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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 24th Nov 2022, 8:31 pm   #1
newlite4
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Default ICOM IC-M21 Mystery part

Just starting to rebuild the Ni-Cad pack on this one. Under the batteries is this component which is in series with the batteries. Difficult to measure the resistance, it looks as though it has overheated, but it reads around 1Mohm. It is marked 32102 with BBS75B2N-03 on the second line. I wondered if it was some sort of protection device and if it was strictly necessary, there is already a 1NK14 diode between the positive pack terminal and the first battery.
Neil
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Old 24th Nov 2022, 9:21 pm   #2
SiriusHardware
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Default Re: ICOM IC-M21 Mystery part

It's almost certainly a one-shot thermal fuse which, if it is, did exactly what it was designed to do (went open circuit / high resistance when the batteries got too hot).
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Old 25th Nov 2022, 9:23 am   #3
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Default Re: ICOM IC-M21 Mystery part

Thanks for your input. That makes a lot of sense. Possibly blew open as a result of an accidental short circuit of the battery terminals.
Neil
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Old 25th Nov 2022, 9:41 am   #4
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Default Re: ICOM IC-M21 Mystery part

Wouldn't any fuse be downstream of the battery terminals and unaffected by a direct terminal short? (Unless it were of sufficient duration to heat the battery up significantly perhaps?)
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Old 25th Nov 2022, 11:14 am   #5
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Default Re: ICOM IC-M21 Mystery part

If it's a thermal fuse as I think it is then it would go open circuit as a result of the battery temperature going above a certain threshold, howsoever caused.
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