| Posted By
Corsair24x2
on 2010-10-12
22:38:58
|  Partially Functional PLUS/4
Allright guys, 15 years ago I bought a Plus/4 at a garage sale for five bucks, and i finally got on ebay and bought a power supply for it. So, I get it all hooked up using my c-128 setup.....
I get the purple-bordered screen with a white background and black text that I have never seen before! Commodore basic 3.5....60671 bytes free...
and three @ across the screen in a diaganol pattern.....everything else appears fine, so I press F1 to access the built in software...and then this:
(black screen, black border, yellow text, three @ still there)
break
pc sr ac xr yr sp
;1d43 32 08 00 00 rr
So, what could be happening? Any poke codes I can use to check the rest?
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Posted By
Corsair24x2
on 2010-10-12
23:18:12
| Re: Partially Functional PLUS/4
Upon disassembly, it looks like Capicitator on the bottom side of IC UT2 is damaged.
I pushed in some of the ICs, thinking after years they might have come loose from their sockets, and when I rebooted, one of the @ artifacts was gone. I attempted to load the built in software, but it failed again and then the @ artifact returned, this time blinking!
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Posted By
siz
on 2010-10-13
02:25:46
| Re: Partially Functional PLUS/4
Looks like a RAM read failure to me.
The diagonal pattern suggests me that when the lower byte of the read address is zero the value read will also be zero. (@ character in black)
Can you tell the exact position of the @ characters (row, column?)
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Posted By
Corsair24x2
on 2010-10-13
14:54:20
| Re: Partially Functional PLUS/4
Well, I can wen I get home - but if its a RAM issue, its probably related to the bad capicitor - im going to source and replace this in a few days.
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Posted By
TLC
on 2010-10-14
11:54:22
| Re: Partially Functional PLUS/4
Your machine doesn't appear to be "very" sick (...if such distinction is applicable for a case like that :-D )... the problem should be related to what you've already found (did you mean U12?... that's indeed a ram chip), or some other damage around there.
And like you suspected, after that many years (AFAIK they stopped producing the machines around 1986) sometimes the ic sockets can also be blamed (the CPU, the TED, the FPLA and the ROMs are socketed) ...although, these sockets are considerably better than those frequently blamed for problems of the early VIC-20s and PETs, so, problems like that are still relatively rare.
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