Commodore CBM PET 2001-32B Keyboard
|by Bill Degnan
- 11/03/2017 20:16
The system boots but other than the "u" key and the "Enter" key the keyboard does not respond to keystrokes. I took apart the keyboard. The circuit board tests OK and the keyboard logic is OK (tried a different keyboard). The computer itself is fine. I have informally thus isolated the problem to be the black carbon tips that touch the circuit board upon a tap of a key from the keyboard.
I have heard one should paint/brush a metallic paint onto these tips, but I am thinking there must be a way to restore the conductivity without adding paint, something that will lead to issues down the road. I have also seen a page stating the solution is to scribble on the tips with a pencil. Also not to me a good long-term solution.
Would it make sense to simply use a pencil *eraser* on the tips instead, or a very smooth sandpaper/file to buff them in order to clear off a thin layer/film that may have formed?
I searched the web, surprised to have not have found more written about this. Up to this point I have had spare keyboards and this issue never came up. Time to experiment!
UPDATE: Got a tip from the CBM-Hackers mailing list to try "Keypad-Fix", a product that one can buy on Amazon. It's made for restoring conductive tips found in TV remotes, basically the same thing as the CBM keyboard issue here. I ordered a kit.
OK..I got impatient and took some graphite powder to the keyboard's conductive pads and it worked perfectly. One application and every key snapped back to life.
CAP C16 Missing, why?
|by Bill Degnan
- 11/17/2017 13:04
Got this message, posting for future reference:
VintageComputer.net Inquiry Contact Information Name: J Walter Hawkes
Email: --- Phone: --- ------------------------- Comments:
In regards to blog post titled Commodore CBM PET 2001-32B Keyboard :
Hey there Bill - I'm a member of the VCF list. Quick question: I'm noticing in your picture of the motherboard that C15, a tantalum cap near a power transistor, is missing... I have two 4016s I just picked up. One of them has that cap broken off. On the 4016 it's a 1uF 35W cap.
1. I'm guessing it's a coincidence, but I can't imagine anyone would remove it on purpose?
2. I'm about to order some of them and would happily send you one no problem no charge :)
I have some of that cyber clean here in the house somewhere...I may try that.
Thanks for posting and for sharing on the list. I'm diving into a PET for the first time...
Note the 4016 is not the same board as the 2001-32, but here are the approximately same locations on the motherboard, note how the 2001 board has a cut off cap on C25 (or is that C15? need to check the schematic). The question is whether this is a field repair recommendation from an old Tech Topics issued to repair shops or the cap broke off at some point. Either way, the machine works fine. I need to determine why it's missing before I replace it.
2001-32B missing C25 (or is that C15?)
External Cassette Short
|by Bill Degnan
- 02/02/2018 22:58
NEXT - trace the fault and repair. Because TAPE 2 works fine, the electrical fault is probably isolated to the cassette TAPE 1 5V circuit. At least I'd say that's the first thing to check.