Help figure out burnt up resister values after fireworks(:

[sdinelli]

Hello all
fun times here tinking with the electronics.

Minifridge PSU blew up. i replaced a diode bridge rectifier and one mosfet that was shorted. a blown fuse and the varistor.
( yes i know i should have replaced both mosfets. Im learning)
i didnt really find anything else wrong so i plugged in and got some high pitch sounds and after 5 secs fireworks went off.
Two resistors fried.
trying to figure out the values of them. No way to tell but hoping someone can give me a general safe bet based on knowledge of switching PSU's.

ive also found a 4.7cap measuring only 2.3uf, shorted zener diode and out of spec 10ohm(i think) resistor attached to that rail.
The other diodes in teh area are measuring OK

See picture. ive circles all the components red.
please let me know what you think happened and what the values could be. and anything else to check.

Thank you in advance

[CapLeaker]

Re: Help figure out burnt up resister values after fireworks(:

So what are the markings on the Mosfet? Specifically the one with the burnt resistors. If the Mosfet is shorted to the gate, you also have to look at the whole gate drive circuit!

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

Base and collector shorted on the fet
pins 1 &2
the diodes in the bridge rectifier are testing fine, caps look ok.
im afraid the resistors in there might be fried. i have to pull them to test.
not getting a proper reading.

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

They were two 150k resistors. tested good

[ReeceyBurger123]

Re: Help figure out burnt up resister values after fireworks(:

I’ve had good luck cutting burnt resistors in half that are open and then doubling the resistance of whatever I can test ��

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

well as is, one measured 375ohm and the other 2.4kohm
i cut the 2.4ohm in half not really sure how to test now lol

[R_J]

Re: Help figure out burnt up resister values after fireworks(:

The resistors have location numbers, which are you looking for? ie: R04 = 10Ω, D10 should be the same as D12 (1N4148)
R36 2.7K, Can you read any of the colors on R35? R35 could be 2Ω

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

The resistors have location numbers, which are you looking for? ie: R04 = 10Ω, D10 should be the same as D12 (1N4148)
R36 2.7K, Can you read any of the colors on R35? R35 could be 2Ω

R35 & R36 are the burnt ones.
Was unable to read anything, the whole outer was burnt away
How did you know that was D12's part number???

[lotas]

Re: Help figure out burnt up resister values after fireworks(:

Here is a better photo, you can see. https://4chanarchives.com/board/diy/thread/931526
https://i.imgur.com/pjvEuZ5.jpg

[R_J]

Re: Help figure out burnt up resister values after fireworks(:

D12's number is clear in your picture. Check this thread, it may help https://www.badcaps.net/forum/showth...ghlight=cd-110

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

wow thanks alot
ill see what parts i can scavenge and let you know how it turns out.

[CapLeaker]

Re: Help figure out burnt up resister values after fireworks(:

I've had good luck cutting burnt resistors in half that are open and then doubling the resistance of whatever I can test ��

Interesting idea… I got to try that! Thanks buddy!

[ReeceyBurger123]

Re: Help figure out burnt up resister values after fireworks(:

Interesting idea… I got to try that! Thanks buddy!

It's worked for me lots of times haha, nothing I've done this too yet when I've been stuck has blown up major

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

how much amp fuse should i put in there?
i pulled out a 3A but i may have replaced it wrong the first time.
i have 3A and 15A in stock.

I was able to scavenge the 10ohm resister and teh zener diode.
i have the extra mosfets left over from last time. (in case i failed the first)
Just need to get the burnt resistors. May have to just order them.

[momaka]

Re: Help figure out burnt up resister values after fireworks(:

how much amp fuse should i put in there?
i pulled out a 3A but i may have replaced it wrong the first time.
i have 3A and 15A in stock.

3A should do the trick.
Just make sure to use a series incandescent bulb in series with the PSU after you have replaced all of the parts and are ready to test it. Like this:
https://www.badcaps.net/forum/showpo...4&postcount=70
This should prevent you from blowing fuses and other parts again if the PSU still has issues.

Just one note about the above circuit: you cannot test the PSU with any load. In some cases, a 40-60W bulb may be inadequate to make the PSU start up. In such cases, you might have to go up to 100W... which can be hard find nowadays, due to incandescent bulbs being phased out. But 40W appliance / "decorative" incandescent bulbs can still be found in most hardware stores. If that's all you have, you can parallel 2-3 40W bulbs (which would be equivalent to a 80W or 120W bulb.)

[sdinelli]

Re: Help figure out burnt up resister values after fireworks(:

Hello everyone,
i just wanted to say thank you for all your help.
i ended up replacing the two Fets, two burnt up resistors, a diode, capacitor and
IT WORKS!

I first tested with the light bulb contraption. got nervous because it was making a whine. but bulb didnt light up. so i measured voltage and was getting all of them so i connected it normally and success... been working all week.

THANKS!

[sam_sam_sam]

Re: Help figure out burnt up resister values after fireworks(:

Good work
One more item that does not end up in a landfill

[sam_sam_sam]

Re: Help figure out burnt up resister values after fireworks(:

IT WORKS!

I first tested with the light bulb contraption. got nervous because it was making a whine. but bulb didnt light up. so i measured voltage and was getting all of them so i connected it normally and success... been working all week.

THANKS!

Sometimes you have to use a higher wattage light bulb for it work more like it would plugged directly into the wall

Here is a post where I used the light bulb contraption ( instead of the fuse ) to troubleshoot a machine that was blowing fuses starting on post #9

https://www.badcaps.net/forum/showth...ht=sam_sam_sam

I use this light bulb contraption when I have a device that has blown fuse in it so I can see how bright the light bulb is so I know just how much of a possible short it might have