HP 67 drawing a lot of current when reading a card

[cncjerry]

I dug out my 65 and 67 on day 12 of a whole-house search for my 15C and 11C. My 67 worked fine last I used it, maybe 5yrs ago. The 65 works great with a so-so battery pack using the charger. Motor sounds good, reads fine, etc.

My 67 on the same charger and battery pack pulls the card about 1/4 inch and then I get the 'error' message. I notice that my 400ma Tektronix supply that it blinks the overcurrent light sometimes and then stops. Lately it seems to be running better. While on the Tek supply without the battery pack, the 67 draws 100ma. When I put a card in it, it draws around 380ma when it reads the card completely. It seems like it hits the 400ma limit sometimes on the supply.

So I'm wondering if a 380ma draw when reading a card is normal? it seems high compared to what I've read on this site and others.

Thanks

Jerry

[teenix]

I'd check the card reader for gummy wheel or dirt/corrosion in the mechanism. The high current may be from excessive motor load. If this is the case, the sense chip may not like the higher current.

cheers

Tony

[cncjerry]

Thanks, the reader was rebuilt by me years ago. I've repaired 6 or more calculators, both HP and TI, that read cards. I have a 65, 67, two 41s with readers, and three or 4 excellent TI 59s. My TI 59s look and work like new. Hard to believe how much they cost back then. My 67 is, or was, my favorite, but now it seems like it has a problem in the sense amp. I note it has a resistor above the sense amp on the board. It is labeled as 40ohm, but measures 53.37 in circuit. Dont know what it does in this circuit, but I will probably replace it with the proper value. The motor sounds like it is hitting a high spot on the wheel so I replaced the silicon tube that I've used in my repairs successfully. I've tried using o-rings but they dont seem to be as consistently round as the tubing I have.

Thanks for the reply.

Jerry

[teenix]

If the resistor is between pin 1 and 2 of the sense chip, it is for motor speed setting. I've never heard of a value that low. Generally between 4 and 5k.

cheers

Tony

[Dave1947]

You might check the 3.3uf capacitor on the back of the motor. It might be bad and shorting a lot of current.