Repairing a 67 charger ?



#12

Hello,

I have tried to find some info about testing/repairing a HP67 power charger: no success.

Mine seems to deliver nothing before I unsoldered the regulator: now it outputs 15V... But it doesn't seems to charge the battery anymore.

I have 2 questions:

-what did I do wrong?

-can I solder another regulator bought in a regular shop?

Can anybody help?

Thanks,
Olivier


#13

Quote:
I have tried to find some info about testing/repairing a HP67 power charger: no success.

You didn't try very hard: Classic charger schematic Thanks to Tony Duell!

The most common classic charger failure is fractured wire(s) at the calculator plug end or where the wire exits the charger body. The charger end is easy to repair, the plug, while it can be done very neatly, usually ends up a disaster on the first attempt. Use of sharp objects required...

Common component failures are the 400 uf capacitior followed by the pnp pass regulator for the charger side. All parts in a classic charger are common 1970's electronics, nothing is HP specific.


Edited: 9 Nov 2006, 9:40 a.m.


#14

Sorry Randy,

I must have been lazy... Since I'm not an electronics guru, I was afraid to make a mistake. I have dismounted the power supply but prior to change all possible components, just to be sure they're new, I prefered asking.

Do you suggest that the plug that goes in the calculator may be broken inside (not visible, so)?

Also, will a common 5V regulator from the shop do the job?


#15

Randy described the most common problems, they may not be related to your problem.
The 15V you measure are OK (this is the charging current without load)
Make sure the connections in the calculator are ok, that the battery is working, and that there is no corrosion on the contacts


#16

Quote:
Make sure the connections in the calculator are ok, that the battery is working, and that there is no corrosion on the contacts

About connections in the calculator itself, I ain't been courageous enough to dismount it yet... The cord itself seems to be OK from end to end. Contacts are good and the battery is a brand new one bought from a specialist(?) on eBay.

I'll try to check further and check individul components inside the pwoer supply.

Again:

will a common 5V regulator from the shop do the job? The original one seems to block charge.


#17

Quote:
Again:
will a common 5V regulator from the shop do the job? The original one seems to block charge.

A 5 Volt regulator does not seem to be applicable. The 67 charger supplies two separate outputs: one a regulated 4.2 Volt source that powers the calculator, and the other a 55 mA constant current/variable voltage source that charges the battery pack.
Quote:
Do you suggest that the plug that goes in the calculator may be broken inside (not visible, so)?

It is a very common problem for the wires to break inside the insulation at or near the junction with the plug.
Quote:
The cord itself seems to be OK from end to end.

In what way does it “seem” to be OK? Verify continuity from the contacts in the plug to the places where the wires are soldered inside the charger housing, to insure that the above problem has not occurred.

#18

Quote:

In what way does it “seem” to be OK? Verify continuity from the contacts in the plug to the places where the wires are soldered inside the charger housing, to insure that the above problem has not occurred.


That's what I did and the Ohmmeter says OK, from the soldered cable on the PCB to the plug.
#19

I have a question regarding the Classic Charger schematic referred to above that was prepared by Tony Duell. In the constant current charger circuit, there is what appears to be a resistor from the base of the PNP power transistor to ground, labelled "4k7". Other resistors are labelled "13R" and "470R", which I presume mean 13 ohm resistor and 470 ohm resistor, respectively. So what does "4k7" mean? Is this a typo that should have read 47k? Or is it a 4k ohm resistor and the 7 should have been an R? Or?

Edited: 9 Nov 2006, 1:35 p.m.


#20

No, 4k7 is a very common convention in Europe to mean 4.7k (the 'k' is less easilly missed than the '.')

Similarly, a capacitor labelled 6n8 would be 6.8nF (6800pF), one labelled 2u2 would be 2.2 microfarads (the 'mu' is not avaiable in standard ASCII), a resistor labelled 8M2 would be 8.2M Ohms, and so on.


#21

Thanks for the clarification. I tried to figure out what "4k7" might mean, but the best I could come up with was 47k. I would never have thought of the convention you described, which seems quite sensible. However, I think I'll go ahead and change the copy of the diagram that I saved, because I'll likely have forgetten if I ever refer to it in the future.

Edited: 9 Nov 2006, 10:20 p.m.

#22

yikes!...trapped again by Hick's paradoxon of "no more text here"


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