Battery contacts on Classics

[bshoring]

I've got a classic series calculator that is in otherwise great shape. Cosmetically it looks great and all the functions work just fine with the wall charger. However, the contacts, see photo, don't make contact with the battery pack. I've got 2 new battery packs that work just fine with another classic, but they don't work with this one. I've also tried attaching a 4.5v DC power source directly to these contacts and the calculator fails to start.

Anything I can do?

Thanks.

[teenix]

(04-08-2017 02:17 AM)bshoring Wrote:  I've got a classic series calculator that is in otherwise great shape. Cosmetically it looks great and all the functions work just fine with the wall charger. However, the contacts, see photo, don't make contact with the battery pack. I've got 2 new battery packs that work just fine with another classic, but they don't work with this one. I've also tried attaching a 4.5v DC power source directly to these contacts and the calculator fails to start.

Anything I can do?

Thanks.

They look clean enough, so maybe they have, or something else has broken away inside.

From memory there are 6 screws to undo, 2 you can see, 2 under the rear label and 2 under the lower rubber feet.

cheers

Tony

[olr]

When the machine is powered by battery, the left and right pin for the wall plug (the two lower ones in your picture) must be shorted. Maybe the responsible "spring" fails to make contact.

[AndiGer]

Or you just didn't remove the plug of the charger?!

[rprosperi]

(04-08-2017 04:05 AM)olr Wrote:  When the machine is powered by battery, the left and right pin for the wall plug (the two lower ones in your picture) must be shorted. Maybe the responsible "spring" fails to make contact.

Agree, this is often the problem. Once you are sure the left and right pins in the charger socket both make contact with the metal plate, try cleaning the area where the pins contact the plate with DeOxit (or a similar) contact cleaner.

Edit: Looking again at your photo, there is indeed evidence of oxidation (greenish spots) on the metal plate that connects the left and right pins when the adapter is not installed, so this likely is the issue.

If this does not work, I'd say Tony is right there must be damage inside, which is odd as those battery contacts look as clean as new. While the contact cleaner is handy, also clean the battery contacts (both the contacts in the machine and also on the battery), oxidation is still possible even though they photograph well.

[AndiGer]

Easy to check through-contact with a DMM:
Middle contact of charger to upper battery contact, both others to lower battery contact should go thru with 0 Ohms

[bshoring]

(04-08-2017 02:49 PM)rprosperi Wrote:  

(04-08-2017 04:05 AM)olr Wrote:  When the machine is powered by battery, the left and right pin for the wall plug (the two lower ones in your picture) must be shorted. Maybe the responsible "spring" fails to make contact.

Agree, this is often the problem. Once you are sure the left and right pins in the charger socket both make contact with the metal plate, try cleaning the area where the pins contact the plate with DeOxit (or a similar) contact cleaner.

Edit: Looking again at your photo, there is indeed evidence of oxidation (greenish spots) on the metal plate that connects the left and right pins when the adapter is not installed, so this likely is the issue.

If this does not work, I'd say Tony is right there must be damage inside, which is odd as those battery contacts look as clean as new. While the contact cleaner is handy, also clean the battery contacts (both the contacts in the machine and also on the battery), oxidation is still possible even though they photograph well.

Thanks, OLR and Bob! You hit the nail on the head. Oxidation and/or dirt kept the springs from the metal plate from making contact with the pins. First time I applied DeOxit nothing changed. Then I applied again and used a small piece of cardboard and moved it around between the springs and the pins. Then when I inserted the battery pack, it worked ! I attach a photo of what it is supposed to look like, in case someone else encounters this problem.

I'm a happy camper now. Thrilled that I don't have to open up my near perfect HP-80. BTW the seller apparently was not into electronics and shipped the calculator with the adapter cord still plugged into the unit. I have a feeling it's been stored that way for years if not decades. The seller sold it "as is" as he/she was not even sure if it was fully functional. But I've run through the manual and everything computes perfectly.

It is so great to have this wonderful forum as a resource!

[bshoring]

An update ....

After writing my previous reply, the calculator worked only briefly from the batteries, less than a day.

However, I did find a workaround. I placed a small piece of tinfoil between the plate and the two pins, and cutout a small piece in the middle so there is no way the foil could make contact with the 3rd pin and cause a short. Then I anchored the rest of the tinfoil in the battery compartment so it stays in place. It works fine with this workaround. It also works fine with the adapter and recharges the batteries just fine. I'll still try to get the pins to make contact the normal way. Did try scraping both pins and the plate with emery boards, to no avail. When I look at the pins and the plate and springs with a magnifying glass, it appears they make contact, so something is preventing contact. Perhaps a different version of DeOxit will work. I'll try ordering the gold version and see if that works. In the meantime, I do have a usable HP-80 that is in near-mint condition. Thanks again for your suggestions. They have helped me find a workaround.