Posted By
Dave B
on 2023-02-06
07:01:10
|  Fixing plus/4s
hi, I'm a newbie here, just found the Forum, i have three Plus/4s, two don't display a screen, One, just before it went blank gave a Pixelated blocky multicoulr display. The other wasn't displaying anything. both showed LED lit. I stopped using the original PSU's as they have a tendency to fry the boards due to non switched over voltage, I think I may have fied the boards even though I ordered an aftermarket PSU. I suspect that the TED or PLA and r some Roms may have been damaged. To that end, I have ordered dead test and Diag carts a PLA and a TED chip replacements. However, before I proceed forward, have you any advice?
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Posted By
SukkoPera
on 2023-02-06
08:11:47
| Re: Fixing plus/4s
Well, the "TED or PLA and some Roms" are 90% of the machine, you can rest assured the problem lies in one of those... or in the CPU  .
Jokes aside, since you have a working machine you can swap the chips one by one and figure out which one(s) is (are) bad. Start with the CPU: take it off one of the failed machine, put it in the working one and power it on. If it doesn't work, you have a bad CPU, if it does, go on with the TED and then the PLA.
Failure probabilities in my experience are: CPU 50%, TED 40%, PLA 10%. The ROMs are pretty sturdy, I have never seen a failed one.
Before you do that, you might want to somehow mark the working ICs, so that you can distinguish them when you have to put the working machine back together.
Good luck!
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Posted By
Csabo
on 2023-02-09
18:07:14
| Re: Fixing plus/4s
Hey Dave B,
Just following up on your post out of curiosity. By "Diag carts", did you mean Diag264? (If not, it's definitely worth checking out.) Any luck fixing your machines?
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