"easy" PSU repair

[petehall347]

Re: "easy" PSU repair

I would expect the MOSFET inside the SMPS to be damaged since the snubber diodes shorted out and also blew the fuse. The strange part is that OP is indicating output Voltage on the cold side so something is switching in the HOT side, at this point I would suggest to replace the IC and the OPTO. It is also strange to have BOTH snubber diodes shorted out.

depends if measured in circuit or not i would think .

[ktmmotocross]

Re: "easy" PSU repair

can be that TOP ic measure outside of board?

all traces looks ok

with - lead on - of rectifier o dont have any voltage on TL431

[R_J]

Re: "easy" PSU repair

can be that TOP ic measure outside of board?

all traces looks ok

with - lead on - of rectifier o dont have any voltage on TL431

And you won't measure any voltages that way. but that is NOT what I asked you to check.
Please check the voltages with meter ground on Bridge [-]:
1
2
3
4
5

[ktmmotocross]

Re: "easy" PSU repair

sry. my fault

1 - 0.3V
2 - 5.3V
3 - 5.2V
4 - 0.0V
5 - 315V

[R_J]

Re: "easy" PSU repair

Having 0 volts on test point #1 tells me there is no voltage being generated by the feedback winding. Check that that winding is not open and check that the diode between the winding and the opto is good. Also the smd caps could be shorted, the one across the winding would need to be remove to be tested.
The 5.3 volts on Test point #3 is coming FROM the control pin of the ic (internaly generated). 5.2v on test point 2 tells me the trace between the control pin and the opto is good.
If the main output (12 volts) is about half (~5v), that tells me the feedback voltage should be at least a 2-3 volts,

when the power supply is working normal I would expect the feed back voltage to be about 10 volts

[R_J]

Re: "easy" PSU repair

Did you find anything with this power supply?

[ktmmotocross]

Re: "easy" PSU repair

does anybody know from pictures what leads is for aux and what for primary winding?

[R_J]

Re: "easy" PSU repair

Easy, here you go

[ktmmotocross]

Re: "easy" PSU repair

so we have our winner

the aux winding is open

thanx for help guys

[R_J]

Re: "easy" PSU repair

Oh well, about the only part you can't get.

[momaka]

Re: "easy" PSU repair

Oh well, about the only part you can't get.

True.
But that doesn't mean the O/P can't try to open the transformer and fix the burned out aux winding. A lot of work for a small adapter? -Yes. Then again, this adapter is being fixed for learning purposes, is it not?

BTW, a suggestion to ktmmotocross:
If you're going to bridge the fuse in the future, then at least use a the series incandescent bulb trick to limit current in case something goes wrong. Details here:
https://www.badcaps.net/forum/showpo...4&postcount=70

Otherwise, you could end up with lots of smoke and a bunch of melted wires on the floor - which is both a fire hazard and an electrical hazard for you.
It's fun to fix power supplies, but make sure you're safe too. On that note, I also encourage people to wear safety glasses when testing things. High-power diodes and transistors tend to go out with a big bang and could send flying shrapnel parts right in your eyes. Venting electrolytic caps can also be dangerous.

[R_J]

Re: "easy" PSU repair

True.
But that doesn't mean the O/P can't try to open the transformer and fix the burned out aux winding. A lot of work for a small adapter? -Yes. Then again, this adapter is being fixed for learning purposes, is it not?

BTW, a suggestion to ktmmotocross:
If you're going to bridge the fuse in the future, then at least use a the series incandescent bulb trick to limit current in case something goes wrong. Details here:
https://www.badcaps.net/forum/showpo...4&postcount=70

Otherwise, you could end up with lots of smoke and a bunch of melted wires on the floor - which is both a fire hazard and an electrical hazard for you.
It's fun to fix power supplies, but make sure you're safe too. On that note, I also encourage people to wear safety glasses when testing things. High-power diodes and transistors tend to go out with a big bang and could send flying shrapnel parts right in your eyes. Venting electrolytic caps can also be dangerous.

