I found a piece of PCB as the picture shown

Thread Starter

LAOADAM

Joined Nov 21, 2018
518
It can be a charger board?
The 1A fuse burnt, and a 10A fuse burnt too, when I hooked a 110V ac at the two soldering spots which indicated 'ACINPUT', and then I realized it is a 25V capacitor.
My question is why don't other parts burn?
I measured the 4 1N5404 all good, the C is also good.
1 pcb.PNG
 

MisterBill2

Joined Jan 23, 2018
8,736
Given that the capacitor rating is only 24 volts it is not likely that any of the parts were not damaged. So now you most likely have a piece of trash. Yaakov is correct. it was a full wave rectified power module. The parts thatdid not burn probably failed befor the fuses popped.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
518
It is just a full wave rectifier and a filter capacitor. The input is probably from a transformer, I would guess ~12VAC. It has nothing else, no regulation or protection.
Thanks.
That's why I got confused.
All components are still good, where the short happened?
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
518
Given that the capacitor rating is only 24 volts it is not likely that any of the parts were not damaged. So now you most likely have a piece of trash. Yaakov is correct. it was a full wave rectified power module. The parts thatdid not burn probably failed befor the fuses popped.
Thanks.
The all parts measured on board shown good.
 

Tonyr1084

Joined Sep 24, 2015
5,966
Far too little information for us to explain why things happened. Fuses blew. Question: Where are the fuses? I only see four diodes and a capacitor. Were the fuses before or after the board? Was one before and one after? A lot of difference - all matters.

Do you know how to check a diode? I only ask because sometimes people come here for help and speak of things that they may not fully understand, thus, they may say things like "the part tests good". So I only ask because others before you have sometimes been wrong about what they have, tested or did.

In case you don't know how to check a diode - with that board I'd disconnect it from the transformer. Then each diode needs to be checked with a meter that has a diode check setting. Each diode must be tested in Forward and in Reverse current tests. A good diode such as the 1N4007 I have in my hand right now (except for typing) tests good with the positive lead on the anode end (the end opposite to the white line). It reads 0.521V on diode check. When I reverse the test leads I get .OL v meaning "Over Limit". The meter can not detect any voltage passing through the diode when it's blocking current. Each diode needs to be tested that way. I don't think the capacitor will change any readings. But if you're unsure, remove each diode and carefully note their orientation (white bar end).

Let us know what you've found. Keep in mind I'm assuming you might have made a mistake when testing the diodes. Not because I think you're not smart - but because others have made that very mistake. It's not uncommon for beginners to test a diode and think it's good when it's not. And a shorted diode could very well be the reason why a fuse or two blew.
 

Tonyr1084

Joined Sep 24, 2015
5,966
Just for edification: A 3300µF cap can deliver a lot of current to the DC side of the circuit. I'm suspecting that the 10 amp fuse was after the power board and the 1 amp fuse was before the transformer or before the power board. To me this suggests a shorted diode. I've had that happen to me before.
 
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