HP-67 Card Reader became very touchy

[Hiwi]

Hi,
measuring the elctronic parts on the board may lead to suspect results. Desolder one leg.
There are some issues witch zeners, this could be your problem as well.

I had one card reader with the the same issue and replaced the 2,2uF and 6,8 uF on the cardreader PCB. There are two 22uF in series with the read/write heads, but i never had problems with these.

The speed should be independend from supply voltage. (it has a timer) So I would not modify R1, try to adjust the exenter of the shaft first. Measure the current, it should be increased about 200-240mA when reading at 5.5 Volts.

Some people fix the clutch with CA glue, this is not the best solution it may lead to a rough drive noise, there should be a bit play / movement. Is the card pulled evenly? May be the rubbers / silicone tube is deformed minimally.

And yes many worm gears are a bit deformed by pliers, this was made to strengthen the clutch a bit. This was made from the factory and during service and should be normal.

Check the ribbon cable to the cardreader and solderjoints on the main PCB (CRC Chip) and the sensor chip on the reader PCB.

And do not let them make you crazy regarding the capacitor values. The tolerance is 20% and an
ESR up to 2 Ohm is ok. So your 76 uf and 26 uf are perfect!

And clean the contacs of the Reader thoroughly with alcohol.

If the contacts are dirty, higher voltage leads to more current => errors.

Inspect especially the write protection contact. I had some issues with it.

Ralf