HP-67 Charge Issues

[dcs]

I have an HP-67 question, regarding behavior while connected to charging power.

While on battery - it functions normally.

While on charge power (original HP power supply, rebuilt battery pack), the display flickers and key entry is very erratic (example: keypress of '5' results in '5555' on the display). Unusable.

I seem to recall being able to use it while plugged in (when I first obtained it), but am starting to doubt my memory.

Does this behaviour sound familiar to any experienced HP-67 users?

Thanks in advance for any advice.

[Maximilian Hohmann]

Hello!

(05-21-2022 07:36 PM)dcs Wrote:  Does this behaviour sound familiar to any experienced HP-67 users?

That's a common problem with all kinds of "ancient" electronics: Dried out electrolytic capacitors, especially in the power supply. With a bad capacitor, instead of smooth direct current, the calculator will receive rectified alternating current that oscillates between 0 and 10V (or so) either 50 or 60 times per second depending on where you live.
The capacitors are fairly easy to replace provided you have a soldering iron.

Regards
Max

[GreyUser]

Stop using the charger immediately, it could damage the calculator. The 400uf filter capacitor has failed and is allowing ac ripple on the dc supply. Replace with a 470uf 16 volt device as you’ll never find 400uf and it’s not critical, capacitor tolerances are quite large.

If your charger has a voltage selection switch, be careful upon re-assembly. The switch contacts must be oriented in the same direction to prevent damage, the contacts small pin goes in the hole which is only on one end. It will make sense when you look at the bits when it’s open…

IIRC the charger schematic (in ascii art) is in the archives courtesy of Tony Duell.

Edit: link added. https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=390

[teenix]

(05-23-2022 02:10 AM)GreyUser Wrote:  IIRC the charger schematic (in ascii art) is in the archives courtesy of Tony Duell.

Available in this document also by Tony Duell

http://www.hpcc.org/cdroms/schematics5.0...c/hp67.pdf

cheers

Tony

[dcs]

(05-22-2022 04:31 PM)Maximilian Hohmann Wrote:  The capacitors are fairly easy to replace provided you have a soldering iron.

Thanks Max.

I have soldering iron and basic skills. Will give it a go.

[dcs]

(05-23-2022 02:10 AM)GreyUser Wrote:  Stop using the charger immediately, it could damage the calculator. The 400uf filter capacitor has failed and is allowing ac ripple on the dc supply. Replace with a 470uf 16 volt device as you’ll never find 400uf and it’s not critical, capacitor tolerances are quite large.

If your charger has a voltage selection switch, be careful upon re-assembly. The switch contacts must be oriented in the same direction to prevent damage, the contacts small pin goes in the hole which is only on one end. It will make sense when you look at the bits when it’s open…

IIRC the charger schematic (in ascii art) is in the archives courtesy of Tony Duell.

Edit: link added. https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=390

Thank-you for the advice.

I just got my HP-35 out of storage and that charger works fine on the 67. I'm not sure why I didn't think to try it before now. Just assumed it was something failing with the calculator.

Hopefully I've not damaged it. Have not been using it much lately for work.

The guilty charger does have a voltage selection switch. I will be careful.

It looks like it has been opened in the past. There is some shrink-tube added as strain relief.

[dcs]

(05-23-2022 02:10 AM)GreyUser Wrote:  Edit: link added. https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=390

Both of my chargers are 82002A, one having screen printing details and the other raised lettering in the bakelite.