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Display problems on a Commodore Pet 8032

Thats guys for taking the time to reply. I'll have a look today and see if the chips are interchangable. Can I do any damage if the chips aren't identical?

Definatly worth saving isn't it :)
If I get a chance soon I could take some pics of the other vintage computers we have here.
 
Just thinking if you do have some replacement chip/s I could try I wonder if with the magic of paypal you would consider posting and I could try some?
I've looked on ebay and the net but I don't think I'll be getting spares for this one very easily! I'm guessing you all may not be in the UK due to the reply time lag?

Would this be a good purchase to try chips out of or is it a totally different system?

http://cgi.ebay.co.uk/PET-COMMODORE...ptZUK_VintageComputing_RL?hash=item2c538c8ece
 
I still have a bag of various PET motherboards, of which some definitely are 8000 series. Most of them have been marked as broken but may have salvagable chips. I can have a closer look in the weekend to come, and will await any other expert advice which chips or items to suspect. If we come up with something useful, you'll have it for postage + PP fees.

The PET on eBay is a 3000 series one with 40 column display and older Basic. While I think the character ROM is the same, for most part other chips won't be.
 
Thanks Anders, This Pet really have sentimental value too so I really would love it to be right again. :)

I'll pop that character rom out today, if I switch it on without it present and the lines dissapear would this help or would the whole pet just sit in a dead state?
 
mrmacca said:
I'll pop that character rom out today, if I switch it on without it present and the lines dissapear would this help or would the whole pet just sit in a dead state?
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I was just wondering about that whilst reading through the other replies. It's not an exhaustive test, but if the lines are there with no ROM at all, you can be pretty sure the ROM isn't the problem. If there are no lines, it's likely the ROM is bad, but not 100% certain.

I would recommend properly diagnosing the fault before sourcing replacement parts. Swapping parts out isn't a bad approach if you happen to have an identical working machine to borrow bits from, but when each part needs to be ordered/shipped individually it can become pretty frustrating. If you're lucky it's only the character ROM that's bad, but these problems often have a recursive nature - just when you think you've fixed it, another problem suddenly becomes apparent. Replacing soldered-in chips isn't something most people do just for the fun of it, either ;-)

PS. Most of us have our locations in our profiles, which can be seen at the top-right of each post. Some of your replies couldn't have come from much further away from the UK! ;-)
 
More fiddling this morning.

I removed and reseated all the mid sized chips to no avail.

I'm leaving out UD11 as it seems to be irrelevant,

Take out UA3 and the whole screen fills totally green. Put it back in same two lines per character.

Take out UD 10 - Lines remain but loose basic
Take out UD 9, 8 or 7 and you get nothing at all from the machine.

I'm still thinking UA3 ROM is the culprit, dunno why :(
 
Thanks Steve,

I see now, your from the Netherlands. Cool Place. Do you code on Homebrew? (I think its a great peice of code) :)
 
mrmacca said:
Thats guys for taking the time to reply. I'll have a look today and see if the chips are interchangable. Can I do any damage if the chips aren't identical?
Click to expand...
You could potentially do damage to the chip, the rest of the computer, or both. Best to be sure the chips are compatible to be on the safe side. You can use either 2316 or 2332 ROMS/EPROMS. The ones on the ROM switcher may be completely different types. Any of the ROMs on the board should work though; removing them may result in the computer not booting, but that shouldn't matter for this test.
 
Well back with the camera. I've had all of the socketable chips out and back in (as described 3 posts before) I do keep coming back to this character rom :(

I've looked through some drawers and found lots of old chips of the era but nothing exact I could use. Lots of Intel chips circa 1974-79!

DSCF0155.jpg


DSCF0154.jpg


DSCF0153.jpg


DSCF0152.jpg



So now with officially no spares to try I am a bit stuck, heres a better pic of my woes

DSCF0157.jpg
 
mrmacca said:
Take out UA3 and the whole screen fills totally green. Put it back in same two lines per character.
I'm still thinking UA3 ROM is the culprit, dunno why :(
Click to expand...

I agree, the 'cosam' test indicates the character generator ROM is the leading candidate. To prove it, can you borrow a can of "circuit cooler" spray from your electronics engineering department? Spray a little on UA3 and if all clears up, you know it is a temperature problem with UA3. Here is a link to information on this spray: http://mgchemicals.com/products/403a.html

If this is the problem, some of us here will have a replacement ROM or can program a 2532 EPROM chip to replace it. We must keep the PETs alive!
-Dave
 
I suppose I'll be able to mail a character ROM for about £2 including fees. Question is if anyone can do it quicker and cheaper, e.g. within the UK.
 
Like wise if any of the chips I have will help I'll post them on :) Not sure you can make the numbers out in the pics.

There can't be that many PETS still alive can there?

I'm not too sure how to reprogram an eprom. If anyone will willing to post me a ROM I could PayPal them and post return it if it doesn't help me.
 
dave_m said:
I agree, the 'cosam' test indicates the character generator ROM is the leading candidate.
<snip>
-Dave
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I don't follow the logic; can't hurt to replace it I suppose, but why do you suspect the CG ROM (other than that it's socketed and easy to replace ;-) ?) I don't see what removing it proves or even how it could be the CG ROM anyway, especially since the bars are darker than the text.

But if any of those chips in the drawers happen to be 2532s (especially the purple ones with the round labels) and they're not blank, then I'd think that replacing the CG with one of those would prove something one way or another.
 
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MikeS said:
I don't follow the logic; can't hurt to replace it I suppose, but why do you suspect the CG ROM (other than that it's socketed and easy to replace ;-) ?)
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Mike,
Well, I'll admit the socketed part has something to do with it :) , but since the vertical lines are within the character boundries, it can not be the screen RAMs. It might be the serial shift register with stuck bits. What do you think?
-Dave
 
Of course we could treat it like any modern peice of technology and swap the whole motherboard for a working one :D

I've got PayPal remember people if you've got such a board :mrgreen:

I know, I can here you all thinking wheres the fun in that. But for a newbie like me even that would be interesting :listen:
 
dave_m said:
Mike,
Well, I'll admit the socketed part has something to do with it :) , but since the vertical lines are within the character boundries, it can not be the screen RAMs. It might be the serial shift register with stuck bits. What do you think?
-Dave
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I think I'm out to lunch; the apparent difference in brightness misled me, but you're right: it's almost definitely the CG ROM or, less likely, the shift register. I can duplicate the problem by lifting a couple of pins on the CG.
 
Great idea to look for a spare 2532. As long as it is not entirely blank, something will show on screen. It may be complete garbage, but it would be static garbage without the lines. If so, we can be quite certain this chip needs a proper replacement. If the lines appear anyway, you have a different fault that needs diagnosing before solving it.
 
My collegue did look through all these chips and draw a blank. H'es got a good 15 years more experiance then me.

I can't rummage through them now as everything is at work.
 
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