newb trying to fix pcb

[robowen]

Hi Everyone.
I have a pcb from a Range Hood I'm trying to fix.
It would help me to find out which component caused the blow out.
Heres 3 pics to have a look at to see what you think. Theres no damage to the components themselves all the damage seems to be on the circuit board side.
Couldn't see any moisture in there, no insects etc, so Im not sure why it blew.
So which components should I replace ?

Thnx in advance for your replies.

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[DerStrom8]

It looks to me like it was the relay (I think that's what the large black thing on the left-hand side of the center photo is). You probably had a sort of arc flash in there that fried the contacts. That's just my guess, anyway.
Der Strom

 

[SABorn]

I slightly disagree, the thing DerStrom8 talks about is a transformer and there is 4 relays being the brownish rectangles stacked side by side.

For some reason it has turned the tracks on the board into fuses, and these will need to be repaired as well, a short length of plastic coated wire soldered between the remaining points will fix this, but the cause of the failure i dont know and would require some testing to isolate the cause.

I dont think looking at a photo will solve this and it really is a hit and miss way of repairing something.

Considering this has mains voltage power applied to it, you might be best not to attempt a repair without some sound knowledge of what you are doing.


Edit:- on a closer inspection it looks as though the mains active rail has burnt out, and this could imply a fault off the the board where something else has drawn excessive current and fused the track.

Pete.

 

[pfofit]

A lot of the new appliances have forgone fuses and therefore the main breaker is the only protection you have .

Hence if you have a short, such as a faulty element arcing to the oven cavity, then the circuit board becomes the weakest link. As the main breaker is likely 30 to 40 amps. In addition the infinite switch, the switch marked 1 to 10, sometimes also goes bust as it's meant to handle 20-30+ amps and not a dead short which may give infinite current until the mains open.

Sometimes it's just the solder joints becoming cold weak joints, heat up and then blow their guts like your images.
cheers

 

[DerStrom8]

I slightly disagree, the thing DerStrom8 talks about is a transformer and there is 4 relays being the brownish rectangles stacked side by side.

Sorry, I was in a hurry and didn't get to take a very close look at the board. I mistook the "black thing" for a relay, and the "brown things" for capacitors. You are right, Pete. Sorry for my mistake, and thanks for correcting me.
Der Strom

 

[tunedwolf]

The transformer is a short proof type by the look of it, which is good. The relays are all unprotected and switching right off the incomming mains unfortunately, a dumb design plan, and dangerous in my opinion. The problem you have is off board without a doubt, however as a result of the poor design, the board became the "fuse". Something about made to a price comes to mind...

You will need to clean up the carbon, replace the tracks that are blown with short lengths of wire and replace whatever relay(s) took the "bang" and then find your short circuit in the appliance before trying it again.

rgds

 

[robowen]

Appologies for the poor quality pictures.
I didnt have my camera with me when I needed some info. I'll try to get better pictures.
Thanks for the safety tips, I do have some experience working with circuit boards albeit a good few years ago.
Plus I currently hold a restricted electrical licence, though this kind of work is not my usual thing.

TBH fixing this would give me hobby, plus would save me around $200 in replacing the whole cooker hood.
I thought about finding a replacement circuit board, but theres no name on this hood and no part number, so finding a new one is out of the question.

I think the cause may have been the 50w halogen popping that caused the board to go as well....maybe you guys will disagree ! They both went at the same time.

From the components on the board...transformer / bridge rectifier / capacitors / relays...who's your money on ?

 

[SABorn]

Your restricted electrical licence, must be very restrictive, as the first thing you should be looking for is a fault else where other than the circuit board.

I would guess something has shorted to ground or a direct short between active and neutral.

Tracks dont just vaporize as fuses for no reason, and the track only goes to a relay set of contacts, so i fail to see how the problem is on the board, well not the initial problem anyway, there might be other damage to the board now, but the inital problem still remains off the board.

Pete.

 

[SABorn]

Been pondering for days ...............what the hell is " FADOS7F1 " ???????.

Pete.

 

[Mickster]

"Weak Pete, your search-fu is" - Yoda.

It's one o these:
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