Search Posts:

Commodore CBM PET 2001-32B Keyboard


Return to Threads

  Commodore CBM PET 2001-32B Keyboard by Bill Degnan - 11/03/2017 20:16
The Commodore CBM (PET) 2001-32B, after restoration. Click image for larger view.

After years sitting on top of a dryer in the laundry room, the entire motherboard became covered by lint dust. This photo shows some dust removed, revealing a pretty serviceable circuit board with little rust. Click image for larger view.

Keyboard Repair

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.

Time has not been kind to the keyboard contacts. This photo shows the keyboard removed from the chassis. Click image for larger view.

Keyboard partially disassembled. I desoldered the caps-lock wires temporarily in order to remove the circuit board from the keyboard key housing. Click image for larger view.

Closeup view of the keyboard contacts. I have cleaned the contact tips with 91% isopropyl alcohol and that had little effect, only a few more keys respond. I speculate a glaze has formed on the tips and the conductivity has been lost.
Click image for larger view.

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.

My daughter used a Cyber Clean cleaning compound to clean the motherboard up nicely.
Click image for larger view.

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.

Pictured above is the wire extension I installed onto the caps-lock switch connection points so it will be easier to work on the keyboard in the future, should the graphite eventually need to be redone. Click image for larger view.

And another Commodore PET 2001-32B is brought back to life. Click image for larger view.

More photos

  CAP C16 Missing, why? by Bill Degnan - 11/17/2017 13:04
Got this message, posting for future reference: 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.

4016 mobo
2001-32B missing C25 (or is that C15?)

  External Cassette Short by Bill Degnan - 02/02/2018 22:58
Tape 2 internal Commodore PET cassette port
Because the external cassette port is not responsive (no power) I used the internal cassette port to load a cassette program, located near where the power connector attaches to the motherboard from the transformer. The internal port is called TAPE 2. Click image for larger view.

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.



Buy a Commodore Computer Poster

Popular Topics and FAQs

  • Commodore B Series Tips and Tricks
  • Aerocomp TRS 80 M 1 Expansion Unit DDC
  • Items Wanted
  • Lobo Max 80
  • Zenith Z-19-CN
  • Prototype PET 2001 photo
  • Using Toggle Switches to Analyze Memory
  • Commodore Disk Archive Project
  • PET 2001 Prototype at Gametronics 1977
  • Jim Butterfield Photo
  • IMSAI 8080 With Processor Tech. Cutter
  • Secrecy is the keystone of all tyranny
  • Cromemco System Three
  • Northstar Horizon - Boot Problem
  • Computer History and Restoration Links
  • Commodore BX-256-80 - 8088 Co-processor
  • S-100 board testing with Z-80 ICE
  • Donner 3500 - an early portable computer
  • Digital (DEC) PDP 11/05 NC Assembly
  • Univac 1219 rescue
  • Fido BBS listing node list 6-13-1986
  • PDP 8e
  • MITS 88-2 SIO (2SIO) for BASIC
  • Visual Technology Inc Model 1050
  • Amiga 2500 Restoration
  • The Evolution Of IBM Computers
  • Replacement teletype print hammer head
  • Archiving and Copying Software 101
  • Computers Built 1940 - 1950
  • CBM B-520 (a.k.a B256-80 or B500 256)
  • RCA COSMAC Microkit
  • Commodore 64K C-116 Mods
  • MITS 8800b Turnmon 9600 baud
  • Catweasel, 8in and 5 1/4
  • Raspberry Pi as Gateway to Internet
  • Digital PDP11 late 1969 early 1970
  • PDP 11/40 72 inch cabinet model
  • PDP 11/40 Industrial 11 model
  • Digitial MicroVAX 3100 30 System
  • Digital VAX 4000-200
  • Commodore 64 / 1541 DRIVEKNOCK
  • Booting the System Using RL02 drive
  • PACS: Reflections by Kathleen Mauchly
  • Tele-Graphic Computer Systems Inc.
  • Commodore B Series SID Jukebox?
  • Installing Core into PDP 11/40
  • Setting Up OpenVMS 7.1 DNS CLERK
  • Felt-Tarrant Comptometer Model J
  • NextStation Color
  • Digital Rainbow (PC100-B2)
  • 1970 Compusad Compulogical Tutor
  • Archiving Papertapes Using DSI NC 2400
  • 1976 P.C.C. Features the MAI JOLT 6502
  • 1961 Beckman DEXTIR Computer
  • UNIVAC 1 and UNIVAC File Computer 1
  • Past Issues:

    MicroWorld 9 76

    This image was selected at random from the archive. Click image for more photos and files from this set.