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Author Topic: Centipede PCB issues...Bad ROMS??? No... bad RAMs...  (Read 1454 times)

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ArtMAME

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Centipede PCB issues...Bad ROMS??? No... bad RAMs...
« on: November 09, 2006, 10:15:13 pm »
I have a Centipede PCB that produces this screen shot on the monitor...

It is just kinda stuck there... every now and then I see a segment of a Centipede here and there, but it stays mostly zeros on half of the screen like in the pic.

C55 thru C58 were damaged in shipping, I replaced them, but if I remember correctly, it did the same thing before I replaced the damaged caps.

I have re-seated the ROMS, but no change...

Any suggestions would be apreciated.  :notworthy:

Thanks...
« Last Edit: November 10, 2006, 08:38:39 am by ArtMAME »
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RayB

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Re: Centipede PCB issues...Bad ROMS???
« Reply #1 on: November 09, 2006, 10:17:54 pm »
Put it in self test mode and listen to the beeps.
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ArtMAME

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Re: Centipede PCB issues...Bad ROMS???
« Reply #2 on: November 09, 2006, 10:29:37 pm »
I get 3 beeps...manual says it is possibly RAM in K7 location...

Info on the IC is:

AMD9101CPC
P2101A
8218EMP

Looks like a 22 pin RAM chip... does anybody know if it is TTL, CMOS, etc...?

Will any old 22 pin RAM chip be a suitable replacement for it?
« Last Edit: November 09, 2006, 10:46:44 pm by ArtMAME »
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Re: Centipede PCB issues...Bad ROMS???
« Reply #3 on: November 09, 2006, 10:48:24 pm »
From the manual that I have, 3 beeps is possible bad RAM at K7.

Cheers

EDIT: I see that you looked that up while I was posting .. never mind,
« Last Edit: November 09, 2006, 10:50:25 pm by CheffoJeffo »
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ArtMAME

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Re: Centipede PCB issues...Bad ROMS???
« Reply #4 on: November 10, 2006, 05:54:45 am »
Well, looks like Bob Roberts has some of those AMD9101 RAM ICs.  I will get a few of those and see what happens.

Thanks for the input guys... :cheers:
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Re: Centipede PCB issues...Bad ROMS???
« Reply #5 on: November 10, 2006, 12:44:51 pm »
Well, looks like Bob Roberts has some of those AMD9101 RAM ICs.  I will get a few of those and see what happens.

Thanks for the input guys... :cheers:

Before you do that, check the pins, make sure the chip is securely in and there are no cold solder joints. Also check for a capacitor near this ram and make sure it is ok as well as all traces around there
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Re: Centipede PCB issues...Bad ROMS??? No... bad RAMs...
« Reply #6 on: November 10, 2006, 04:53:08 pm »
I fixed about 3 of those boards. If you replace those rams, spend the extra .50 and put in the chip sockets. 

Looks like Ram errors galore.  Are they rusty?

My advice is get a logic probe and a 5v power supply.  You can find out what input and outputs on those chips are high low or 0.  Then find one that works and check the other ones to that one. 

If one is out, you probably got another one out, and soon they will all be out.
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