"easy" PSU repair

[ktmmotocross]

Hello.
I try to learn repairing PSU. I watch many repair and instructional video, so i know how it works.

But i cant figure aut what is whag with this easy PSU

The output voltage must be 12V, but its about 5V and is oscilating from 3V-6V

Can somebody lead me to bad component and little teach how to find it?

That diode must be on the other side but have broken leads so i solder it to other side

[stj]

Re: "easy" PSU repair

that bullshit with the fuse is unwise - you have no idea how much current it's drawing.

[ktmmotocross]

Re: "easy" PSU repair

forget about that fuse. if it blow i throw it to bin.
i just need to learn how to repair it, and how trouble looks like

i think that is problem with regulation but how to check optocoupler, how to check that U3 - TL431 and other components

[ktmmotocross]

Re: "easy" PSU repair

actually i see from top224 datasheet sample diagram that are two diodes on primary, but one of them is i see a zener diode

when i measure components on this PSU i see that this two diode was shorted, so i replace it with two normal diodes.
how can i know the value of that zener diode when i dont have original diode

[budm]

Re: "easy" PSU repair

Check the small lytics cap on the primary side, that is the startup/running cap.
You cannot test that snubber diode with your meter, that Zener is about 200V typical and it is made that way with back to back condition, put the original one back in place. Do not just put in regular diodes in place!

[ktmmotocross]

Re: "easy" PSU repair

from top datasheet i check that i it mostly 200V zener som i put another as the way datasheet shows, but still have oscilation around 5V

i removed that cap from board and test it
it is 100uf/25V and testing shows 98uF ESR-0.88ohm Vloss- 1.7%

[budm]

Re: "easy" PSU repair

OK, I see the two diodes in your pictures now, they are individual diodes not all in one body type.
So if both of those two snubber diodes shorted out, if they were then I would expect the IC to be damaged and I will expect it to have any output in the cold side..
The TO-220 diode in the cold side is mounted like that on the bottom side of the board? and that Diode is OK, correct?
If you measure the DC V between the two legs of that small startup/running cap, it is going up and down too, correct?

[ktmmotocross]

Re: "easy" PSU repair

The output diode is mounted correctly and is ok. DC voltage on small startup capacitor moves between 5,15V and 5,35V

[R_J]

Re: "easy" PSU repair

What do you have jumpered here (yellow box) Is there a resistor on the other side?

[ktmmotocross]

Re: "easy" PSU repair

What do you have jumpered here (yellow box) Is there a resistor on the other side?

no thats just a fuse that was blown, so i jumped it. i dont want to use this psu anymore, just repair it to learn something

and its white box fuse, just lighted by bulb

[R_J]

Re: "easy" PSU repair

Look at the picture. I am looking at the wire on the ic

[ktmmotocross]

Re: "easy" PSU repair

sorry i was not see that u moded the picture. it was just trace ripped off so i replace it with wire. on the other side is trace connected to starting capacitor so i make wire trace to it

i know it is a mess, but i just want to repair it, learn from it and than i just take components from it

[ktmmotocross]

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

[R_J]

Re: "easy" PSU repair

Check the voltage on TL431, then check the voltage on the 2 pins of the optocoupler cold (secondary) side
Then check the voltage on the 2 pins of the optocoupler on the hot (primary) side with meter ground on bridge rectifier (-)

[ktmmotocross]

Re: "easy" PSU repair

here are the measurements

[sam_sam_sam]

Re: "easy" PSU repair

here are the measurements

When you are doing these voltage measurements where are your meter lead at

[ktmmotocross]

Re: "easy" PSU repair

just as u wrote. on hot side i put - lead to - on rectifier

[ktmmotocross]

Re: "easy" PSU repair

can be optocoupler tested with two multimeter in diode mode like mosfet?

in diode mode i dont have any readings on transistor side. on diode side i have in one direction reading around 1000 and nothing on other polarity

when i using two multimeters in diode mode, nothing happend when i try to activate the optocoupler

[ktmmotocross]

Re: "easy" PSU repair

i made a test circuit with 6.5V PSU and multimeter in diode mode and optocoupler was working.

[R_J]

Re: "easy" PSU repair

It looks like you have 0 volts on the opto, so the internal led is not lit, I believe you should have at least 1 - 1.5 volts
I can't see how the traces are run so its hard to diagnose. The diode in the picture covers the traces.
Is the circuit close to the diagram I posted ? does one of the pins of the opto connect to the 12 volt output?

What is the number on the optocoupler?