HP80 doesn't work without the battery charger



#23

Hello!
I got a HP80 which is cosmetically very pretty, but doesn't work if the battery charger is unplugged. The batteries are new and tested. I've opened the calculator and found a little corrosion on the batteries' compartment terminals, expecially on the - connector.
I've checked inside to see if the connection were damaged or not by this corrosion, but it seems that everything should be ok. I checked the continuity of the power supply circuit with a tester (I mean the cable connections and I can say that the calculator doesn't work even if I shorcut the two connectors on the plug (I read the article on the main board of the Hp museum )
.......... the spring is clean and quite free of corrosion, so that I don't understand what is going on: the pcb is free from corrosion (I've removed with a vinegar washing the little green dirty I've found) So that I ask you please for any advice which can help me to find the reason of this fault. Thanks


Edited: 31 Oct 2011, 11:53 a.m. after one or more responses were posted


#24

Check that you measure battery voltage at the ac adapter receptacle contact pins on the calculator. Even with the calculator switch in the OFF position, you should measure battery voltage at either of the positive (+) outer pins with the negative voltmeter probe on the center negative (-) pin. If not, you have an open circuit somewhere inside the calculator. It could be a broken wire solder connection, a broken circuit board trace or broken wire. Also, you may have poor contact between the battery and the spring contacts.

Edited: 30 Oct 2011, 10:05 a.m.


#25

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#26

IDK. The OP says he already tried shorting the two outer pins w/o success.

#27

Quote:
Check that you measure battery voltage at the ac adapter receptacle contact pins on the calculator. Even with the calculator switch in the OFF position, you should measure battery voltage at either of the positive (+) outer pins with the negative voltmeter probe on the center negative (-) pin. If not, you have an open circuit somewhere inside the calculator. It could be a broken wire solder connection, a broken circuit board trace or broken wire. Also, you may have poor contact between the battery and the spring contacts.


Thank-you Michael, I'm measuring 3,11 V only between the (-) and the lef pin I don't measure anything between the central pin and the third pin on the right!


#28

Well, in that case I agree with aj that you are not getting a good connection between the spring contact and the pins. Try shorting the 2 outer pins. Also, if the battery voltage is only 3.11 vdc, it is discharged and will not power the calculator.


#29

Michael excuse me but I don't understand, I must measure voltage on both the outer pins, toward the inner pin or just on the (+) one?
Notice that when I test the voltage of course I do it without the cover (it means without the spring)

well, only 3,11V but the battery is the same I use now with a 67 calculator and even the card reader works!!


#30

The bridge contact must be installed and making contact with the 2 outer (+) pins with the ac adapter not connected. The two outer pins are positive (+) and the center pin is common negative (-). If the bridge contact is working properly, the two outer pins will be common positive (+). Place the voltmeter negative probe on the center pin and the positive probe on either outer pins. If your battery is measuring only 3.11 vdc, then I don't understand how it can power the calculator.


Edited: 1 Nov 2011, 10:47 p.m. after one or more responses were posted


#31

with the bridge contact installed and making contact with the 2 outer (+) pins with the ac adapter not connected, the voltmeter negative probe on the center pin and the positive probe on either outer pins I got a value near to 2.50 vdc, but when measuring the battery directly I have 3.49 vdc! I drop that battery inside my hp 67 calculator and it can power the calculator. I have not another teste to check if my meter is calibrated or not.
Anyhow, if I measure these values it means that there's a drop of 1 vdc in the circuit, is that right?

Edited: 30 Oct 2011, 12:09 p.m.


#32

If the calculator is OFF, then there should be no voltage drop. Something may be wrong with your voltmeter or its leads.

Edited: 30 Oct 2011, 12:26 p.m.


#33

Michael, if there is a problem with the meter (we assume it as uncalibrated) we can trust, I suppose, in the relative measures.
There'a fact: with the calculator turned off the voltage is 2.50 vdc, with the calculator turned on the voltage is 0.17 vdc. The voltage of the battery out of the calculator , retested now, is 3.97 vdc.
What do you think about?


Edited: 30 Oct 2011, 12:46 p.m.


