HP67 repair - help identify capacitors

[Hiwi]

Hi,
i have repaired many HP-67, many :-)
I do not recommend to replace all caps without understanding their function.

If you have test equipment you can measure the ripple.

Replace the big yellow cap on the mainboard, it is a 47uF tantalum, then the brown one, it is 22uF.

If you have a cap tester and see a great Vloss, replace it, if it is under 1%, put it back.

Use only tantalum caps.

But in most cases the caps on the cardreader PCB are the problem. There are different versions.
On your board there are axial tanatalums 2,2uf, i bit hard to get and expensive.
The cap across the motor never fails :-)

Do not buy NOS from ebay, they are often 20+ years old. Digikey or Reichelt have them in stock.

And try following:
1.) Write a card with some code.
Try to read in another cardreader (67,97 or HP41)
Does it read sucessful? => there is a great chance, that the problems are the caps.

2.) Supply a voltage so that the battery indicator comes up, at about 3.2 volts.
Try to read a card. If it works => in most cases cap problem.

Does not? Could be a greater problem with the signal controller (does the card stop correct? if not may be cleaning of the contacts may help)
or the CRC Controller on the mainboard, but this happens not often.

Did you check the speed? On your PCB, there is no poti to adjust the speed, so it is fixed.The
service manual advices you to change a resistor on the pcb. But do not replace anything here.

If you have replaced the roller the diameter may not be exact and correct.
The white (on early HP67s, otherwise black) axle (for the spur gear) is not straight, it is slightly bend so you have to adjust the
pressure the card is pressed on the head. This has influence on the speed as well.

Try to play around a bit.

If you can measure the current while reading, adjust the axle so that the meter is reading 200mah at 3.8 volt.
Ralf