Repaired 41C has short time-out

The Museum of HP Calculators

HP Forum Archive 15

Repaired 41C has short time-out
Message #1 Posted by Michael Burk on 14 June 2005, 4:49 p.m.

I bought a very cheap 41C that had several display anomalies. I took it apart and found that some of the leads to the display had come loose. I resoldered them, and now the calculator works great, except for one strange thing: the automatic shut-off time-out is very short - about 11 seconds! I read in the manual that it should be 10 minutes. I measured the voltage of the batteries, and they seem in normal range. Anyone have any ideas why this might be? Thanks!

Re: Repaired 41C has short time-out
Message #2 Posted by Raymond Del Tondo on 14 June 2005, 5:51 p.m.,
in response to message #1 by Michael Burk

Maybe a dissolved capacitor,
or a malfuntional chip on the CPU board,
maybe a timer?
Raymond

Re: Repaired 41C has short time-out
Message #3 Posted by Eric Smith on 14 June 2005, 8:52 p.m.,
in response to message #1 by Michael Burk

IIRC, the service manual warns about an incompatability between some revisison of display components and others, which can lead to the described problem. I don't have my copy of the museum DVD at hand to check the details.
So possibly your calculator has already been repaired improperly, which would also explain the poor solder joints.

Re: Repaired 41C has short time-out
Message #4 Posted by Randy on 14 June 2005, 9:30 p.m.,
in response to message #3 by Eric Smith

It's not uncommon for the solder joints on the LCD driver to fail after twenty years of being dropped and fumbled.
The short auto shut off time can usually be resolved by cleaning the logic board well with isopropyl alcohol and drying well before reassembly. Make sure you clean your resoldered connections as well since it's usually residual flux contamination of some sort or crud on the board that will cause any number of problems. When you're dealing with nano and micro amp levels, it doesn't take much in the way of cooties to cause problems.

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