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Commodore PC 10-iii/ PC 20-iii boot issues

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Postie0717

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May 20, 2021
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4
Hi all,

I'm new here and I have done some searching, but I cannot find an answer to this. I recently picked-up a Commodore PC 20-iii and i am having some trouble getting it to boot. I plug everything in and turn it on and I can hear the power supply fan and HDD spin up and I get 2 beeps from the HDD and the CAPS LOCK, etc... lights on the Keyboard flash and that's it. The floppy drives don't light up or make any noise and I do not get any output from the composite port.

I have the video output connected to a converter box to switch it to HDMI so I can view it on my monitor, and I appear to get a video signal (the no signal indicator goes away and the screen goes from blue to black), but there is no information, just a black screen. I tried hooking it up through my receiver to view it on my TV, but again no luck.

I checked the voltages on the power supply output and I have +4.68v and +/- 11.7v, so I think its ok, but just in case I picked up a new ATX power supply and tired connecting it to the HDD (i still need to make an adapter to hook it to the board) and again it spins up and I get 2 beeps. I know the beeps are from the HDD since it's the only thing hooked up.

I tried booting with nothing connected and again just a black screen and no beeps or output.

I reseated all of the chips that I could and still nothing.

I checked the battery and its not leaking and had 3.7V. I have an external battery try that I can wired in if needed, but I'd rather not cut the original battery off if I don't need to.

I'm not sure what to try next. I have an RGBi monitor, but it requires 220v and don't have a 220v power source right now. I don't have an ISA video card that I can try at the moment.

Any thoughts?
 
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Before this PC will boot from FDD/HDD at all, it will show several messages on the screen. So the first thing that has to be done is to find out if the PC sends those messages. Is there a possibility to make sure that this converter box works fine by testing it with another computer?
Another thing: my PC20-III only gives some beepish sounds after all these messages but before starting to boot. It certainly are not two beeps.

Where do you live? Not having 220V means not living in Europe which limits me helping you with physical parts.
 
Thanks for the assistance Rud.

I have confirmed that the converter from composite to hdmi does work, i tested it with my Wii, so it looks like my first step will be getting a video signal. Any ideas? I'm still iffy about the power supply. I know it tested ok, but I'm still going to replace it with a new one once the parts come to adapt the new power supply to the old connector.
 
Postie0717 said:
Any ideas?
Click to expand...
To be honest? None. I have several of these machines and so far I only ran into minor problems like bad ROMs or RAMs, broken CPU and empty built-in batteries of the RTC. No video problems so far. And if I cannot reason what the error is, the next thing that I would do is swapping ICs with a good board. The moment that that one stops working, I think I found the culprit. And finding the bad IC probably does me good: I don't have spares except the good ones of other unrepairable boards.
 
Thanks for the info Ruud.

Ok, so I have confirmed that the power supply and the video convertor both work just fine. I picked up another machine, verified that it worked, and used it as a test bed for the power supplies and the video out. I'm beginning to suspect that its a video issue with the original machine. I'm wondering if its a PAL vs NTSC issue? I didn't think it would matter for the composite out, but i might be wrong. Would the RGBi out work better? Also i tested the HDD in the working machine and it still beeps twice and i get a no boot disk found error. Interestingly after the ram test, but before the boot disk error, a 1701 code pops up. Any ideas what this means? Thanks.
 
CGA composite output is always either NTSC or black and white, but never PAL.
Since you didn't mention any battery leakage, I assume that there is none. I have read that interrupted traces to the floppy controller are not uncommon in those machines in the presence of battery leakage.
 
Postie0717 said:
... a 1701 code pops up. Any ideas what this means? Thanks.
Click to expand...
That means that the HDD does not work.

FYI: I use my PC20-III in combination with XT-IDE. It has one 20 GB HDD (only 8 GB available of course) and a CF card slot. I use that one to exchange data with other machines.
 
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