PET 4032 keyboard scanning problem / was Re: Anyone have an image of a Japanese PET chrgen ROM 901447-12?

-----------------Original Message: Date: Mon, 05 Apr 2010 16:28:58 -0700 From: Brent Hilpert <hilpert at cs.ubc.ca> Subject: PET 4032 keyboard scanning problem / was Re: Anyone have an image of a Japanese PET chrgen ROM 901447-12? Speaking of early Commodore PETs, I have here a 4032 on which some of the keys do not work. Some time ago I took a brief look at it and, as I recall, concluded the problem was not the keyboard but rather something was messed up with the scanning, something like not all columns/rows being scanned. I think it was a 6821 or 6822 or some such doing the I/O, but the diagnosis was perhaps more suggestive of something like a PROM bit failure causing the firmware program to foreshorten the scan sequence. Anyone have knowledge of a known failure mode of this sort with these machines? --------------------Reply: The most common problem is just oxidation and/or wear of the rubber 'contacts' and the PCB grid; if you're lucky a good cleaning will clear it up, in case of bad wear of the conductive pads you may have to recoat them with conductive paint ot glue little pads of aluminum foil or aluminized mylar on to them. Electronically they are a normal scanned matrix, driven by a 6520 PIA (UB12?) and a muliplexer; if there is a problem there then it would most likely be with all the keys in a certain row or column. I suppose it's possible, but I'd be very surprised if it were a bad ROM. Check the schematic and you should be able to jumper across the appropriate keyboard lines to test all the rows and columns. http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/803202…