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HP-42S battery drain
07-09-2020, 01:48 AM (This post was last modified: 07-09-2020 02:43 AM by Marcovecchio.)
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HP-42S battery drain
I bought a second hand, perfectly working HP-42S, but I just noticed it has a huge battery drain problem. I measured 17mA, which will drain new batteries in hours.

I have a disassembled HP-17BII at hand, and I just measured it's current draw: less than 1mA on and idle, and a peak of 2mA when making calculations.

I know this has been discussed many times, and with several HP calculator models (I had an HP-28S that showed the same behavior many years ago), but I would like to insist a little more before giving up. I opened the calculator, removed the PCB from the case and removed every component I could from the PCB: 3 capacitors, the diode, the IR led, and even the SRAM and crystal! When plugging the calculator to a power source, I get the same 17mA. This is with only the processor still soldered to the PCB.

I then washed the pcb with isopropyl alcohol and a soft brush, in an attempt to remove contaminants that might be shorting the delicate processor pins, but it didn't work, still 17mA. I resoldered everything back into place. Calculator works, and still the same 17mA.

May I consider the processor is damaged forever? Is there anything else I can try? Is it possible that it's locked in a "power waste" state that even a reset won't clear? Is there any "stronger" reset than shorting - and + battery pins with no batteries installed?

And a last question: why this happens so much to HP calculator processors? I have read about a lot of cases like this over the years. How can a processor fail to the point it draws hundreds of times the current it used to, but keep working perfectly?

Thanks for your help!

Eduardo
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Messages In This Thread
HP-42S battery drain - Marcovecchio - 07-09-2020 01:48 AM
RE: HP-42S battery drain - jebem - 07-09-2020, 05:38 AM
RE: HP-42S battery drain - Marcovecchio - 07-09-2020, 12:24 PM
RE: HP-42S battery drain - Allen - 07-09-2020, 01:45 PM
RE: HP-42S battery drain - Marcovecchio - 07-09-2020, 06:09 PM
RE: HP-42S battery drain - Marcovecchio - 07-13-2020, 02:55 AM
RE: HP-42S battery drain - Dave Shaffer - 07-14-2020, 04:04 AM
RE: HP-42S battery drain - KF6GPE - 07-14-2020, 05:25 AM
RE: HP-42S battery drain - GreyUser - 07-17-2020, 02:25 AM
RE: HP-42S battery drain - Marcovecchio - 07-18-2020, 04:36 AM
RE: HP-42S battery drain - ijabbott - 07-18-2020, 02:24 PM
RE: HP-42S battery drain - Marcovecchio - 07-18-2020, 08:29 PM
RE: HP-42S battery drain - Marcovecchio - 08-05-2020, 02:56 AM



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