Commodore PET problems. - UK Vintage Radio Repair and Restoration Discussion Forum

MeanDumpsterCat · 5th Mar 2015, 1:00 am

So I have had a recent failure from my Commodore PET 2001 16N.

Started while in normal use when the brightness control was moved.
The computer suddenly froze and displayed
'?ILLIGAL QUANTITY ERROR'

I rebooted it and it just gave me a blank screen
After a while it hung on the garbage character screen
And currently it is booting into BASIC just fine with everything working and then a few seconds later, freezing and crashing completely.

My best guess is that it's just a capacitor (or a few) that are just not tolerating what they are supposed to when they heat up by a small amount but I would like some second opinions and some advice on how to go about diagnosing and fixing. This is a treasured computer of mine so I would really like to fix it.

Many thanks
-Dan

paulsherwin · 5th Mar 2015, 1:40 am

I have no experience of fixing these (though I did use one in 1980) but bad electrolytics are always the first thing to look at with these symptoms.

camallison · 5th Mar 2015, 10:44 am

Power supply caps or internal supply line caps are the main suspect. I worked in the team that introduced these to UK manufacture and remember those caps being marginal spec.

Colin

SteveCG · 5th Mar 2015, 5:07 pm

I've not looked inside one of these. Are any of the ICs mounted in holders - as distinct from being soldered to the motherboard? If there are some then try gently lifting them up a little and then re-seat them.

jay_oldstuff · 5th Mar 2015, 11:32 pm

Pretty much all ic's in a PET are socketed, one thing I would say is the board is full of tantalum capacitors and pound to a penny some of them will be on there last legs by now.

Jay

MeanDumpsterCat · 6th Mar 2015, 12:31 pm

Thanks a lot for all the help, guys. I'll definitely try cap replacement . Does anyone know where I can find details on the electrolytic and tantalum caps that the commodore PET uses? Just to make life a little easier.

5th Mar 2015, 1:00 am	#1
MeanDumpsterCat Pentode Join Date: Oct 2014 Location: Selsey, West Sussex, UK. Posts: 204	Commodore PET problems. So I have had a recent failure from my Commodore PET 2001 16N. Started while in normal use when the brightness control was moved. The computer suddenly froze and displayed '?ILLIGAL QUANTITY ERROR' I rebooted it and it just gave me a blank screen After a while it hung on the garbage character screen And currently it is booting into BASIC just fine with everything working and then a few seconds later, freezing and crashing completely. My best guess is that it's just a capacitor (or a few) that are just not tolerating what they are supposed to when they heat up by a small amount but I would like some second opinions and some advice on how to go about diagnosing and fixing. This is a treasured computer of mine so I would really like to fix it. Many thanks -Dan

5th Mar 2015, 1:40 am	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,959	Re: Commodore PET problems. I have no experience of fixing these (though I did use one in 1980) but bad electrolytics are always the first thing to look at with these symptoms.

5th Mar 2015, 10:44 am	#3
camallison Heptode Join Date: Feb 2013 Location: Yarm, North Yorkshire, UK. Posts: 535	Re: Commodore PET problems. Power supply caps or internal supply line caps are the main suspect. I worked in the team that introduced these to UK manufacture and remember those caps being marginal spec. Colin

5th Mar 2015, 5:07 pm	#4
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Commodore PET problems. I've not looked inside one of these. Are any of the ICs mounted in holders - as distinct from being soldered to the motherboard? If there are some then try gently lifting them up a little and then re-seat them.

5th Mar 2015, 11:32 pm	#5
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Commodore PET problems. Pretty much all ic's in a PET are socketed, one thing I would say is the board is full of tantalum capacitors and pound to a penny some of them will be on there last legs by now. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train

6th Mar 2015, 12:31 pm	#6
MeanDumpsterCat Pentode Join Date: Oct 2014 Location: Selsey, West Sussex, UK. Posts: 204	Re: Commodore PET problems. Thanks a lot for all the help, guys. I'll definitely try cap replacement . Does anyone know where I can find details on the electrolytic and tantalum caps that the commodore PET uses? Just to make life a little easier.