82002A Question (nothing to do with that auction website)



#10

Hi all,

I have an 82002A AC Adapter that stopped working. I am not an electronics genius, but I was wondering if anyone has an idea how I could fix it?

Thanks!


#11

What do you mean by "stopped working"?

I would guess you mean that it doesn't have any DC output (or whatever output it is supposed to have).

Really stupid question (but it happens all the time): is it plugged in, and is the wall socket really hot (i.e. supplying power)?

Do you have things like a voltmeter handy?

Can you verify that whatever it is powering works when connected to a different power source?


#12

I have two 82002A adapters. When I use one on my 67, the 67 charges up just fine. I use the other 82002A on my 35. (I know this seems redundant). I try charging, and nothing. Then I took my 67 adapter and charged with it, and the 35 took the charge fine.

Bottom line, one of them just isn't doing anything.


#13

One of the three wires in the power cord of the charger that came with my 35 was broken next to the two philips screws that are closer to each other, where they usually break. This can be checked by gently pushing the cord towards the charger whilst moving it and checking if the display lights up at times. Alternatively, the cable can be checked with a meter before trying to find a defective part inside. This shouldn't be difficult as there are only a few components therein.

Gerson.


#14

It is far more common for the wires to fracture at the calculator plug end. The same procedure, pushing the wires in, will most but not all times work for isolating the failure. The plug can be sliced open and things repaired but it is tricky to get a good result the first few times you attempt it.

If the wires are fractured at the wall wort end, it's easy.

The other common failure is the 400uf electrolytic, I replace those in all the 82002's I get, working or not.

See Tony's article for reference: 82002 schematic


#15

Thanks for the tip. I've always taken care not to bend the wires but I'll be even more careful. I should have replaced the 400 uF capacitor as I had to remove it anyway to solder the wires in place. At least the charger can always be opened, unlike these modern devices.

Gerson.


#16

Some are harder than others to open. There are some things I've noticed:

1) Labels that cover the screws at the bottom. I just use a sharp modeling knife to cut the label away following the molded case hole as the guide. I find that works better than trying to lift the label off for access, they bend and get ratty looking. IMO, two small holes exposing the screws are better.

2) Some units use T7 security type Torx screws. These little nasties are almost impossible to get out without the proper bit. They're the Torx configuration with the little pin in the center - which needs the bit with the corresponding hole in the center. Some time ago I bought a 40 piece security bit set to get that one T7... and subsequently found them individually carded for $1.49 each at a local hardware store. Now I have three ;-)

3) Molded case/no screws 82002 variant: Very nasty, almost impossible to open. They are quite different internally, different circuitry. I did bust open a dead one just to see. Those are better left alone when dead, harvest the cord if it is good and pitch the rest.

#17

Thanks Randy, I looked inside at it and saw some burn marks near a resistor. I can get one of my friends to help with soldering maybe... You think it is the 400 uf then?


#18

If the display flashes or otherwise acts weird, it is usually the capacitor. A 470 uf, 25 volt radial lead aluminum electrolytic is a good replacement as 400 uf is not a common value. Tolerances on this type of cap can be as wide as +80/-20% so the value change is not an issue.

The brown area is usually near the 470 ohm resistor* that supplies base current to the pass regulator. They can go high or even open due to the heat. Measure it, replace if necessary.

*=yellow-violet-brown-silver color bands. That's if it isn't toasted.

PS: The easiest way to test a 82002 is with a voltmeter. Assuming a digital type, set the meter to a ~20 volt DC range, you don't want it auto-ranging. Stick the negative lead in the center hole of the charger plug, calculator end. With the lead at the bottom, put the plus lead in the right hole. The DC voltage should be around 4.5-5.0 vdc. If you don't read anything, wiggle the wire at the plug end and see if voltage appears. If the voltage is intermittent, the problem is usually fractured wires right where they enter the strain relief of the plug.

If it's good, move the plus lead to the left hole, it should measure about 16 volts. If good, set the meter to read ~20 volts AC. With the probe still in the left side, check the AC voltage. It should be below 0.2-0.3 volts AC. If it's any higher than that, the 400uf cap is bad.


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