Commodore CBM 3032 'PET' - UK Vintage Radio Repair and Restoration Discussion Forum

stubbyeddy · 28th Apr 2015, 1:45 pm

just got hold of one of these which was dead apart from the screen, after changing all the caps it now shows some signs of life, I get the first full screen image of jumbled characters then a blank one before hanging on a screen with what looks like aliened exclamation marks at regular intervals vertically but only on the bottom half of the display, im sure its bad ROM and or RAM chips and have put on order the petvet from bitfixer but im am a bit out if my depth with this one, if anyone can give me any help or advice please get in touch, id love to get it working again and learn some very basic programming !!

can provide photos if it helps

Eddy

AC/HL · 28th Apr 2015, 8:01 pm

Have you searched online, a quick search turned this up, which may be completely unrelated of course: http://www.verrua.org/pet_repair/

stubbyeddy · 28th Apr 2015, 9:30 pm

thanks for that link, after reading that from what I can make out it has to be bad roms I can get hold of the roms online and the 2532 EPROMS but i dont have a eprom programmer ! can anyone help me out?

cmjones01 · 28th Apr 2015, 10:01 pm

I've never worked on a PET, but on lots of other vintage microprocessor systems, and a fault like you describe would usually be a RAM fault. A quick Google suggests that the video RAMs may be 2114s, which are very often faulty in equipment of this age. The program RAMs are probably 4116 DRAMs which can also give trouble. Faulty ones often get hot, which is a good clue. The static RAMs (2114s) can often be diagnosed by 'piggybacking': just putting another (known good) RAM chip on top of the suspect one. If the fault is fixed, or changes, you know you've found something.

The machine is clearly doing something - if it's clearing the screen, the CPU is running, so you can't be far off!

Chris

acollins22 · 3rd May 2015, 11:14 am

I had a fault on my 4032 which prevented it coming up. The screen would clear and I heard a beep but nothing else. This was down to a faulty PIA chip on the IEEE interface. I pulled the chip and it booted fine.

If you have a scope, take a look at the clocks and the _INT_ line. The faulty PIA was holding it down on mine.

Circuit diagrams are out there and there is plenty of info.

Good luck and keep us posted.
Andy.

28th Apr 2015, 1:45 pm	#1
stubbyeddy Pentode Join Date: May 2005 Location: Newtown, Mid Wales, UK. Posts: 186	Commodore CBM 3032 'PET' just got hold of one of these which was dead apart from the screen, after changing all the caps it now shows some signs of life, I get the first full screen image of jumbled characters then a blank one before hanging on a screen with what looks like aliened exclamation marks at regular intervals vertically but only on the bottom half of the display, im sure its bad ROM and or RAM chips and have put on order the petvet from bitfixer but im am a bit out if my depth with this one, if anyone can give me any help or advice please get in touch, id love to get it working again and learn some very basic programming !! can provide photos if it helps Eddy

28th Apr 2015, 8:01 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Commodore CBM 3032 'PET' Have you searched online, a quick search turned this up, which may be completely unrelated of course: http://www.verrua.org/pet_repair/

28th Apr 2015, 9:30 pm	#3
stubbyeddy Pentode Join Date: May 2005 Location: Newtown, Mid Wales, UK. Posts: 186	Re: Commodore CBM 3032 'PET' thanks for that link, after reading that from what I can make out it has to be bad roms I can get hold of the roms online and the 2532 EPROMS but i dont have a eprom programmer ! can anyone help me out?

28th Apr 2015, 10:01 pm	#4
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,678	Re: Commodore CBM 3032 'PET' I've never worked on a PET, but on lots of other vintage microprocessor systems, and a fault like you describe would usually be a RAM fault. A quick Google suggests that the video RAMs may be 2114s, which are very often faulty in equipment of this age. The program RAMs are probably 4116 DRAMs which can also give trouble. Faulty ones often get hot, which is a good clue. The static RAMs (2114s) can often be diagnosed by 'piggybacking': just putting another (known good) RAM chip on top of the suspect one. If the fault is fixed, or changes, you know you've found something. The machine is clearly doing something - if it's clearing the screen, the CPU is running, so you can't be far off! Chris __________________ What's going on in the workshop? http://martin-jones.com/

3rd May 2015, 11:14 am	#5
acollins22 Pentode Join Date: Oct 2010 Location: Melton Mowbray, Leicestershire, UK. Posts: 156	Re: Commodore CBM 3032 'PET' I had a fault on my 4032 which prevented it coming up. The screen would clear and I heard a beep but nothing else. This was down to a faulty PIA chip on the IEEE interface. I pulled the chip and it booted fine. If you have a scope, take a look at the clocks and the _INT_ line. The faulty PIA was holding it down on mine. Circuit diagrams are out there and there is plenty of info. Good luck and keep us posted. Andy.