#34

It almost sounds like you have an internal short somewhere inside the calculator. You should only see about a 0.2 vdc voltage drop between the calculator in the OFF and ON states. For example, I just checked an HP 55, and the voltages at the pins are OFF = 3.94 vdc and ON = 3.75 vdc.


#35

Do you have a schematic of this calculator, and test points just to try to find this shortcut?

#36

Quote:
I have not another teste to check if my meter is calibrated or not.

You can check your meter with a good battery or two (or three or ...).

Do you have a fresh, unused AA, C, or D alkaline battery available? They should give you almost 1.60 V. I measure around 1.56 - 1.59 V on brand new batteries. You can put 2 or more in series to check your meter at higher voltages.

A fresh-from-the-charger NiMH AA should give you between 1.30 and 1.35 V.


#37

Quote:

You can check your meter with a good battery or two (or three or ...).

Do you have a fresh, unused AA, C, or D alkaline battery available? They should give you almost 1.60 V. I measure around 1.56 - 1.59 V on brand new batteries. You can put 2 or more in series to check your meter at higher voltages.

A fresh-from-the-charger NiMH AA should give you between 1.30 and 1.35 V.


Thank-you Dave, I charghed a NiMH AA and got 1.34 V.
It means maybe I can trust in my meter..........

Edited: 31 Oct 2011, 7:19 a.m.


#38

Quote:
with the bridge contact installed and making contact with the 2 outer (+) pins with the ac adapter not connected,

Are you VERY SURE that the bridge spring IS making contact? Did you check for continuity between the two outer pins?

I had a similar problem in the past with an HP-67 that after some days of search finally found that the culprit was a bridge spring that "seemed" to be making contact but in fact was not.


#39

Quote:

Are you VERY SURE that the bridge spring IS making contact? Did you check for continuity between the two outer pins?

I had a similar problem in the past with an HP-67 that after some days of search finally found that the culprit was a bridge spring that "seemed" to be making contact but in fact was not.


I tested the continuity at first between the two outer pins, when I read this advice on the forum here, I tested it elecctrically with a digital multimeter, then with a analogic one that I found out last sunday, so that I'm pretty sure that there's continuty
What do you mean, please, with "that "seemed" to be making contact but in fact was not" ?

Edited: 2 Nov 2011, 1:56 a.m.


#40

Have you checked the wires from the battery spring contacts to the plug pins with your ohmmeter? It's not unhead-of for battery electrolyte (from a leaking battery pack) to creep inside the insulation and corrode the wire itself.


#41

Hello Tony, thank for your interest! I checked the continuity at first with the digital multimeter (buzzer) and even if I test it now, I get sound, but actually, when I test it with the analogic ohmeter, the result is quite different: the continuty is not "continuous" (excuse me the words) between the spring on the negative pin (the central one). I think that the problem should be not due to the wire but to the corrosion on the surface of the spring; infact if I test it between the pin and the lower part of the spring (the one which goes into the chassy) there are no problems, but if I move the probe along the upper surface of the spring, the resistance change and somewhere there is no contact!. At the end (the top) of the spring, the contact is good, but I don't know what happens when I pus the battery into my calculator and lies in the compartment..I mean if the contact between the pack and the spring is good or not. I can imagine that at least the upper part should get in contact, but in that case, the calculator should be powered, what do you think about? I've tried at the beginnig to apply a drop of soldering wire, on the corroded spring, but I was not able to pristine the surface (the corrosion doesn't allow the the soldering wire to attach-on). Maybe it need to be cleaned or prepared somehow. I confess to have not geat experience in soldering.........

EDIT: just edit now, I placed a piece of metal on the spring, then I drop the battery pack, I got this way a better contact and the calculator works!! It means that the problem is on the spring, I must get a better contact, what can I do?


Edited: 2 Nov 2011, 11:33 a.m.


#42

Remove the spring and re-tension it by bending it back, then replace it. There's also likely a thick oxide coating on the contacts. Use some DeoxIT on them, it works wonders.

Edited: 2 Nov 2011, 11:46 a.m.


#43

Thank-you Katie, thank-you all, my friends, thank you for your help!
HURRA!!! The machine now works and let's go now to test whole its functionality....
The spring was bent just to get more strenght, scraping it with a good knife I removed the "dust" and now it looks working great! without any charger.........THANK YOU AGAIN


#44

I'm glad you got it working!


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