Repair of an HP82004A Power Reserve Pack

[albertofenini]

Hello everyone, first of all we hope that everyone is doing fine during these hard times !
Best wishes for everyone and good luck to all of us !!

Yesterday we tried to fix an HP82004A, a Power Reserve Pack for the Classic serie.

We use these to keep a Classic Battery Pack always ready, and while we normally
connect it to a Classic Power Supply, this one was connected with a USB cable to
a Kindle USB power supply.

Worked fine for a while unless the led that usually turns on when a battery pack is in place went off.

Yesterday we replaced the led and to our surprise it didn't fix the situation, as a
matter of fact the original led was working.

We replaced then the transistor with a spare unit like the original, and what's happening now is
that the led stays on even when a battery pack is not in place, just because a Power Supply is connected to the Reserve Pack.

We checked the voltage and the current using another working Power Reserve Pack
(which behave normally) and both provide a 15 volts at the terminals and if a battery is in place both provide a 55 mA current.

That makes us think that the repaired unit is working, but then why the led is always on when
the Power Supply is connected ?

Thanks for any idea you want to share !!

Stay safe everyone

Pictures here : Repair of an HP82004A Power Pack