Posted By
DistantStar001
on 2024-07-29
21:29:18
|  Plus 4 not loading/talking to disk drives
Just as the title says. I have a Plus 4 that hangs on disk commands (DLOAD, PRINT DS$, LOAD"$",8 and so forth). Essentially, for load commands it says "SEARCHING FOR..." but just hangs there whether the drive is connected or not. RUNSTOP does not interrupt this. Also, when connected to my Pi5141, the buttons on the drive won't work either.
The symptoms are present when connected to both the aforementioned Pi5141 and a 1541 floppy drive. Both the Pi and 1541 have been tested with multiple C64s, C128s, VIC-20s and my C16. In each case, the drives behave normally.
I tried replacing the TED and PLA since I had working replacements to test, but despite both being tested good in the C16 the symptoms still present in the Plus 4.
Any ideas?
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Posted By
gerliczer
on 2024-07-29
23:56:12
| Re: Plus 4 not loading/talking to disk drives
The result is not surprising as those two have nothing to do with disk I/O. Search for the Service Manual. Even this site has it. Perform the checks written in there and try repairs as the measurements suggest.
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Posted By
DistantStar001
on 2024-07-30
02:06:39
| Re: Plus 4 not loading/talking to disk drives
Downloaded. But it's not as helpful as I hoped
Also, checking BASIC, with a simple "HELLO WORLD!!! " loop and as a two line program, nothing prints on screen. As a 1 line program (10?"HELLO WORLD!!! ";:GOTO 10) works as expected, but RUNSTOP shows a break in line 165. Listing the program also returns: 165 PRINT"HELLO WORLD!!!! ";:GOTO10
Also the power LED cuts out but the computer stays on.
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Posted By
DistantStar001
on 2024-07-30
04:23:05
| Re: Plus 4 not loading/talking to disk drives
It's the 8501. I just swapped it into my c16 and symptoms followed it. Any ideas on a replacement? I've tried using a 6510 with no luck, and the MonoTech 6502 replacements are no cheaper than an actual 8501 from eBay once you factor in shipping.
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Posted By
SukkoPera
on 2024-07-30
05:14:19
| Re: Plus 4 not loading/talking to disk drives
Yeah, I was going to suggest that. You can build the Monotech yourself for much cheaper, or you can get this relatively new replacement by Daniel Mantione which I'm testing to my happiness. If you build it yourself it's supercheap again.
The power led issue is odd, it is directly connected to+5V line. It might suggest a faulty power switch.
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Posted By
siz
on 2024-08-02
02:52:42
| Re: Plus 4 not loading/talking to disk drives
The power LED issue can be a faulty ribbon cable between the mainboard and the keyboard.
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Posted By
Jácint75
on 2024-08-02
04:08:58
| Re: Plus 4 not loading/talking to disk drives
If you have changed the processor and the error persists, then it is not a processor error. The processor port output is amplified by a 7406 (U7) ic. The operation of this IC must be checked!
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