HP-65 repair



#12

I've just acquired a 65 that has had a pretty bad battery leak.

Before I took it appart, I cleaned the battery cavity and contacts and tried it. Nothing. Then I plugged in a charger and viola it can to life.

Well almost. It briefly showed 0.00 (left justified) but now most of the time shows 00 00 (center/right). Does the display show four 0's in program mode?

More importantly, NO KEYBOARD ACTION.

I decided the leak must have been bad enough to foul something inside. Now I have it apart and the card reader PCB had some copper oxide buildup as did the backside of the keyboard. There is some oxide on the front side and I'm afraid there may be some beneath one or two rows of the keyboard.

I've carefully scraped and washed these areas I can get to. Still nothing when I tried it. Works the same way.

suggestions? keep cleaning or is it on of the chips?

Peace


#13

Do you have any electrical contact cleaner? It might be worth giving the contacts a good douse-and-scrub. I found a can at Radio Shack a while back for the princely sum of $10.

Failing that, any corrosion on specific components that might help localize failure?


#14

I'd be wary of Radio Shack contact cleaner on calculators. Much of the contact cleaner I've seen there contains oil (Look at the ingredients on the can, see if it says "Mineral Oil" somewhere). Problem is, lots of contact cleaners were formulated for old open-air variable capacitor TV and radio tuners, not so much for digital electronics. The contact cleaner I've had the best results with is Deoxit.


#15

Good point. I checked my bottle and it does not list mineral oil as part of the formulation. That said, when I do use the cleaner, I try to confine it to the metal parts only, sometimes by spraying it onto a Q-tip and using the saturated cotton swab to clean metallic parts.

-Tim


#16

I'll try it. You mean the gold plated contacts connecting the boards, correct?


#17

I'd probably go for those, as well as the keyboard switch contacts and anything near the area where the leak occurred.


#18

Well I've tried some Newtek "Tronic Clean" It was the only thing I could get locally. I'll try to get Deoxit later.

Cleaned up the gold pretty good. While moving items around the ground wire broke off of the keyboard. Perhaps it was this bad connection causing the issue.

In any event, it's ALIVE.

Anyone have some pointers why the unit will not run without the charger? I repaired a 35 by fixing the gold contact in the socket. I tried this here, but didn't seem to fix. This one is far less corroded than the 35.


#19

Quote:
Anyone have some pointers why the unit will not run without the charger?

Could be the bridge contact in the AC adapter receptacle isn't making good contact. Try shorting the 2 outer pins. Otherwise, there is probably an open circuit someplace between the battery terminals and the circuit board.

Also, don't operate the calculator from the AC adapter w/o a battery installed; you may damage the card reader electronics.


#20

I've had the battery in everytime I plug it in.

I haven't tried the card reader yet, hopefully it is ok


#21

I can't find a break.

Continuity from the contact to the socket pin (red wire). the contact is pretty coroded where the wire connects but is hangin on.(anyone know a source? I presume a donor calc is needed)

Continuity from pin (either one) to the pad for the power switch.

Still nothing. When unit is plugged in, everything works. If the battery loses contact the UNIT SHUTS OFF. Is this a clue?


#22

The calculator does not need a battery to operate from the AC adapter, so loss of battery contact should not cause the calculator to turn off. When you insert the AC adapter plug into the calculator, you bypass the battery for power to the calculator main board, keyboard and LED display. Only the card reader receives power from both the AC adapter and the battery, which is why the card reader circuit can be damaged if a battery is not present, since it's receiving power from the charging side of the AC adapter, which outputs about 17 vdc no load.


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