(Topic ID: 220429)

South Park sound vanished

By jjanyday

1 year ago

Topic Stats

  • 4 posts
  • 3 Pinsiders participating
  • Latest reply 1 year ago by Schwaggs
  • No one calls this topic a favorite


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#1 1 year ago

hello out there! been looking thru topics to find help repairing SP.. after years of faithful service, the sound has disappeared..

back story: the cabinet speaker & grill were destroyed by a child long ago, finally got around to replacing them about a month ago, probably not related?
the game has been functioning great until a few days back, the sound got really loud, then quiet, then reaaaallly loud, then gone

what i did: after checking the basics, i swapped in the cpu / sound from monopoly, changing the eeproms U7, U17, U21, U36, U37, U210
problem solved

however: my intention was to work on the cpu on monopoly at home, since SP is about an hour away. problem being the rev d board apparently isn't
compatible with monopoly (anyone refute?). so i drove back there today, swapped the eeprom's back into the original board, and swapped one by one
all the socketed ic's U4, U6, U9, U209, U212... none of which seemed to be the issue..

so i know it's a board problem, i know it's not the eeproms or other ic's i swapped.. machine voltages must be fine..

i'll be heading back there wed / thurs to have another look, & would like to be armed with as much info as possible

thanks for any help

#2 1 year ago

ok little update...

not sure which but apparently i had one of the eeproms not seated properly. tonight i installed the faulty board into monopoly again and the game came to life.

still no sound though.

since the game is now alive, i checked and there is a nice *pop* when the machine is turned on or off.. also i measured voltages on the regulators of + & - 5.65v.. nothing at all when doing the speaker test..

so i gather the speakers, wiring, voltage & amplifier circuits are good, but something is keeping the sounds from getting to the amps.

#3 1 year ago

So to clarify, what's the part number of your cpu board? It's the old style with the socketed BSMT sound chip, not the large surface mount one, correct?

#4 1 year ago

There are 5 voltages used for the sound circuits. +5 -5 +12 -12 (these 4 are considered Analog power supplies) and a +5V digital supply. The analog supplies are used for the op amps and power amps.

Check all 4 of the analog supplies on your board. The 12v supplies are generated on the I/O board so not likely your problem (since you connected the board to 2 different I/O boards). The 5V analog supplies are regulated on the CPU/sound board itself by VR1 and VR2. Check the voltage on pin 3 of each of these or on the + lead of C59 and the - lead of C40.

If the supplies are good, I would start a game (so the board should be playing sounds) and use a logic probe to test pins 6 and 8 of U26 to see if you see a pulsing signal there (the output of the DAC).

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