sounds.

I recently found a web page that explains how this works. The quad input nand gate IC4 triggers an interrupt whenever any of the sound select inputs goes low. Since two of them were already low, the nand gate never changed state.

I now know that if your board tests ok, but no input selection works, either IC4 or IC8 or IC9 are the area to troubleshoot. It could also be the PIA, but not likely. If test works, then you know the CPU and Rom are working.

By the way, that new Rom I put in, does not have the same sounds as the one I removed. I kind of like them, but definitely different sounds. It says laserball on the sticker, but I wonder what game it really is.