Repair HP41CV. Help needed.

[Kees van der Sanden]

The LCD of HP41CV will not turn on.

I measured the following behavior:
When applying a battery voltage of 6 Volt, the calculator sinks 340 uA. (This current seems much too high for the sleepmode).
When the ON key is pressed, the supply current goes to 1.4 mA.
When the ON key is pressed, the battery current is 2.2 mA.
The calculator cannot be turned back to the sleepmode by pressing the ON key. By reconnecting the battery, the sleepmode is back.
The internal supply voltage is in sleepmode about the battery voltage and in active mode 6.4 Volt, regardless of the battery voltage (between 4V and 6V).

The model is a halfnut version, serial 2721Sxxxxx.
Is this a known problem?
Where to find service documentation for this model?

[Rik Bos]

Hi Kees,

Did you check the board connection (small gold wires or conducting rubberstrips) and did you checked the board for whiskers (small conducting parts).
If you're shure it's a hard ware problem start with replacing the tantalium caps, the costs are low and the change of succes is high.
If you have the diagrams from the service manual you can check the power supply with a scoop.

-Rik

[uhmgawa]

Quote:

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The LCD of HP41CV will not turn on.

I measured the following behavior:
When applying a battery voltage of 6 Volt, the calculator sinks 340 uA. (This current seems much too high for the sleepmode).
When the ON key is pressed, the supply current goes to 1.4 mA.
When the ON key is pressed, the battery current is 2.2 mA.
The calculator cannot be turned back to the sleepmode by pressing the ON key. By reconnecting the battery, the sleepmode is back.
The internal supply voltage is in sleepmode about the battery voltage and in active mode 6.4 Volt, regardless of the battery voltage (between 4V and 6V).

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Can you get a scope on the LC oscillator tank when trying
any/all of the above? Check frequency, stability, and
oscillator startup time.

Quote:

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Where to find service documentation for this model?

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I've found it in various forums. However the only response to
your question which apparently won't get this post censored is
to recommend you buy the museum DVD.

[Kees van der Sanden]

Thanks for you reply.

I probed with a scope on a lot of tracks.
Except for DC levels I traced one repeating clock pattern close to the display pins.
The clock pattern starts with 8 pulses at a frequency of about 500 Khz.
Next this burst remains at a high level (about 6 Volt) for about 10 us.
Finally the signal changes in a damped sine.
This patterns repeats itself continuously.

I think I need the service documentation to continu.

[Ronald P]

You have a PM

Ronald