Centipede has no sound

dan10things

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Help, I'm trying to solve an issue with a Centipede where it has no sound. I've swapped in another game board and AR2 and had the same problem, so it's not one of those. I've checked the wiring at the speaker, it's good, and I can hear a hum from the speaker when I boot up the game. What else could it be? The volume pot died? Any help would be appreciated. Thanks!
 
1. Bad POKEY C3
2. Bad LM324 K10
3. Missing +12V or -5V

Are you sure the other game board is good?

Ohm out the POT.
Check the edge connector.
 
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Great advice, but I think I've eliminated the top 3 by trying another working game pcb and AR2 from another working Centipede.

I am noticing a crack in plastic on the bigger connector to the board at the top... that might be the problem. How would I ohm out the volume pot? I'm a newb on that. Thanks!
 
How does trying another pcb rule out 1 and 2?

Hope that your issue is 2 and replace the amp, if not it's probably 1.
 
Check the volume pot. Make sure the wires are still connected and that the pot is functioning properly.
 
  • Ohm out the speaker and make sure it's 4ohm or 8ohm (and not open).
  • Ohm out the VOL POT to make sure it is correct impedance (and not open).
  • Follow schematic and make sure VOL POT is connected correctly with respect to all wiring connections / connectors etc.
 
Ohm-out = check the resistance of.

To check the resistance of your pot:
Set your multimeter to resistance (the horseshoe looking symbol).
The pot will have 3 terminals.
Ignore the middle terminal for this test.
Put your meter leads on the outer terminals and tell us the reading you get.

To check the resistance of your speaker:
Remove 1 speaker wire (it doesn't matter which one).
Put your meter leads on the speaker's terminals.
Tell us the reading you get. It should be very close to 4ohms or 8ohms.
 
Thanks for you continued advice folks.

Speaker reads 7.5 ohms
Volume pot reads 49 ohms with the black lead closest to me, when reversed 42.8
Fuses all test fine.
 
Check for 10.5 volts between pins 1 and 4 J5 on the power brick. If it's missing check fuse F3 & bridge CR1.

If that's good make sure you have 10.5 volts at pin 5 of the amplifier IC's Q1 and Q5. The signal comes in on pin 1 of those IC's and the amplified output is pin 4.

J8 pins 3 and 4 on the AR board go to the volume control and speaker. The volume control is actually an L-Pad so to test the speaker you'll need to disconnect one of the wires otherwise you'll be reading through the L-Pad.
 
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