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HP41CV drains battery. Schematics? - Printable Version

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HP41CV drains battery. Schematics? - Harald - 03-18-2012

I have just opend one of my HP41CVs. It shows a strange behaviour. It will only run on batteries that are nearly flat. Otherwise it will draw a lot of current and drain them, but not power up. It then needs to be left for several days before it will power up again even on flat batteries. (I suspect a reset problem here)

I downloaded the schematics from Warrens website, but to my surprise found the board to be different. For example the reset transistors are nowhere to be found. Also I don't understand how the power supply works. I was expecting to find a switched mode power supply somewhere, but didn't. How does the battery charging work?
Does anyone have a schemtaic for the apparently different 41CV I have?

Cheers,
Harald


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

Could the power supply be integrated into the LCD driver chip? Seems strange, but it very much looks like it.


Re: HP41CV drains battery. Schematics? - Andres Capdevila - 03-18-2012

Hi,

Power supply is done by IC U2 and associated components in a normal HP41C.

Best regards.


Re: HP41CV drains battery. Schematics? - Andres Capdevila - 03-18-2012

BTW, I have a copy the HP41C/CV/CX service manual in PDF format (about 30MB), just let me know if you are interested.

Best regards.

Andres.-


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

I now suspect it is the display controller (not the IC on the mainboard which appears to be the power supply controller), but the actual display controller behind the display) that is casuing the problem. I have swaped the main board with another 41CV and the problem stays with the display and keyboard assembly. Has anyone had a broken display controller before?


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

If I may... I am interested!

Can you send a copy to

linux_lcv (at) yahoo dot com dot br ?

Thanks.


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

Hi, Harald.

Is there a way to post a picture of the mainboard?

Cheers.

Luiz (Brazil)


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

This is the PCB from the faulty calculator:

And this is from the working one:

But as I said, I don't belive the problem is on this board. When I swapped it with another calculator, the problem stayed with the display and keyboard.

Edited: 18 Mar 2012, 4:45 p.m.


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

HI.

Have you checked if there is any kind of short-circuit between any circuit lines of the keyboard? There is also one fact: the first picture (top-to-down) shows a more recent PCB, while the second one shows an earlier version. Chances are that the LCD's are different. It does not explain the high-current drain, and a faulty LCD controller might be the best guess.

Chances are you will easily find a replacement in Europe (you are in German, right?). I have at least one good LCD driver with a broken LCD, so if you are not that lucky finding a replacement, contact me and I'll find a way to send it to you. It is fairly easy to replace the LCD in the LCD module (LCD+drivers assembly).

Cheers.

Luiz (Brazil)


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

Quote:
Have you checked if there is any kind of short-circuit between any circuit lines of the keyboard?

I can't find anything there.

Quote:
There is also one fact: the first picture (top-to-down) shows a more recent PCB, while the second one shows an earlier version. Chances are that the LCD's are different.

I don't think they are different. I got the other main board to work in the good calculator. And briefly the other way round too. But once I take the battery out and put it back in, the calculator draws a lot of current and doesn't appear to turn on.

Quote:
It does not explain the high-current drain, and a faulty LCD controller might be the best guess.

Chances are you will easily find a replacement in Europe (you are in German, right?). I have at least one good LCD driver with a broken LCD, so if you are not that lucky finding a replacement, contact me and I'll find a way to send it to you. It is fairly easy to replace the LCD in the LCD module (LCD+drivers assembly).


I think it must be a problem with the LCD driver.

How can I disassemble the display? Is it possible to leave all the heat stakes of the keyboard in place? I can have a look on ebay for a broken HP41. If you want to sell your broken LCD with the good driver, I am sure we can agree on something.


Re: HP41CV drains battery. Schematics? - Andres Capdevila - 03-18-2012

Hi Luiz,

You should be able to download it from here:

HP41 Service Manuals

Regards.


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

Thank you!


Re: HP41CV drains battery. Schematics? - Harald - 03-18-2012

Quote:
How can I disassemble the display? Is it possible to leave all the heat stakes of the keyboard in place?

All that is explaind in the documents Andres posted!


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

Many thanks! I appreciate!

Luiz (Brazil)


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

HI.

You may also find some extra pictures of the HP41 LCD being disassembled here. Almost all of them were made with a picture scanner (I had no digital camera back then). Hope it helps a bit more.

Cheers.

Luiz (Brazil)


Re: HP41CV drains battery. Schematics? - Luiz C. Vieira (Brazil) - 03-18-2012

HI.

I would neither charge you for the LCD nor the posting, don't worry. But I am pretty sure you'll find something closer to you. If you really canĀ“t find anything in the next days let me know.

Cheers.

Luiz (Brazil)