82002A Charger Repair question...

[BarryT]

Hi all,
. After recently acquiring a 55 and a 67, I ended up with 3 chargers. Fortunately 1 of them works, so I actually get to play with my wonderful new toys
I have a question regarding one of the non-working ones though.

. I measured the output on each of them, and the one that actually works is putting out 16.35V on the charger portion, and 5.25V on the operational side. One of the others is putting out almost nothing across the board, like 0.03V on each side, so I definitely need to repair that one. However, the other one is pumping out 17.75V on the charging side, but only 4.5V on the operational side.

. My 'assumption' is that upon powering the calculator on, the load pulls things down below what the calculator needs to actually operate; whereas with my other one, the supply is adequate enough that it doesn't drop below any operational threshold. Does that sound about right? I'm pretty sure the charging side is just fine, so I'm not concerned about that.

. If that all sounds correct, what's typically the culprit that would be causing the low operating voltage?

Thanks everyone!

[Sadsilence]

Your assumptions are correct. There is a fabulous site showing curcuits of most vintage HP chargers.

Weak points of classics series chargers are 400uF capacitor, which drains out over years and is not able to stabilize AC/DC conversion any more and a fuse. In first case you get "unusual" output voltages with a high AC ripple. Any 470 uF/35V modern electrolytic capacitor can be used as replacement. In latter case you do get (nearly) zero output voltage(s). There are some SMD fuses around, matching footprint, as replacement.

Needless to say, that you are dealing with high (ac) voltage devices.

[BarryT]

Perfecto... thanks for the reply and information, as well as the link.

I'm hoping I can repair them soon.

-=Barry

[Paul Berger (Canada)]

I have seen more of these fail due to broken wires, and they seem to break at the calculator end, I have repaired a few that where in this state.