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HP Forum Archive 13

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Message #1 Posted by Jon on 1 Aug 2003, 3:19 p.m.

Long time ago I posted the problem I had with the HP-67. It writes but doesnīt read. The problem should be a capacitor. But this unit hasnīt the capacitors described normally. It has three silver cylindrical capacitors in the card reader circuit. So I decided to replace all of them for tantalum capacitors. I have seen they are 22uF, 22uF and 15uF. But once re-assembled nothing changes. It writes but doesnīt read. Any idea???

Thanks in advance


Message #2 Posted by Vieira, Luiz C. on 1 Aug 2003, 4:56 p.m.,
in response to message #1 by Jon

Hi, Jon;

once we had a problem in one 82104A, the HP41 card reader (belongs to Gordon Dyer), that was detected as being the magnetic head with an open circuit, one of the coils had a broken wire. I am not sure of what procedure was taken by Gordon to identify the problem, but if one of the wires measures too high resistence to any of the other four, then you found it.

I'd guess an operational amplifier could be the "bad guy", but I do not know the card reader's circuit. I have an HP97 and if I am not wrong, the card reader in both of them is slightly different. What I can tell is that depending on the analog parts of the circuit, you may have an operational amplifier that works fine in a pre-defined gain and current conssumption (e.g. recording) and cannot keep the expected performance in another situation (e.g. reading).

Anyway, based on previous posts, I am taking a lot of care not inducting owner's to search for problems that are hard to be the cause, so I'd also suggest searching for bad contacts, head cleaning, contact strips alignment...

Oh, yes, in time: when I received the HP97 I have it was not able to read or write. At the moment it was switched to ON the card reader's pulling motor started to work and after about three to four seconds it stopped. I checked to see that all metal strips were in contact with their equivalent tabs, as if there was a card already inserted when it was switched to ON. I saw three screws above the metal strips and I adjusted them in a way the strips were close enough to their tabs without touching them. Since then it works perfectly fine, all functional. I don't think this is the same that happens with yours, but you see: the problem was much more simple than short circuited motor drivers, bad connections, controllers, etc. Only adjustment.

Hope you succeed repairing it.

Luiz (Brazil)

Edited: 1 Aug 2003, 4:59 p.m.

Message #3 Posted by Gordon Dyer on 1 Aug 2003, 8:05 p.m.,
in response to message #2 by Vieira, Luiz C.

You are right Luiz. My card reader had an open circuit coil.
The coil connections are:
Red - Yellow is coil 1
Blue - Orange is coil 2
Black is a screen

You should measure (with a DVM) about 35-40 ohms for each coil and about 1Kohms between coils and the screen with them plugged into the circuit. If they are unplugged then you should measure open circuit between the coils and the screen on a 2Mohm range.
I am relying on memory for the values so don't think they should be accurate!

Message #4 Posted by David Smith on 2 Aug 2003, 3:56 p.m.,
in response to message #1 by Jon

I had an 82104A reader for the HP41 that had a motor wire too close to the head. It did the same thing. Another possibility is a bad reader chip.

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