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HP Forum Archive 14

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HP67 Card reader
Message #1 Posted by Charles on 9 Feb 2004, 7:05 p.m.

Another one !

I also have a 67 which worked as a calculator but the card reader didnít work at all. I changed the "gummy" wheel and it pulled the card through but didnít read it. The action was a bit jerky so I took it apart again to check the clutch but 3 of the 4 red and black wires between the motor and bridge PCB became disconnected. Can anyone help with the order in which they should be reconnected ?

The two centre wires seem to be the black (one is still connected) while I think that the outer wires are the red ones. Iíve traced these back to the external power supply plugs. Looking at the calculator lying face down, one red wire comes from the left bottom round plug (this in turn is connected to the battery supply) while the other red wire comes from the right plug. Looking at the bridge PCB from the top (chip) side, which way do they go ?

Could the magnetic head also be faulty ? The clutch seems to be OK.

Thanks again for any help Charles

(p.s. Perhaps I should give up trying to repair these !)

      
Re: HP67 Card reader
Message #2 Posted by Randy Sloyer on 10 Feb 2004, 12:02 a.m.,
in response to message #1 by Charles

Starting from the top of the board, wires on left side, chip on right:

  • Battery Red
  • Battery Black
  • Motor Black
  • Motor Red

You can check the head for open circuits, there are two windings, each measure about 50 ohms. Courtesy of Tony Duell:

Head wiring colours:

  • Blue = HA ) Track A winding
  • Orange = HAC )
  • Red = HB ) Track B winding
  • Yellow = HBC )
  • Black = ground

Be sure the head surface is VERY clean. Units that seem to have a lot of oxidation and are dull I give light polish with 2000 grit carbide paper then re-clean. It's fixed more than one dodgy card reader for me.

      
Re: HP67 Card reader
Message #3 Posted by David Smith on 10 Feb 2004, 12:39 p.m.,
in response to message #1 by Charles

Readers that write but do not read are a very common problem. The cause is a bad little blue dipped tantalum filter cap on the reader circuit board (usually located at the top end of the reader chip... but some layouts are different). The tantalum caps on the read windings (usually yellow) do not seem to fail.


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