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HP Forums / HP Calculators (and very old HP Computers) / General Forum v / HP 21 not powering on - repair/troubleshooting advice

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HP 21 not powering on - repair/troubleshooting advice
01-26-2021, 10:13 PM
Post: #1
dmh Offline
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HP 21 not powering on - repair/troubleshooting advice
Hi,

I received a collection of HP calculators recently including 3 x HP 21, none of which power up at all.

I received some HP 25 in the same lot which all work.

I have used a known working converted battery pack and also tried the warm up suggestion which I found in these forums but still nothing. I'm looking for suggestions of how to test/troubleshoot from here with the thought that maybe I can combine working components from each into a complete working unit.

Was the 21 much different to other woodstock models making it generally less reliable / more likely to breakdown as I find it hard to believe that they are all the same (ie completely dead)?

BTW, I'm a software engineer and not a hardware engineer but am thinking it's worth a shot as I have 3 of them and can learn as I go. I'm planning to get a multimeter so I can do some testing at various points as advised here.

TIA, dmh
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HP 21 not powering on - repair/troubleshooting advice - dmh - 01-26-2021 10:13 PM



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