A strange behaviour when my classic calculator is connected to a wall adapter

[aurelio]

(04-22-2020 05:24 PM)teenix Wrote:  

(04-22-2020 02:25 PM)aurelio Wrote:  the voltage is 0,3V on both the sides, when plugged into the calculator
I've retouched all the soldering points, they seems good
the voltage now on the "outside pins" is 5,2 V (supply for the calculator's logic chips), but still not enough

I don't have one of these chargers, so I can't give a comparison.

When plugged into the calculator....

The voltage for the logic side of the regulator should be around 4 volts. This mimics the battery supply.

What voltage do you get across the electrolytic capacitor? I would imagine about 6-8 volts.
If you can check the zener diode it should have about 4.7 volts across it.
The resistor should measure about 470 ohm.
The transistor might have failed also.

Edit: Just thinking, if the voltage is a bit low, it might be worth checking the diodes to see if any have failed. You might be getting half wave instead of full wave rectification.

cheers

Tony

Thank-you Tony I'll check asap,, but if the last voltage test yesterday gave me (un plugged) 5,2V for one side and 16,3 on the other, today the situation is worst, 0,3V a 0, 2V, hope to have not created more damages...
I have a couple of questions
1) this charger should have a fuse but I don't see any, is it normal ??!!
2) It is a model with dual-mains-voltage selector, when I opened it the switch fell apart and I'm not sure if I put back in the slider the two contact springs correctly, do you have any pics which shows that selector, I haven't?