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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 9th Jun 2022, 5:33 pm   #1
pudwink
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Default Just got myself a commodore pet setup but not working

Hi all
I always wanted a Commodore pet computer and after years of looking I have now got one a Commodore 4032 and a 4040 disc drive only problem is neither are working.
The 4032 makes the chime noise when switched on but nothing onthe screen and the 4040 seems to be completly dead.
working a bit backwards I thought I would look at the disc drive first as it could be an easier fix I found a recent post on here for the same drive and as in that one I found no voltage at CR7/8/9 on the main board but unlike the previous post the wiring looks fine although onthe bottom of the transformer there is the earth neutral and live going in but there is a red snipped off wire next to them but is this for 110v?.
The fuse and switch test fine I would like to test for voltages coming out of the power supply but dont know what each one is so any help would be brilliant.
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Old 9th Jun 2022, 5:51 pm   #2
SiriusHardware
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Default Re: Just got myself a commodore pet setup but not working

Forgive me for asking Pud, but did you just acquire those in the last few days? If it came with a printer as well I have to say you got it for an amazing price. If that wasn't you, ignore everything I have just said.

I'd like to suggest that these be tackled in separate threads so maybe if you focus on the computer in this one and start another thread for the 4040 drive.

This PET may be a little bit different to the ones we have seen before so we will need to scrape together the right resources (circuit diagrams, etc).
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Old 9th Jun 2022, 5:53 pm   #3
ScottishColin
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Default Re: Just got myself a commodore pet setup but not working

Watching with interest.

I'll help if/when I can, at least with some comparisons.

Colin.
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Old 9th Jun 2022, 6:06 pm   #4
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Default Re: Just got myself a commodore pet setup but not working

Pudwink, does your PET mainboard look like the attached diagram?
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Old 9th Jun 2022, 6:32 pm   #5
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Default Re: Just got myself a commodore pet setup but not working

... or is it more like this one?

Alan
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Old 9th Jun 2022, 6:58 pm   #6
pudwink
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Default Re: Just got myself a commodore pet setup but not working

Hi
Firstly no I did not get the one with the printer but from the same site.
Alnd here is a picture of my board in the pet.
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Old 9th Jun 2022, 7:24 pm   #7
SiriusHardware
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Default Re: Just got myself a commodore pet setup but not working

OK, looks like AJ has the right of it. Could we ask you to put that image into a .zip file and attach it to a post? The forum downsizes all posted images to a maximum of 800 x 600 so it isn't possible to read much of the detail on the photo in post #6.

Something else you can do is just to take the rear cover off the monitor and - in a dark room - power on and have a look to see if you can see a dim orange glow in the tube neck. It may take a few seconds to get up to full 'brightness'.
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Old 9th Jun 2022, 7:48 pm   #8
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Default Re: Just got myself a commodore pet setup but not working

It looks like this is a PET with the CRT Controller (UB13). There's something odd about the voltage regulators on the heat sink though. It looks like the PET has had some 'work' done to it. I've attached the file where I found the board layout. Source was 'zimmers.net' of course.

Alan
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Old 9th Jun 2022, 7:53 pm   #9
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Default Re: Just got myself a commodore pet setup but not working

That's one reason why I want to get a clearer view of the PCB.

All the info I have I have found so far suggests that these have one less TO3 regulator than the older universal boards (only the one 5V regulator) but on Pud's the arrangement of the regulators is, so far, unique. I haven't been able to find an image of another one with that arrangement yet.
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Old 9th Jun 2022, 8:01 pm   #10
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Default Re: Just got myself a commodore pet setup but not working

Quote:
Originally Posted by SiriusHardware View Post
I haven't been able to find an image of another one with that arrangement yet.
Nor have I and judging by the excess heat sink compound and the epitaxial regulator I suspect we won't

Alan
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Old 9th Jun 2022, 8:01 pm   #11
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Default Re: Just got myself a commodore pet setup but not working

I've cropped closely into the board layout from the document AJ linked to in #8 (attached). I'm not sure this is an exact match for Pud's because while a lot of online images do show the screening can which is next to the sounder in the corner on this layout, Pud's PCB does not have that.
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Old 9th Jun 2022, 8:23 pm   #12
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Default Re: Just got myself a commodore pet setup but not working

This one from the middle of the same document looks more like Pudwink's although his appears to have had the third regulator replaced with a more modern type.
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Old 9th Jun 2022, 8:25 pm   #13
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Default Re: Just got myself a commodore pet setup but not working

Have a look at this link and scroll down to Commodore PET 4032. That's the one and it has three regulators rather than two.

http://dunfield.classiccmp.org/pet/index.htm

Alan
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Old 9th Jun 2022, 8:36 pm   #14
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Default Re: Just got myself a commodore pet setup but not working

I think that about pins it down. It's a 4032 universal dynamic PET with 40 column display and one regulator has been replaced with a non-standard part. We now know which schematic to work from so I'll lift the relevant pages out of the main document. It'll be easier to work from. Give me a few minutes.

Alan
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Old 9th Jun 2022, 8:48 pm   #15
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Default Re: Just got myself a commodore pet setup but not working

Done and I've rotated the pages to make things easier.

Alan
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Old 9th Jun 2022, 8:55 pm   #16
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Default Re: Just got myself a commodore pet setup but not working

.... and here's the parts list.

Alan
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Old 9th Jun 2022, 9:31 pm   #17
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Default Re: Just got myself a commodore pet setup but not working

Neat, thanks for doing that. I think we'd better wait for Pud to tell us whether he has a tube neck glow before proceeding any further.
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Old 9th Jun 2022, 9:37 pm   #18
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Default Re: Just got myself a commodore pet setup but not working

Yes and if it is glowing he'll need to check the PSU voltages in the vicinity of J8 and J10 on the main board. I note that J10 isn't connected in the photo'.

Alan
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Old 9th Jun 2022, 10:05 pm   #19
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Default Re: Just got myself a commodore pet setup but not working

The photo of the one you referred to in the link only appears to show a single loom going from the mainboard to the monitor (From J7). If you look at the diagram for the monitor (not included in your dossier) it shows that power to the monitor is AC, going in on pins 1 and 2 of the connector at the monitor end.

It's not clear from the diagram where the monitor is supposed to pick its AC power up from but again, in the image you pointed to I see a twisted pair of wires going directly from the mains transformer up into the monitor housing so I would think that is the AC power for the monitor.

Pud says there is a startup chime, not sure to what extent that may mean that the system is functional, it depends on whether the generation of that startup tone is one of the initial tasks carried out by the firmware.
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Old 9th Jun 2022, 10:21 pm   #20
SiriusHardware
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Default Re: Just got myself a commodore pet setup but not working

Ah, here we go.

https://scruss.com/blog/2018/02/14/c...startup-chime/

That has to be a software / firmware generated sound so if it's making that noise at startup this could be quite hopeful.
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