41CX board does not power on

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41CX board does not power on

Postby syrou » Fri Dec 30, 2016 11:49 am

Hi all,

A while ago I bought from eBay an HP-41CX main board (as-is state) to upgrade my 41CV one on my fullnut calculator. This is the board version I bought:


However after replacing it I observed that it does not power on at all. I have a basic knowledge in electronics, so the first thing I did was to desolder and inspect the electrolytic caps in case they had dried out (elevated ESR). But they were perfectly fine. From this point onwards, I don't know how to continue the troubleshooting process. Particularly complicated is the process of measuring voltages due to the way the calculator is assembled (it needs to be closed so batteries make contact with the main board).

Any idea of other potential culprits?
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Re: 41CX board does not power on

Postby Drulli » Sat Apr 15, 2017 4:05 pm

there can be hundreds of problems with the board.
No 1 for me to check is always whether there is a proper connection via the zebra strips. The connections only work fine if upper and lower part of the hp41 can be screwed together tightly.
For that all screw post needs to be in good shape. Very often they are not, i.e. when you opened the CV, it always can happen that little fractions impact the stability.

On your photo I saw that the "upper" solder joint of the Schottky Diode CR5 (the device at the right side of the beeper connection) looks pretty bad. Give it a try and put some fresh solder on.

Otherwise check the components, Restistors, Diodes, etc.

One question: Are you sure that you can interchange CV mainboard with the CX mainboard without running into compatibility problems?
The display driver is still the same (in the LCD part of the calculator) and has to work with the CPU and several ICs. The TImer IC in the CX has a connection to the display driver, in the CV naturally not.

Good luck in any case!
HP-41 CX, HP-41CV, Printer 82143A, Cassette Drive 82161A, PILbox, 82104A Card Reader, MAth I, Circuits I
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