The Museum of HP Calculators

HP Forum Archive 17

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HP 41C premature turn off
Message #1 Posted by Ron on 13 June 2007, 11:47 p.m.

G'day,

I have an HP 41CV that has developed the nasty habit of automatically turning off prematurely. Instead of waiting 10mins it turns off at any random time between 10 seconds and 10 minutes.

On the assumption that the problem might lie with a leaky capacitor I have swapped the electrolytic capacitors with new ones and even tried tantalum caps but to no avail. Does anyone have a solution for this irritating behaviour?

Also on the PCB there is a device resembling an electrolytic capacitor encapsulated in unlabled grey heatshrink. The device appears to be slightly waisted as might be the case if you applied heatshrink to a bobbin. It is about 10 mm long and about 6 mm Dia excluding the leads. It has two leads exending from one end. Does anyone know what this device is?

Cheers, Ron

      
Re: HP 41C premature turn off
Message #2 Posted by Diego Diaz on 14 June 2007, 3:28 a.m.,
in response to message #1 by Ron

Hi Ron,

Please check this previous thread in this forum, it may help. ;-))

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv017.cgi?read=113311#113311

Cheers.

Diego.

      
Re: HP 41C premature turn off
Message #3 Posted by Randy on 14 June 2007, 10:06 a.m.,
in response to message #1 by Ron

Quote:
Does anyone know what this device is?

That would be an inductor in the PSU. Nothing at all to do with your turn off problem.

Thoroughly clean both sides of the logic PCB sides with isopropyl alcohol. Let it dry well before reinstalling. Various cooties and flux are the main cause of premature turn-off.

      
Re: HP 41C premature turn off
Message #4 Posted by colhind on 15 June 2007, 11:43 p.m.,
in response to message #1 by Ron

Thanks everyone. Problem solved. It was due to poor contact between the printed circuit boards and the conductive rubber sandwich strip.

Should have guessed this as I have had trouble with similar devices that make the connection between LCDs and PCBs.

Yes I also think it is an inductor of some description but I was afraid of damaging the coil so didn't opt for removing the heatshrink.

Cheers, Ron


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