HP-41CV power problem

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HP Forum Archive 21

HP-41CV power problem
Message #1 Posted by Don Davis on 10 Oct 2012, 6:46 p.m.

I have an HP-41CV exhibiting a strange problem. First, it is difficult to turn on. The on key must be depressed several times, perhaps even holding it down for a few seconds. I suspected this was simply a contact problem - however, once it is on, it powers off by itself after about 10 seconds. New batteries, memory clear, and no flags set. Any advice is appreciated. The power button problem has been there for a while, but the auto-power-down problem just came up.
Thanks, Don

Re: HP-41CV power problem
Message #2 Posted by Bruce Larrabee on 10 Oct 2012, 7:03 p.m.,
in response to message #1 by Don Davis

There is a capacitor on the mother board that can cause this problem. The capacitor is designated C2 and the long and short of it is that if your display driver assembly is covered in epoxy the you use a 470 pf cap and if it is covered with a plastic cover you use a 0.01 uf cap. Check that you have the right cap and that it is good.
The following is from the service manual.
There are differences in appearance as well as in the automatic (10 minute) time-out featUre. This is primarily due to a change 1n ~ capacitor of the logic board from .01 uf to 470 pf .
Revision "G" uses 470 pf/D160-057l
Revision "F" uses .01 uf/0160-3914
The difference in appearance can be seen by looking at the covering over the display hybrids.
Revision "G" is covered by epoxy .
Revision "Fit is covered by a plastic cap .
If the value of capacitor is interchanged with revi sion of the display driver assembly the following symptoms occur:
1. Revision "Gil with 470 pf
Frequency = 8.3 KHZ
Timeout = 9 mi nutes
Display = OK
2. Revision "G" with . 01 uf
Frequency = 435 KHZ
Timeout - , •
Display = fli ckering
3. Revision "F" with . 01 uf
Frequency = 6.3 KHZ
Timeout - 12 minutes
Di spl ay = OK
4. Revision "F" with 470 pf
Frequency - 110 KHZ
Timeout - 40 seconds
Display - OK

Re: HP-41CV power problem
Message #3 Posted by Don Davis on 11 Oct 2012, 9:13 p.m.,
in response to message #2 by Bruce Larrabee

Bruce, Thanks for the detailed response. Don't know when or if I'll have the time to take this thing apart and fix, but I'll know what to do then thanks to your good work.
Best regards, Don

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