I can see you did'nt look at the picture of the board... encapsulated transformer good luck opening one of these

[ktmmotocross]

Re: "easy" PSU repair

True.
But that doesn't mean the O/P can't try to open the transformer and fix the burned out aux winding. A lot of work for a small adapter? -Yes. Then again, this adapter is being fixed for learning purposes, is it not?

BTW, a suggestion to ktmmotocross:
If you're going to bridge the fuse in the future, then at least use a the series incandescent bulb trick to limit current in case something goes wrong. Details here:
https://www.badcaps.net/forum/showpo...4&postcount=70

Otherwise, you could end up with lots of smoke and a bunch of melted wires on the floor - which is both a fire hazard and an electrical hazard for you.
It's fun to fix power supplies, but make sure you're safe too. On that note, I also encourage people to wear safety glasses when testing things. High-power diodes and transistors tend to go out with a big bang and could send flying shrapnel parts right in your eyes. Venting electrolytic caps can also be dangerous.

I know that but as i wrote i dont mind if it blow as i dont want to use it even if it was reapired. i just wanna learn from it

[R_J]

Re: "easy" PSU repair

If you are going to jump a fuse like that for testing only, just use one thin strand of wire. somthing like #30 gauge. If the power supply was repaired, then you should replace the fuse with the correct type.
There might be a different number stamped on the transformer side or maybe under that label? if you did want to try to find one.

[momaka]

Re: "easy" PSU repair

I can see you did'nt look at the picture of the board... encapsulated transformer good luck opening one of these

As long as it's not epoxy-impregnated (like TV flyback traffos), it *can* be opened. I'm not saying it will be easy or look pretty afterwards (most likely will have to take a hacksaw / dremel to the outer plastics.)

If you are going to jump a fuse like that for testing only, just use one thin strand of wire. somthing like #30 gauge.

+1
A thin wire should at least partially limit the current.

I know that but as i wrote i dont mind if it blow as i dont want to use it even if it was reapired. i just wanna learn from it

You're missing the point.
It's OK to want to learn from something and try not to waste too much time or resources/parts on it. But bridging fuses with thick wire and plugging the DUT in the wall can be DANGEROUS. What if some component blew and shrapnel from it got into your eye? What will you learn then and would it be worth getting injured for that?!

In your case, you mentioned you were measuring current with your multimeter and the PSU was barely drawing anything. Well, what if it didn't and something went wrong while measuring with your multimeter? Now your multimeter would get damaged too.

It's like trying to learn how to ride a motorcycle when you don't even know where the throttle, breaks, and gears/clutch are. Surely before you jump on it, you will want to know where these things are and how they work. Otherwise, you'll just be another video submission for one of those Fail channels (Fail Army, Fail Blog, etc.)... and that's if you don't end up breaking something.

If you want to learn in a more proper way, you should take all of the suggestions mentioned in this thread and learn from those.

[petehall347]

Re: "easy" PSU repair

wondering if the transformer became a fuse and ended this story ?

[eccerr0r]

Re: "easy" PSU repair

Surprised it was the aux wiring, so I kind of doubt that it was the story ender. I'd more think of the aux winding opening up due to manufacturing defect and causing the PSU to go open loop and burn the fuse with high V*I draw.

Sometimes the broken spot is just where the winding is attached to the pin and may get lucky repairing it there, but even this I don't have much faith in repairing transformers...

[SoporteHR]

Re: "easy" PSU repair

i checked almost every component on it except optocoupler, U3 and smd capacitors

dont know how to check that U3 and optocoupler

Hello, to test the Octo-couplers, what I do is dismantle it from the PCB, I connect it to a protoboard with the next circuit and I connect a duly polarized LED to the side of the transistor.

When turning on the internal led of the octocoupler, the led should light on the other side.

To test U3, google search, there are hundreds of circuits to connect it in a breadboard and get a voltage of 2.5vdc as a reference. If you get it then it's fine.

Greetings.