Testing HP 82002A Charger

[AndrewL]

Hello!

I recently came across several of these chargers. I have no experience with HP calculators or testing electronic devices. I purchased a cheap multimeter and with a little research I believe I tested this charger correctly but I want to double check with the experts here.

A few of the chargers do not give me any readings. However 3 of them all give me the same reading.

I inserted the probe into the + hole and I get a 36 (volt?) reading using the middle hole as a ground. When I test the - hole I get 10. Is this correct? I have a new in the box charger that gives me this same reading as the used one.

I am a reseller and I want to go the extra mile to make sure I have a happy customer.

Thank you all very much. These old calculators are very cool!

[Paul Berger (Canada)]

From + to - you should get 15 to 17V on an unloaded charger between - and the unmarked hole it should be 5V. 36V is too high is the 110/220 switch set correctly? If there is no output it may be that there is a broken wire in the cord. Between the two outer pins I get about 11V.

[AndrewL]

When I test it in that order I get 24 from + to - and 10 from - and middle hole. The switch on the back is on the lowest setting. Any idea why the voltage would be this high? Getting the same reading on multiple chargers.

[Dieter]

(04-30-2016 02:41 AM)AndrewL Wrote:  The switch on the back is on the lowest setting.

What is "the lowest setting"? The switch selects between 110 and 220 V input voltage. What's the mains voltage in your region?

And what kind of multimeter do you use? What is the exact setting? Make sure the device is set up for measuring DC voltages.

Dieter

[Paul Berger (Canada)]

(04-30-2016 02:41 AM)AndrewL Wrote:  When I test it in that order I get 24 from + to - and 10 from - and middle hole. The switch on the back is on the lowest setting. Any idea why the voltage would be this high? Getting the same reading on multiple chargers.

Well the middle hole is actually the - connection, looking at the holes with the middle pin at the bottom left = +, middle = -, and right=+5V.

The voltage across + and - is just the rectified and filtered output from the transformer so it will vary a little with the line voltage. I hooked one of mine up to a variac and with 105VAC input the output was 14.4V at 120VAC it was 16.56V so it does not vary a lot. In your first post you said you measured 36V between + and the middle pin which is double what I measured with 110VAC input, so either you line voltage is around 220VAC or as previously suggested you do not have your meter set correctly.

The 5V output is regulated so should be very close to 5V, you reading of 10V between what I suspect is supposed to be the 5V hole and the middle would suggest the regulator has failed, possibly due to high input voltage.

They are fixable, the regulator is a simple design using discrete transistors and a zener diode, I suppose one could even replace it with a modern 3 terminal regulator. The power cube itself is held together with screws so can be taken apart easily, however when open and plugged in AC line voltage may be exposed inside so care is needed. Breaks in the wires are more difficult as they normally occur near the connector or the body of the adapter. I locate the breaks using the continuity check function on one of my meters. Sometimes the breaks may be intermittent so flex the wire a bit the see if it breaks, this is usually easier to detect if you have an audible continuity checker. To find the location of a break leave one lead connected to the end of the wire and connect the other to a small pin or needle and push it through the insulation along the wire to determine where the break is. Flexing the wire will often give you a general idea where the break is as well.

You should get some voltage between and pair of wires out of the three if you do not get that on one of them it probably indicates the wire is broken.

No output could be a failed component like a capacitor, the transformer are designed to put out very little current so if something shorts inside like, a filter capacitor, you will get no output. A bad contact one the input voltage range switch could do that (toggling it back and forth a few time will usually clear that), or an open winding in the transformer.

Paul.

[AndrewL]

I had my multimeter set to AC. I was under the impression AC is for electronics that are plugged into an outlet and DC was for batteries. Once I switch it to DC I get all the correct readings.

Thanks everyone for all the information.