HP80 battery pack voltage reversed

[elgin113]

I had installed a new battery pack for my HP80 with 3 NiMH batteries.
However, when I was copying the old battery pack I accidently reversed the terminals.
When I pluged the charger in it turned on OK and worked but an hour later the screen was blank.
Is the calculator permanently damaged or can it be repaired?
Thanks for your replies.
David

[Jeff O.]

(11-03-2016 11:28 AM)elgin113 Wrote:  When I pluged the charger in it turned on OK and worked but an hour later the screen was blank.
Is the calculator permanently damaged or can it be repaired?

To be clear, you put the pack in the calculator and plugged in the original charger? If so, you probably have done no damage to your calculator, but the charger may have been damaged. Classic chargers have two circuits in them, one regulated to about 4.5 Volts to power the calculator, and another circuit which charges the battery. When you plug the charger into the calculator, it disconnects the battery from the calculator circuitry and provides 4.5 Volts from the charger to the calculator. The battery gets connected to the charging circuit of the charger. So when you turned it on, the charger powered the calculator, but by an hour later, perhaps the load of attempting to charge the reversed batteries had killed the whole charger.

There is probably a schematic available on this forum to help you determine if there is fuse or other repairable component in the charger.

[Harald]

(11-03-2016 11:28 AM)elgin113 Wrote:  I had installed a new battery pack for my HP80 with 3 NiMH batteries.
However, when I was copying the old battery pack I accidently reversed the terminals.
When I pluged the charger in it turned on OK and worked but an hour later the screen was blank.
Is the calculator permanently damaged or can it be repaired?
Thanks for your replies.
David

I would have thought you probably killed the charger. The calculator itself might have survived. You could try using 3 AA alkaline batteries to test the calculator.

If it hasn't survived, I can refere you to my post in the classified section...

[elgin113]

Thanks very much for the replies.
I reversed the battery pack now so the positive is on the bottom tang of the connector in the calculator. The pack has just below 4 volts dc and just plugged the battery in and didn't power on. I also tried 3 aa batteries and still no power.
I then read a HP calculator repair site and it said don't reversed the battery pack but didn't say if it damages the batteries or the charger.
I checked the charger voltage and one side says about 4.5volts and the other about 16 volts.

Not sure what do next?

[Jeff O.]

(11-03-2016 01:31 PM)elgin113 Wrote:  Thanks very much for the replies.
I reversed the battery pack now so the positive is on the bottom tang of the connector in the calculator. The pack has just below 4 volts dc and just plugged the battery in and didn't power on. I also tried 3 aa batteries and still no power.
I then read a HP calculator repair site and it said don't reversed the battery pack but didn't say if it damages the batteries or the charger.
I checked the charger voltage and one side says about 4.5volts and the other about 16 volts.

Not sure what do next?

Those sound like normal charger voltages. Did you ever turn the calculator on with just the reversed battery pack installed?

Also, just to cover the basics, did the calculator ever work while in your possession? Off of another battery? Off of the charger with no battery installed? (No harm will come to the calculator operated off the charger with no battery installed.) Did you try jiggling the on/off switch?

[PANAMATIK]

(11-03-2016 01:31 PM)elgin113 Wrote:  ... The pack has just below 4 volts dc and just plugged the battery in and didn't power on. I also tried 3 aa batteries and still no power.

Be sure, that the two outer pins of the charge connector are connected by the small metal piece inside, when the charger is not plugged in. If they are connected and the calculator doesn't power up with the batteries, then the internal power supply of the calculator has got damage.

See HP calculator power supplies for more information. HP-80 schematic should be similar to HP-35.

The measured 16V at the charger are normal, because it is a constant current source and the voltage will go down, when charge current flows. The 4.5 V is the constant voltage for the calculator during charging.

If only the power supply is damaged then the transistors and diodes can be repaired, because replacement components are available today like 2N3904 for Q2 or BC337.

Bernhard

[elgin113]

(11-03-2016 04:41 PM)Jeff O. Wrote:  

(11-03-2016 01:31 PM)elgin113 Wrote:  Thanks very much for the replies.
I reversed the battery pack now so the positive is on the bottom tang of the connector in the calculator. The pack has just below 4 volts dc and just plugged the battery in and didn't power on. I also tried 3 aa batteries and still no power.
I then read a HP calculator repair site and it said don't reversed the battery pack but didn't say if it damages the batteries or the charger.
I checked the charger voltage and one side says about 4.5volts and the other about 16 volts.

Not sure what do next?

Those sound like normal charger voltages. Did you ever turn the calculator on with just the reversed battery pack installed?

Also, just to cover the basics, did the calculator ever work while in your possession? Off of another battery? Off of the charger with no battery installed? (No harm will come to the calculator operated off the charger with no battery installed.) Did you try jiggling the on/off switch?

The calculator did work with the old dead batteries running off the charger.
I turned the calculator on when charging with the new reversed batteries and worked but stopped working after an hour or so.Then I tried the reversed batteries only after that thinking it was the charger and didn't turn on.
Never tried it without batteries on the charger or off other batteries.Switch works fine.

[Alejandro Paz(Germany)]

Quote:Never tried it without batteries on the charger

That is one of the models that gets fried with the charger only (withOUT the batteries).

Quote:Then I tried the reversed batteries only after that thinking it was the charger and didn't turn on.

You may have damaged the calculator .

[Harald]

If you are lucky it is only the PSU on the calculator PCB. As PANAMATIK said you could check the diodes and transistors. But it is possible more than that is damaged.

Is the calculator of sentimental value to you? If repairing diodes and/or transistors does not help, you could try replacing the main PCB and see if that helps. I might have a replacement PCB for you soon, but I am still waiting for the mail to turn up
You can also use a main PCB of an HP35, 45, (or 70) to check if the display drivers are still ok.

[PANAMATIK]

(11-04-2016 08:28 AM)Alejandro Paz(Germany) Wrote:  That is one of the models that gets fried with the charger only (withOUT the batteries).

I don't think so. All Classic models HP-35/45/55/65/70/80 can be run without batteries, because they have a fixed 4.5 V power from the charger and don't need the batteries as buffer.

Bernhard

[Alejandro Paz(Germany)]

Quote:I don't think so. All Classic models HP-35/45/55/65/70/80 can be run without batteries, because they have a fixed 4.5 V power from the charger and don't need the batteries as buffer.

Bernhard

, Sorry. The ones that could be destroyed are the HP-21, 25 and so on.

[Harald]

(11-04-2016 11:27 AM)Alejandro Paz(Germany) Wrote:  

Quote:I don't think so. All Classic models HP-35/45/55/65/70/80 can be run without batteries, because they have a fixed 4.5 V power from the charger and don't need the batteries as buffer.

Bernhard

, Sorry. The ones that could be destroyed are the HP-21, 25 and so on.

65 and 67 shouldn't be used without a battery installed either. The card reader draws its power directly from the battery and could be damaged as well.

[Jeff O.]

(11-03-2016 04:43 PM)PANAMATIK Wrote:  Be sure, that the two outer pins of the charge connector are connected by the small metal piece inside, when the charger is not plugged in.
Bernhard

Double check this. If the calculator has ever been opened, that piece may have fallen out. The calculator will still work when powered by the charger without this piece. If missing, a replacement can be harvested from a donor, or a new one fabricated from brass sheet.