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Full Version: HP-71B Card Reader Failure
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Symptoms: R/W Error after timeout.

Responds to commands (CAT, COPY TO, etc) but after hitting ENDLINE to pull cards, the reader does not respond. Then it will timeout.

Have you pulled the cleaning card through it? Make sure the contacts are clean on the card reader and the 71B. Do you have a known good card to try to read?
I tried DeOxit on the contacts. I'll give the cleaning card a try. I do have a good card that reads on a second reader I have.
Yep, these are buggy.

I have two, one reads and writes 90% of the time, the other is hit and miss. I did some numbers on the second one an it was around 30%.

Used the cleaning card, used deoxit on the contacts. Maybe the reader head is magnetized? I have a demagnitizer but have not tried it on the buggy one.

Didn't tape recorder heads need to be demagnitized on occasion?

(03-06-2016 10:11 PM)Geoff Quickfall Wrote: [ -> ]Didn't tape recorder heads need to be demagnitized on occasion?

Audio tape heads required periodic degaussing. Digital tape heads not so much. I still use my Realistic 44-232 Bulk Tape Eraser which can be found for $20 on eBay. It works on floppy discs and CRT screens, too.

Even submarines and aircraft carriers need to be demagnetized.

I have demagnetized items with a big 250 watt soldering gun, taking care not to burn anything with the tip.

(note the magnetic field is around the transformer, not the tip) And slowly drawing the gun away from the item works, and is a handy trick if you have a soldering gun and no demagnetizer at hand.

I've also used a soldering gun transformer for a transducer for an AC ammeter. Wire low resistance secondary with load. Put ammeter on primary leads. You'll need some way to calibrate it, IOW, translate whatever reading your seeing on your ammeter to an actual measured amp reading on the secondary load.

Caution, open terminals on transformer primary can develop EXTREMELY high voltages.
Has anyone ever seen a schematic for this reader?
(03-08-2016 12:14 AM)aj04062 Wrote: [ -> ]Has anyone ever seen a schematic for this reader?

While designed for the 71B, the card reader was first used on the HP-75 (HP Journal July '84). A circuit description can be found starting on p.2-17 of the HP-75 Service Manual.

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