Defender Sound Board Problem

troxel

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Donor 7 years: 2015-2021
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I usually get the startup sound, intro sound, and then coin-up sound and then no more sounds when it goes to the game. Sometimes I don't even get the 3 sounds at the start.

If I hit the test button, the test sound plays.

I have done quite a bit to this board, and really curious as to what's wrong with it.

Here's the list:
New headers and caps
Replaced CPU, PIA, ROM, EPROM (also verified), TDA2002
Board is jumpered correctly using Rom1
+5 is at 4.83V and the +12 and -12 are present

It's definite sound board problem, because I can put in another one and it works fine.

Any suggestions?
 
Any sounds when you hit the diagnostic switch? My first though is PIA or ram. Tda2002 doesnt go out often, especially if it has been replaced. +5 is a bit low but I think the sound uses the 12v for its operation. Did you replace all of those parts before the sound problem, or after? The reason I ask is because it is very easy to lift traces on the sound boards.
 
Diagnostic switch works with repeated sound. Had the same problem at the start and stayed the same after I worked on it. Replaced PIA and ROM with known working ones.
 
Im a bit rusty on these, but if I remember correctly, the diagnostic does not utilize all of the board, but is more a quick and dirty direct access test. I would have to see theory of operation to verify, but my guess is the buffer ic chips, which could be toasted if it was hit with high voltage at some point. The sound test i think directly accesses the rom, and does not actually test these. Again, I may be totally off, but I will pull some schematics out tomorrow and freshen up on these boards again.
 
got to raise that +4.8 to 5 and see if problem persists
measure it on the sound board and it might be even lower ??

cant remember offhand if the sound card has a ribbon cable, if it does, replace with new
 
I usually get the startup sound, intro sound, and then coin-up sound and then no more sounds when it goes to the game. Sometimes I don't even get the 3 sounds at the start.

If I hit the test button, the test sound plays.

I have done quite a bit to this board, and really curious as to what's wrong with it.

Here's the list:
New headers and caps
Replaced CPU, PIA, ROM, EPROM (also verified), TDA2002
Board is jumpered correctly using Rom1
+5 is at 4.83V and the +12 and -12 are present

It's definite sound board problem, because I can put in another one and it works fine.

Any suggestions?

I'm guessing you pulled voltages from the test points. try replacing the power header and plug. if your voltage is low there, it will be low everywhere else -- depending if you caved in and went switcher or stuck with linear will determine if that's simple or complicated to resolve. the factory headers are awful and you could probably see a minor uptick in voltage by also replacing the plugs. the filter caps on MPU and rom board will all need to be replaced as well. (100 uf / 25V)

there is no ribbon cable for the sound board, but there is a wiring harness that runs from the rom board to the sound board. I would encourage replacing headers and plugs there as well. I had a Joust drop out sounds, wound up being the header on either board, can't remember. I was able to get away with reflowing in that one rare instance. this after I redid the plugs on both ends. I was mad.
 
I'm guessing you pulled voltages from the test points. try replacing the power header and plug. if your voltage is low there, it will be low everywhere else -- depending if you caved in and went switcher or stuck with linear will determine if that's simple or complicated to resolve. the factory headers are awful and you could probably see a minor uptick in voltage by also replacing the plugs. the filter caps on MPU and rom board will all need to be replaced as well. (100 uf / 25V)

there is no ribbon cable for the sound board, but there is a wiring harness that runs from the rom board to the sound board. I would encourage replacing headers and plugs there as well. I had a Joust drop out sounds, wound up being the header on either board, can't remember. I was able to get away with reflowing in that one rare instance. this after I redid the plugs on both ends. I was mad.

Header and caps have been replaced. I didn't replace the plug, but showed +4.99 on my other working sound board. I ordered another 7805 since I didn't have any. Anything else that can bring the voltage down? I also have a linear supply that has been rebuilt along with all other boards.
 
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it won't be the voltage. those things can run abnormally low. I would start at the harness between rom board and sound board.
 
OP has already worked out it's a fault on the sound board itself and not with the harness between boards. Need to check the inputs to, and outputs from IC5

Also worth checking output from IC6 (pin 13) when an input is selected
 
Also worth checking output from IC6 (pin 13) when an input is selected

I've had exactly that problem. The 4068 goes flaky and some sounds start to be missing. If it's an early soundboard it's IC4 pin 13.

Put a logic probe on that pin and and ground each of the sound input header pins in turn, if it doesn't pulse on each grounding that's a problem.

If that checks out ok, next check out the 4050 buffer, IC5 (or IC9 earlier board ), put a probe on each output and again ground each sound input, the output of the 4050 should go low with the input being grounded.

I'd really be leaning towards the 4068 being a problem.
 
Thanks for the input, guys! Hope to have some time tomorrow to look at those 2 chips. Will report back on what I find.
 
Also worth checking output from IC6 (pin 13) when an input is selected

I'd really be leaning towards the 4068 being a problem.

Looks like you guys were correct. Tested with a probe and would work for about the 1st 5 seconds and then would lose the output. Pulled and tested bad in my tester. Pulled one from another board and sounds are back.

Thank you!
 
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