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I just fried two HP-41s?
03-26-2021, 06:11 PM
Post: #1
I just fried two HP-41s?
Yesterday my 41CL just stopped working while I was using it. So I recharged the battery and let it sit overnight. I tried to insert the battery again and no go.

Today I took a new 41CX and swapped batteries between them. It did not help and the 41CX made a single BEEP at power on and now it is dead too.

Now I wondered if the NiMH cells turned bad and is outputting too much voltage so I took out my old multimeter, but it does does not work either, just random readings, so I cannot even measure the batteries.

Very frustrating experience and I need to use my Ladybug to do some debugging on the computer. I guess I need to power up an HP-16C instead.
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03-26-2021, 06:54 PM
Post: #2
RE: I just fried two HP-41s?
(03-26-2021 06:11 PM)hth Wrote:  Yesterday my 41CL just stopped working while I was using it. So I recharged the battery and let it sit overnight. I tried to insert the battery again and no go.

Today I took a new 41CX and swapped batteries between them. It did not help and the 41CX made a single BEEP at power on and now it is dead too.

Now I wondered if the NiMH cells turned bad and is outputting too much voltage so I took out my old multimeter, but it does does not work either, just random readings, so I cannot even measure the batteries.

Very frustrating experience and I need to use my Ladybug to do some debugging on the computer. I guess I need to power up an HP-16C instead.

Though I use rechargeable batteries in many of my machines, I always keep at least one set of alkaline batteries on hand for each type of machine, just for troubleshooting situations just like this. Do you have any N cells around, maybe even in another 41?

I sure hope it's not what you suggested, and that the 2 machines were not damaged.

Let us know what happened....

--Bob Prosperi
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03-26-2021, 08:20 PM (This post was last modified: 03-26-2021 08:23 PM by BartDB.)
Post: #3
RE: I just fried two HP-41s?
Seems to me like a problem with the batteries. Get some new ones or try some alkaline N cells as Bob suggested (just make sure they're not 12v cells! They will kill your hp-41's).
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03-26-2021, 08:47 PM
Post: #4
RE: I just fried two HP-41s?
Some relief, the mint 41CX came back to life after giving it a rest without batteries. I put in a third set on NiMH and started again.

For the 41CL no luck so far, but I will try it again later with another new set of batteries.
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03-26-2021, 09:06 PM
Post: #5
RE: I just fried two HP-41s?
It's not uncommon for multiple sets of batteries to have a bad cell. Take all the cells out and measure them individually. Throw out any that measure 0V (short circuit) or random readings (open circuit). Anything 0.8V or above is usually salvageable.

Also check your multimeter leads. Put it on low ohm scale and short the tips, you should get a reading of <0.5ohm. Random readings indicate bad leads (has happened often enough with mine that I always have a spare set).
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03-27-2021, 01:42 AM
Post: #6
RE: I just fried two HP-41s?
(03-26-2021 06:11 PM)hth Wrote:  Now I wondered if the NiMH cells turned bad and is outputting too much voltage so I took out my old multimeter, but it does does not work either, just random readings, so I cannot even measure the batteries.

The battery in the multimeter might be low/dead too!

10B, 10BII, 12C, 14B, 15C, 16C, 17B, 18C, 19BII, 20b, 22, 29C, 35, 41CV, 48G, 97
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04-06-2021, 05:24 PM
Post: #7
RE: I just fried two HP-41s?
I can report that both machines are alive again. The 41CL rested without batteries for days, got new ones, flickered up and died back down a couple of times and then decided it wanted to be alive again.

So, both machines are up and running again. The multimeter also have a bad battery.

A third machine (my old well used 41CX halfnut), is however flakey now....

I guess these machines are getting old, like myself, LOL
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