Repairing & restoring HP82002 - advice needed

[albertofenini]

Dear All, we are back, to school, to work and to our lab ...
We would like to bring back to life some of our Classic Chargers,
some of them had the connector broken so the first advice is where we could find a good
replacement for that.
We know that modern USB cables are available to charge the units, but the fun would be less
than putting together these pieces ...
Also, does anyone has found a good replacement for the transformer ?
Looking around for some documentation we have found Jaques Laporte scheme but there is no indication of what the secondary voltage should be, differently from another scheme that
says 8V/5VA
thanks for any help !!!
   
   

[teenix]

You could try just measuring the AC output voltage from the transformer. With nothing connected to the charger it should be close to the no load voltage, or disconnect the transformer output entirely before measuring. From reading around, I thought it may about 16VAC but not sure. The voltage rating of the 400uF capacitor may give a clue.

Be careful poking around mains voltages :-)

cheers

Tony

[albertofenini]

Thank you very much, we'll try it out and keep you posting !!

[Sadsilence]

Hi,

indeed open curcuit voltage of calculator supply path is above 15V.

So far I have never come across a faulty transformer inside Classics chargers. So no transformer advice from my side.

Normally output capacitor is dead. Then output voltage(s) (when a load, e. g. calculator is attached) have a measureable AC portion and Classics calculator display flickers or do not work at all. You can replace it with any modern 470uF/25V oder 470uF/50V capacitor.

When there are AC/DC output voltage(s) of zero normally fuse inside is dead. I vaguely remember that I used a matching (in size and rating) SMD fuse as replacement in such cases.

Best regards,

Werner

[Paul Berger (Canada)]

I have repaired several of these and the majority of them it was due to a broken wire near the calculator end. I find the breaks using the continuity check on a DVM attaching one lead to the end of the wire inside the wall end and the connectint the other lead to a needle which I push through the insulation. I have not found a replacement for the connector at the calculator end and to be honest never really looked. What I did to repair wires broken near the calculator connector is cut the wires before the break, slice open the connector just below the wide top part, but not cut it off completely but leave it as a flap still connected at the end where the wires come in. Next I carve out a cavity inside to dig out the wires and the top of the connector pins. I then work the old wire out of the strain relief, and bring in the end of the good wire strip the wires and solder them to the top of the pins. Once that is done and I verify that all is well, I fill the cavity with epoxy and glue down the flap with contact cement.

If the break is further away or at the wall wart end it is much easier to repair, if I was to repair a break in the middle of the wire I would cut the broken wire at the break and insert a sort piece of wire to join the broken end and cover the spot with heat shrink.

I have only ever had one or two electronic component failures usually bad capacitors, but I have had at least one where the pass transistor in the charge current regulator failed. If the 5V capacitor is bad, you will see flickering in the display when running off of the 5V.

Paul.

[albertofenini]

Thanks for all the replies,
as for the cables, we are in touch with people that produce the USB cable in order to
buy just the prong.
It want be like the original but it is better than nothing and it will do.
However, the ones we are trying to repair have had the transformer broken, at least,
which is why we are looking for a replacement.
Will do more tests over the weekend by opening a working one and we will post here !
Thanks again !!

[vassilisprevelakis]

(09-17-2019 02:47 PM)Paul Berger (Canada) Wrote:  I have repaired several of these and the majority of them it was due to a broken wire near the calculator end. [...]

Hi Paul,

This how I remember a technician at the local HP office in Athens, Greece fixing Classic series chargers in the late 70s.

Due to high import duties, the USD to Drachma exchange rate and the relatively low labour rates in Greece at the time, it was cheaper to repair the connector, than get a new cable or charger.

**vp

http://www.series80.org

[Martin Hepperle]

(09-17-2019 02:47 PM)Paul Berger (Canada) Wrote:  [...]
I fill the cavity with epoxy and glue down the flap with contact cement.
[...]

Paul.

A few months ago I had the same problem and I learned that you can buy black, flexible superglue. This is what I used to close the "flap". In my case the cable was broken but also corroded internally over a length of several centimeters starting at the connector.

Another failure of this charger was a broken transformer wire - the charger must have been dropped and one mounting flange of the white plastic bobbin was broken off, taking one of the wires with it. The flange was only dangling by the remaining wires.
After de-soldering the transformer from the PCB I had to perform some surgery to solder a thin copper wire to the last 3 mm of the winding sticking out ... and was surprised that it worked. Finally I glued the flange with 5-min Epoxy back to the bobbin and soldered the transformer back to the PCB.

Martin.