HP-82104A Card Reader Repair Questions

[Papymouzot]

Hello everybody,

no one has any advice to give me in order to repair my card readers ?

charles

[teenix]

(03-28-2024 07:43 AM)Papymouzot Wrote:  Hello everybody,
no one has any advice to give me in order to repair my card readers ?
charles

I'm sure there is someone who can help. Unfortunately, the card reader is a fairly complex setup having its own ROM and interacting with a host calculator, so anything aside from a mechanical problem or a dud capacitor may prove to be a difficult fault-finding task requiring some test gear like an oscilloscope and some knowledge of its operation. I have to admit, I tried and failed to repair one.

cheers

Tony

[Papymouzot]

Hi Tony,

I have a few « tools » including an oscilloscope. I have done little electronics in the past and I have as a hobby electric trains N scale and I often play with the soldering iron on tiny tiny parts ??

Caps have a very bad tendency to wear overtime, and 44 years later most of them are likely to be out of service.

I recently had to change the caps inside the battery pack at the same time I changed the batteries to NiMH new ones. The 100uF was completely dead. Next pack will be modified to have a usb c charging circuit.

I would love to learn what can be said about the tests I conducted on the two card readers giving me the card err message, and what should be tested / modified next.

I would really appreciate to have some guidance on which caps to change first, their location and specs value/voltage. They won’t be easy at all to remove and if I can change the ones which may solve my problem first it would be great ?

Thanks in advance !!!!
Charles

[teenix]

Do you have a copy of the service manual?

https://literature.hpcalc.org/items/396

[Papymouzot]

(03-28-2024 11:26 PM)teenix Wrote:  Do you have a copy of the service manual?

https://literature.hpcalc.org/items/396

Hi Teenix,

I didn't read this manual thoroughly before. I just read it again, taking more time.

Thank you for mentioning it, I initially missed lots of valuable information, it gives me new test opportunities.

The document schematics are valid for the two older (1980) readers I have. The more recent ones (1985 & 1986) have different pcb layouts. If one knows where to find the same document for the later card readers I will appreciate it a lot. I could not find it on hpcalc.org

Thanks to the available service manual I have now a complete set of information on what caps are on the circuits with their values for two readers. I am going right now to source the three capacitors from the sense pcb and also for the logic pcb and psu just in case.

I will come back after receiving the items... unless somebody else has more advice, and I will respond asap

Thanks again all for your help.
Charles

[Papymouzot]

Dear All,

I wish you first a happy Easter break !

Then some news… I don’t know why but I really found useful to open the working reader to swap the card unit/1motor, with the electronics of another non working unit.

Result: I ordered the caps for nothing. The Card err message seems to be coming from the card/motor unit ???

The unit which is working is a bit sensitive though, I got scared when I reassembled it… I also had in a few occasions the card err message, but after 3/4 attempts I finally had « working » and subsequent tests of writing /reading worked fine.

Next… find why the card/units don’t work…. ??

Charles

[Papymouzot]

Easter update:

I opened the only card unit/motor I didn't open it before, just in case the pressure on the screws may change something. The card compartment looked clean, no residue from the gummy wheel. I cleaned the head with a cotton swab and isopropyl alcohol, put everything together and test again.... First tests, card err, but on the third attempt the card got read properly and it requested the second track.. it read the second track and the program was inside the 41. I tried writing the program to another card, did a "memory lost" and tried reading it again.... it worked. I hope this will last !!

I have now two readers working out of 4....

I was left with one giving "malfunction error" and one giving "card err".

I tried swapping the card/motor units and the error type is once again dependent on the card/motor unit and not the electronics. I really should have tried this swap game before... I only did it in between the two readers giving "card err" !

I opened the card/motor unit giving "card err" and cleaned it thoroughly although it was quite clean already. Put everything together, and I have something new.... depending of the position of the eccentric pin I get "no room" or "card err" but it can't be reproduced with precision for the same positions of the pin.

I have tried turning the pin a very little bit at a time, but I only get either no room, or card err... and yes, I checked the available program size... plenty of room available... and I have also tried with a working card reader, and the card /program was read without any problem...

I opened the card/motor unit which was giving "malfunction". and regardless what I try, I still get malfunction....

So definitely I made some progresses but I am still only 50% happy...

[teenix]

Just guessing, it might have something to do with an excessively noisy motor in the electrical sense and may be interfering with the sensitive head signals. C1 across the motor terminals might need replacing, or possibly the motor brushes are worn causing noisy operation.

cheers

Tony

[Papymouzot]

This can be tested, do you know the value of the cap on the motor poles ? Is this the same value as the c1 which is on the sense amplifier circuit ? 3.3uF 15v ?

[teenix]

(04-01-2024 09:45 PM)Papymouzot Wrote:  This can be tested, do you know the value of the cap on the motor poles ? Is this the same value as the c1 which is on the sense amplifier circuit ? 3.3uF 15v ?

Judging by the cap size on the motor it is probably similar.

cheers

Tony

[Papymouzot]

I am awaiting for the caps to arrive, I’ll post the results.

Disassembling the motor to check the brushes isn’t too difficult, but reassembling the motor is a challenge !!