| Posted By
C=Owl27
on 2020-10-05
20:49:32
 |  Help Diagnose Bad PLA?
Hello Plus4world.
I was wondering if somebody could help me diagnose what is happing with my Plus4.
i.ibb.co/TqWQWdW/PLAissue.png
(image of problem)
It appears soon after I power on the machine.
The symptoms include a scrambled screen.
Or all of the F keys seeming to be pressed at once.
Or random BREAKs happening.
Also my 3=1 has not ever loaded.
Also when I do load a game from disk,
The startup screen appears but as soon as it moves on to game play,
the screen will get scrambled.
Then my TV will say no signal.
But I can hear some beeps and sounds from the game.
Computer is unresponsive each time.
Sometimes pressing RESET button does not work either.
Has anyone here ever encountered this problem?
I suspect (from what I've read) that it is a bad PLA.
I now have microchips and an eprom.
So I could just burn a new PLA
and swap it out.
Anyways has anyone ever burned a PLA?
Do you have any tips on burning I/Cs?
I would really appreciate any advice you could offer.
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Posted By
Retroshire
on 2020-10-06
03:31:39
| Re: Help Diagnose Bad PLA?
I am not sure this signs out a bad PLA. Most common failures on 264 series: CPU, TED or RAM.
Have you measured voltage already? With a bad PSU there will be damage. Value's above 5,25 VDC are suspicious. Measure with load, on the IC pins (pinout VCC). In C16 also the voltageregulator 7805 is common problem, not in P4.
A good method is IC swapping, but then you must have one proper functioning second Plus4/C16.
Swapping the PLA will show directly if it is the problem.
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