Re: Diagnosing a dead Asteroids board - questions

Phil Morris wrote:
>
> Replaced the CPU (the original was dead as a dodo)
> Added a crystal (the original had been cut off once upon a time)
> Replaced a badly overheating 74LS259N at location M11
> Discovered a burned track from edge connector pad 'D' to the Collector of
> the 2N6044 at Q12 (although continuity is fine, as is resistance on this
> track - it's for COIN CTR-L)
> Replaced ALL the EPROMs/ROMs (some of the originals were bad, so I thought
> I'd do a new set)
> Replaced the 74LS245 at E3 and one of the 74LS244's next to the CPU (I'll
> do the other 244 soon maybe)
>
> The watchdog is resetting like there's no tomorrow
> I've tried the suggestion to remove and socket the 74LS42 at L6 and lift up
> pin 1 to ascertain whether the VSM or the MPU is likely to be the cause of
> the problem. This didn't resolve the issue so the problem seems likely to
> be on the MPU side of things. The only thing remaining to try here is to
> replace the RAM chips one by one, but surely if one or all the RAMs were
> dead the machine wouldn't be in the state it's in now? I mean, shoudn't I
> at least get a beep or two when putting the machine into test mode?

Yup, that's a dead one all right. Did you replace the CPU with a
6502A? A regular 6502 won't cut it here.

I hope you don't have something like an Atari pinball I fixed one time.
The processor hung and managed to turn on ALL the solenoids. As the
solenoids fried the driver transistors all shorted until the current got
high enough to blow the emitters out of them. Once that was done the
solenoid power went backwards through layers of IC until it got to the
processor buss. Took me 22 ICs to fix that.

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Received on Wed Feb 6 01:07:34 2002