Help Needed With Dead Commodore PET

[Cudgel737]

Hi

Not sure if anyone else is interested in these but if anyone can help I'd would be incredibly grateful. I have two Commodore Pets that seem to be completely dead when I turn them on. There is power from the transformer to the main board but beyond that I am lost. I have read on other forums talk about measuring voltages on pins but it just leaves me mystified. My testing kit consists of a multimeter. If anybody would be willing to help get these going I would really appreciate it. It would be great if someone could take a look at them but very simple advice would be appreciated. I was thinking of ripping the inards and converting them to Windows pc's but they are so beautiful it would be a crime.

Thanks for reading

Alec

[Zelandeth]

Stripping machines like this out would indeed be a terrible shame, especially if they're in good condition otherwise and complete.

The PET isn't a machine I'm familiar with (I've never seen one in person), but generally the first thing to try with any older computer that's playing up is to remove and reseat any connectors and/or expansion cards. The contacts oxidise over time and cause poor contacts - the results of this depending on what those contacts do can vary between erratic behaviour to completely dead machines.

You also say that you've got power from the power supply to the main board in the machine - have you checked that this is of the correct voltage? It's likely after this long that there are components in the power supply which may need attention.

Hopefully someone who knows their way around these machines better will chime in soon and be able to give you some better advice!

[SteveCG]

I haven't taken the covers off a Pet, however I have taken the covers off quite a few older machines. Tarnished contacts can indeed be an issue with these computers. As well as switches and card edge-connectors, also look out for ICs (the little black plastic packages with many connections coming out of them) that are just plugged into the computer using IC holders. The connections are often a little tarnished. Gently pressing on them can force a new contact and get things going.

Of course the correct way to solve the problem is to remove the ICs from the holders (remembering their orientation wrt the holders) and gently apply some contact cleaner to the IC's pins. However this requires a little experience and perhaps is not for the novice as IC pins are not rugged things.

[g8jzyian]

Hi,

The manuals are here
http://www.zimmers.net/anonftp/pub/c.../ALLFILES.html

regards

Ian

[Lucien Nunes]

Because the PET is a machine with an integral monitor, it is possible that the computer itself is fine but there's no display on the screen due to faulty monitor electronics. Although I have a few different models of PET I'm not an expert on them myself but I know a couple of people who are, so I will give them a heads-up as they might be able to help - please can you confirm which model(s) they are?

Please do not gut these machines, nor take risks with poking around inside. One wrong move with a meter probe could kill an otherwise good vintage computer that just needs a bit of attention to the display circuitry.

Lucien

[Cudgel737]

Thanks to everyone who has replied.
The manuals are interesting but I am afraid I just don't have the skills to utilise them.

Lucien, if you can put me in touch with someone who can help that would be great. Both the pets I have are 3032's.

Thanks again

Alec

[val33vo]

If you have the skills I would put a scope on the crystal to see if the clock is running, If so then scope each address and data line to see if any are dead ( ie shorted to + or the - supply line or as has been suggested previously it may be the VDU ( visual display unit )

Why not just buy or obtain a PC ? much faster and better than vintage technology like this ( To my own sins I still have a Sinclair spectrum ) which is about as much use as a ashtray on a motorbike nowadays

regards

val33vo

[Andy Doz]

There's a 7812 (or maybe 7815?) voltage regulator in the monitor which was a frequent failure, either going open circuit completely (no display) or going short circuit (hum bar).

My memory fails me (no pun intended) as to whether it's a 7812 or 7815 ..

Think of all these I scrapped back in the day, would love one again! My small repair business ran on one of these until the mid 90's!

[arjoll]

Terry Stewart, who runs the Classic Computers website has fixed a few issues with his PETs. He'd be a very good person to have a talk to - he's quite approachable, there are some blog entries on that website about repairs to his PETs and it's worth joining the forums on that website.

[G8VAT Wolfman]

Just another thought... since they are integral monitors.. is the brightness/contrast turned up?
On a computer course last year that was one of the faults we were given to test our mettle.

Not trying to poke fun or anything cos I bet most of us have been caught by that one at some time (Especially those old HMV 1500s where the brightness slider was upside down).

[Cudgel737]

The brightness is definitely turned up.

As for things that require skills - mine don't extend far beyond choosing between a big hammer or a small hammer.

I am really hoping someone can recommend somewhere to get it repaired or put me in touch with someone knowlegable who would take a look at it for a not too extortionate fee.

However thanks for the suggestions made so far and I'll follow up the ones I am capable of.

[G8VAT Wolfman]

I would gladly take a look for you, however, I am a long way hence... I'm sure there must be someone more local.

I had several of these to repair at my shop back in the late eighties, I can't remember anything personal about them but the old technology can't be too difficult..

[Cudgel737]

G8 that is a generous offer and I'll bear it in mind. As you say it is a long way but if I have no luck anywhere closer it might be worth some postage.

Thanks again.

[llama]

Don't forget the Forum Courier Service: "Equipment Transport Requests & Arrangements". For instance, I have a sister in Dorset and another in Yorkshire. I can't offer their help as I don't think they'll meet up any time soon but you can see the sort of possibilities that exist.
Graham

[G8VAT Wolfman]

To be honest I was surprised that no one nearer has offered.. given the high technical expertise available hereabouts.

I might even have some old Commodore components tucked away, but they are more likely from Vic20 or C64.

But if the courier service is available..

[Cudgel737]

I was hoping there would be someone a bit closer who would be willing to have a look but seems I am out of luck. Can someone tell me what the courier service is and how I could use it?

Thanks

[Darren-UK]

It's this forum section as explained in post #14. Have a look and you'll see how it works. In your case you'd post asking if anyone could take your Commodore from Dorchester to Selby, or wherever, and back again.

It's also polite to mention a contribution to fuel costs if anyone who offers to help is going somewhat out of their way to do so.

[skippar]

Originally Posted by Cudgel737

I was hoping there would be someone a bit closer who would be willing to have a look but seems I am out of luck. Can someone tell me what the courier service is and how I could use it?

Thanks

Did you ever have any joy with these computers? I service and repair Commodore computers and peripherals, namely the Amiga flavours.

Cheers,

Paul.

[Cudgel737]

Hi

Not so far. Do you no anything about PETs and where are you based?

Thanks

Alec

[skippar]

Originally Posted by Cudgel737

Hi

Not so far. Do you no anything about PETs and where are you based?

Thanks

Alec

Hi Alec, I know their history and have the competency to repair them providing applicable parts/components can be sourced. I'm up the M5 from you; Bristol.

Cheers,

Paul.