Defender sound intermittent.

blown23t

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Have this defender that has been working fine for several years now. it now developed a sound problem. the sound cuts out completely. then randomly comes back for 1-10 seconds then goes out again. does this the entire game play time. in and out. voltages are good, tried the 6808 40 pin on the sound board, with no change. sound pot ohms out ok, as does the wiring to the board. could the caps on that board cause complete sound failure? im at a loss. anyone have any ideas,or common failures for this problem?
thanks...
 
I would replace the capacitors on the sound card if this were my problem and see if that fixes it.
while I was doing that, I would replace the capacitors on the power supply too and resolder any cold solder joints I found on the header pins too.
while I was doing that, I might as well rebuild the monitor chassis with all new capacitors too as that probably needs it too and will freshen up the colors on the screen and make it look like dynamite.
I bought a bunch of ribbon cables a while ago from bob Roberts before his site closed. I would replace those too but I'm psycho that way whenever I get a new to me, DEFENDER !

good luck
 
the crystal, or green wire harness from the rom board, and each set of headers for said harness on the rom and sound boards.

you can do all the other stuff too, it won't hurt it, but the abundance of various sound board failures were caused by what I listed.

if you hear a steady ticking sound it's the wiring harness or cracked solder on the headers. if not, it might be the crystal acting up.
 
Had a Firepower pinball that did this. The header where the volume pot connects had bad solder joints. I replaced the header and it still did it. The problem was that the plating in the hole was bad so I carefully pried up the plastic on the header and flowed some solder on the top side of the board.
 
Ok, thanks guys. gives me some sense of direction. monitor was a nos 2 years ago. has a beautiful pic. and i already replaced the ribbon cables 3 months ago. i will work on this, this weekend and report back. many thanks guys...Oh,it also has a happ power supply voltages are good.
 
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Have this defender that has been working fine for several years now. it now developed a sound problem. the sound cuts out completely. then randomly comes back for 1-10 seconds then goes out again. does this the entire game play time. in and out. voltages are good, tried the 6808 40 pin on the sound board, with no change. sound pot ohms out ok, as does the wiring to the board. could the caps on that board cause complete sound failure? im at a loss. anyone have any ideas,or common failures for this problem?
thanks...

If the sound is going in and out, the digital portion of the sound board is working....

There's no watchdog on the sound board, so if the code runs off into the weeds, it never comes back.
 
I just went through a stack of 5-6 of these boards that were intermittent or not working at all. About half of them had the bridge rectifier at the input going bad. It would test fine with a meter but when current was drawn the forward voltage would go as high as 12V! (with only 10-20mA being drawn) Try monitoring the voltage test points on the actual sound board while the failure is happening. These are AFTER the bridge.
 
I would also check the potentiometer for the volume control. It is 5k ohms and external to the board. Sometimes just exercising them full rotation a few times can fix (temporarily).
 
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