82104A Card Reader repairs


I recently acquired a non-working 82104A card reader for the HP41 and am attempting to restore it. Cards run through OK, but it can't read them - usually I get a "CARD ERR" message or occasionally "CHECKSUM ERR" (which usually leaves the calculator in a corrupt state). Writes seem to work as expected (with cards prompted), but since the cards can't be read back I have no way of knowing whether anything is actually being written to the cards. Any help on what to look for/repair would be appreciated!

More about the repairs so far - references used were:
"HP-41C Card Reader Repair The Short Fix Approach" by Mark Hoskins (Jan 2002);
"Repairing the hp 82104A Card Reader" by Dave the "lostrabbit" (May 2000).

First I repaired the infamous "gummy wheel" using the "Short Fix Approach", which bypasses separating the two halves of the card path. Upon reassembly the reader could now draw cards through OK, but could not read them. Suspecting more gunk inside I then dismantled the card path as per Dave's article. The read/write head and path looked clean (I re-cleaned them anyway). The two card wiper switches appeared to be correctly contacting the circuit board, and the two copper tensioning strips seemed properly located, though I don't know whether one that presses the card against the heads is correctly tensioned. I then re-assembled everything, but it still didn't work.

I have done the obvious mechanical checks, but have not electrically tested anything (yet). I've tried the reader on two 41CVs, and with previously written cards (both clipped and unclipped), with similar results. Any clues what else might be wrong?

Brian Ayling.

PS - I was amused to read that "pink" fuel line could be used to replace the gummy wheel, without any useful dimensions given. I found it needs to have an (installed) outside diameter of 1/4 inch or 6.3 mm.

Edited: 14 Mar 2004, 12:00 a.m.

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