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HP Forum Archive 13

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Dead HP41CX
Message #1 Posted by Ben Moss on 3 Aug 2003, 12:27 a.m.

Ok, I just got my new HP41CX to work today (look down a couple of threads). I was using a power supply at my university's radio club shack to test it. Right after I got the battery pack to work, a friend of mine walked in and I showed it to him. He looked at the modules, and before I could stop him he said "Wow, look at these!" and pulled one out while the calculator was turned on. According to the manuals, this is a Big Fat No-No.

The calculator seemed to work immediately afterward; I tried some basic math like 3+3 and it gave the right answers. I put it away, and now when I try to turn it on, nothing happens. I know it isn't the battery because I have tried it with the power supply as well.

So, either the calculator died from having the module removed while it was on or it died from me playing with batteries and whatnot. I was very careful with the batteries to never reverse the polarity or give it too much voltage but it's still a possibility. What's the prognosis?

Again, many thanks.

-Ben Moss

Re: Dead HP41CX
Message #2 Posted by Hans Brueggemann [GER] on 3 Aug 2003, 4:25 a.m.,
in response to message #1 by Ben Moss

ben, i never ever saw an hp41cx being killed by just *removing* modules during operation. most likely, your calc has the typical 'foul keyboard contact syndrome' or 'battery removal amnesia'. the doctors in this forum already wrote a lot about that topic. just dig through the archives.

cheers, hans

Re: Dead HP41CX
Message #3 Posted by Randy Sloyer on 3 Aug 2003, 10:25 a.m.,
in response to message #1 by Ben Moss

In you have it open, try a hardware reset to clear memory:

Just short out the biggest capacitor on the logic board for a couple of seconds. It should be 470 uf at top left on fullnuts and to the left of the cpu on halfnuts.

If it's not open, hold down the backspace key, press the on button and release the backspace. You should see MEMORY LOST.

41's are pretty hard to kill.

It works
Message #4 Posted by Ben Moss on 3 Aug 2003, 5:10 p.m.,
in response to message #1 by Ben Moss

It works again! Thank you so much for your help.

I had tried twisting the calculator a little, pressing under the display, and applying pressure in various places. None of that helped. Pressing various combinations of backspace/on (and all other combinations listed in the repair guide) didn't do the trick either - it was the 1" drop that fixed it. I guess one of the internal connections got messed up while I was playing with the battery pack.

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