HP-67 Card Reader became very touchy

[Hiwi]

Hi,
the marked capacitor on the PCB is the 3.3uF, the blue on the right is the 6.8uf
The big red ones are 22uf. They are in series with the read/wright coils. if the ESR is too high, or the value is not correct the signal may be too low or cut off.

I replace them always complete when fixing the reader.
C3 and C4 are connected to ground and what is their task?
They should stabilize Vss and VCC and supress ripple! Nothing else. So they are not that critical regarding the value.

Resolder them or change them. They are cheap. But new ones do not have always better ESR.

Don't bother to much with the ESR and values, as I have already told. I take for C3 and C4 values I have on hand, 4.7 or 10 worked for me in any case.

Try to get high qualtity tantalums from vishay or Kemet.

If you take the PCB apart remove the motor cables and look for the head cables, as they come off sometimes.

And cut the legs from the tantalums as short as you can. And resolder them with more heat, so that there is good contact under and on top of the PCB. The trough-holes of the pcb may be faulty. I do not use leadfree solder.

The capacitor on the motor (connected directly on the motor) is a 3.3uf as well. It is not critical. I replace it with something i have on hand. And this could be a 4.7 even an small electrolyt capacitor is sufficient.

Some people solder an extra tanatalum from pin 20 of the sense chip to ground. PIN 20 is VBB.

If you take off the PCB, clean the contacts thoroughly with IPA. The head as well, dry clean afterwards.

And test the contacts, may be the headswitch may be faulty:

Connect a multimeter to TP8 and insert a card by hand and test TP9,TP10 and TP11.

TP9 should turn on first then TP10 (if no writeprotected card is inserted) then TP11.
This is a very common fault! You can adjust this with the 3 screws. Remember the position, take a picture before.

And don't put to much tension to the screws of the PCB. In Germany we say: "Nach fest kommt ab" :-)

And did you measure the resistance of the head coils? Blue-Orange and Red-Yellow, schould be the same in both measurements.

Have you resoldered the CRC Chip on the main PCB?

Ok, any more does not occur to me now. :-)

Ralf