hp 82104A only reads 67/97 cards

[John Garza (3665)]

Good point Ray - since the leaf switches were touched, the response changed - so that's the likely culprit. And yes, by 'leaf switches', I mean the thin metal strips that 'bow' upwards to make contact with gold pads on the PCB. 'Leaf switches' is what we used to call the similar structures in the HP-67/97 card readers.

So I disassembled again; and this time scrubbed with deoxit. Now I'm reading my HP-67 cards again, and the 41C cards no longer show MALFUNCTION, but instead I get CHECKSUM ERROR. Which, I think is a 'lesser' error if there is such a thing. Cards written by this card reader also receive a CHECKSUM ERROR when loaded on a known good card reader. And cards written with the good reader still show CHECKSUM ERROR when loaded on the faulty unit. And again I tried 360 degrees on the eccentric axle in 45 degree increments with 2 reads each. The midpoint of my good reads on the 67 cards was with the little plastic 'dot' on the axle head pointed 'downwards' (towards the back of the calculator). This is also where I receive CHECKSUM ERROR on 41C cards. When I rotate the axle away from this point by 90 degrees or so either way, I start to get MALFUNCTION or CARD ERROR.

I also salvaged a little crumb of the dried goo and checked it with my HP-3476B meter. The stuff is definitely an insulator.

-John