Centipede cabinet not working

Russtang

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Hello all,

My buddy has a centipede that is not working properly. Here are the symptoms:

White, rolling screen.
1, 2-player buttons lit up.
Random audio pulsing/buzzing.
Won't play blind.

Here's what I tried:
1. Put machine in test mode. No beeps or visible changes on screen.

2. Fuses on power board are all good.

3. Verified all voltages on main board.
5v was reading 4.7v. I adjusted the trim pot until it was 5.0. AC ripple is approximately 750mVAC. Reasonable amount of ripple, or new big blue needed?
36VAC on ARII board is measuring 18VAC with respect to ground. Not sure if I am measuring it correctly by going to ground.
All other voltages check out.

4. Removed edge connectors, used contact cleaner on them and reseated them.

5. Removed/reseated all main board socketed chips.

6. Removed ARII board.
All caps measure in spec out of circuit.
2N3055 power transistor verified good.
Q8 (+12v), Q9 (-5v), Q2 (tip32) check out ok.
Big power resistors check out ok.

Nothing looks burned or blown on the ARII, main board, power board. Any ideas on what to try next?

Thank you,
Russ
 

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measure voltage at the board. I've seen too many different Atari boards the last couple years and can't remember specifically where the test points are but there is a +5 and a ground somewhere. I had a Pole Position 2 board that was completely dead and it wound up being a bad diode shorting the +5 and ground together. I don't know specifically if Centipede is the same way but who knows. :)

another matter entirely is the AR2 itself. they have a feature called Sense which is supposed to automatically adjust +5 higher if in the event it "senses" that it's too low coming back from the board. it's a circuit that feeds +5 and ground to the game board, and then there's wires that go back from the wiring harness to the AR2 for the return. those are the Sense+ and Sense- wires. the fact it was sitting low at 4.7V for you tells me there's something not right.

Sense is great on paper, but in real world use given these boards are pushing 36 years old, they eventually become damaged. I note how in the PSU guide in my signature how to clean an edge connector; don't remember exactly if I explained in detail why you should. but the dirt that forms on the contacts over the years will eventually become like a resistor that blocks power from getting from the power supply to the logic components (or chips) on the board. this will fool Sense into thinking the voltage is too low, as the AR2 gets its reading for what to set this to from the voltage that actually reaches the chips. ultimately what can happen is Sense will exponentially keep increasing the +5 supply to the board until it burns up the edge connector. the pins inside the harness will be damaged from this as well.

I would have to believe since you pulled the harnesses to clean them you would've noticed if the edge was burned up, but there's also another symptom where the pins inside the harness lose their spring tension and don't make adequate contact with the edge connector. I also want to believe that from repeated arcing or that resistor function this could burn an edge connector up too.

just a little bit of outside the box thinking to apply to this. :p I should genuinely add more to my PSU guide for this reason because I keep typing out the whole Sense thing every time!
 
Thanks Mecha for the quick reply.

Yeah, I measured the 5v (and other voltages) at the main board test points.

Thanks for the sense tip. I'll check it out and see what the voltage is reading. Perhaps bypass the LM305 regulator/sense lines altogether and wire in a replacement regulated 5V p/s... Anyone know how much current an average centipede board draws at 5V?

Yeah, the edge connectors were bright and shiny, and the connectors looked clean too. I'll ohm out each connector pin to the edge conn to verify low resistance connections on each pin.

Thanks again for the ideas!
Russ
 
I would imagine the AR2 current is pretty strong. you can get away with a screw terminal power supply on those though. I don't know about any other voltages though, I'm only talking the +5. lol

I would replace the caps on the AR2 though and clean the adjustment pot with contact cleaner.

I'll have to see if I have a picture of the Dig Dug at work. the edge was burned on it. I cut the +5 and ground wires off the harness and put them in a molex plug and ran my own 18 gauge wire to the corners of the chips. since you're channeling voltage into either half of the board this way, it should trick Sense into thinking that the voltage is the same on the return and it should never increase itself.
 
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