Repairing a 82022B charger (with P.S. to Geoff Quickfall)

[Karl-Ludwig Butte]

Dear all,

one of my 82022B chargers broke some days ago. A first investigation showed that the fuse was melted. But after replacing it, the same thing happened again immedeately. A further search for the root cause showed that transistor Q3 shortcircuited. It's a NPN power type with a "M726" printed on it. Alas I couldn't find any datasheet at the Internet. Does anyone know with which transistor available today I can replace it ?

Any hint will be very much appreciated - thank you very much in advance.

Kind regards

Karl

P.S.: By the way, Geoff, if you're reading this, may I ask how about your book ? Will it be ready for ordering soon ?

[Ignazio Cara (Italy)]

Hello Karl,
take a look at this fantastic job of Jacques Laporte about the HP-35 and more old HP calculators:

http://www.jacques-laporte.org/HP35%20power%20unit.htm

Take care and regards.

Ignazio

[Karl-Ludwig Butte]

Hello Ignazio,

thanks a lot for your answer - I'll try my luck.

Best wishes and kind regards

Karl

[Karl-Ludwig Butte]

Dear All,

thanks again for the link Ignazio and thanks Jacques for the excellent technical content.

I succeded to repair the charger by replacing the defective Q3 with a BD128 which should be available at any electronic shop. A bit more difficult was to find a supplier for the fuse, a so called pico-fuse, which also was defect. For people living in Germany I found it at Reichelt Elektronik.

Best wishes and kind regards

Karl