"easy" PSU repair

[ktmmotocross]

Re: "easy" PSU repair

must be this led lid when i have lower output voltage than 12V so it dont need to reduce duty cycle?

and why is this duty cycle so low that it even not reach 12V output?

i attach another pictures for u

[R_J]

Re: "easy" PSU repair

If you loose the feedback you want the voltage to go low, If there was a problem with the feedback circuit and the voltage went high, it could reach 20-30 volts which would not be good.

[ktmmotocross]

Re: "easy" PSU repair

so what can be checked next? as i check optocoupler so there must be something bad elsewhere

[R_J]

Re: "easy" PSU repair

This seems to be how the feedback is connected, Are the resistors ok ?
There is a diode across the output, Is this 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

This could also be your problem, they are not regular diodes. one is a tvs diode (P6KE200 or similar) That could be killing the primary waveform, You could try replacing the tvs diode with the resistor/capacitor shown in the top224 datasheet temporarily to see if the output comes up to 12 volts.

[ktmmotocross]

Re: "easy" PSU repair

all resistors chcecked outside of board and is ok

that P6KE200 diode is a zener diode that i replace earlier for just diode that it meant to be

That diode on output is 1A shotky barier diode

across output diode i found broken capacitor. dont have its parameters so i just throw in some capacitor laying around without know its capacity,is it a problem?

[R_J]

Re: "easy" PSU repair

This diode is a 1 amp shottky diode? This should be a Zener diode.
And you replaced the P6KE200 with the proper tvs diode, correct?
Do you mean that chip cap across the output diode? just remove it for now and see if the voltage comes up.

[ktmmotocross]

Re: "easy" PSU repair

yes that diode is 1A shotky, looks like it was nor replaced


that big diode have on it P6KE200A 4702

removed that capacitor but voltage not rises

[R_J]

Re: "easy" PSU repair

You can't have a regular diode across the 12 volt output (My picture post#26)

I see the diode you replaced in your picture above(post#27) Which diode are you replacing? If you look at the schematic, is it VR1 or D1 ?
That diode you are using to replace VR1 is a p6ke200a that should be ok

[ktmmotocross]

Re: "easy" PSU repair

i replaced both diodes VR1 and D1. VR1 is that P6KE200A and D1 i just throw some diode laying around. i check it now and its B360A 3A shotky diode. it's rating is only 60V but it dont blow so it is good :-)

when i remove that 1A shotky diode nothing changes

[R_J]

Re: "easy" PSU repair

What about the diode across the 12 volt output? what is the number on it? I asked about it in post #26 (the one in the yellow box)

[ktmmotocross]

Re: "easy" PSU repair

thats that 1A shotky diode 1N5819

[R_J]

Re: "easy" PSU repair

Have you tried removing it to see if the voltage will come up? It could be breaking down when there is voltage on it.

[ktmmotocross]

Re: "easy" PSU repair

try to remove it but nothing changed

if it is connected in blocking way to plus it can stay there

[stj]

Re: "easy" PSU repair

before this goes any further,
you blew the fuse - did you find what blew it yet?
because that's not related to output voltage.

do you know the current it's drawing from the mains?

[ktmmotocross]

Re: "easy" PSU repair

it does matter?

nothing gets hot so it will be miliamps

[R_J]

Re: "easy" PSU repair

It could be that the top224 is damaged, if everything else seems to check ok

[stj]

Re: "easy" PSU repair

transformer with a short in the primary will still work but draw more current (reduced resistance)

[ktmmotocross]

Re: "easy" PSU repair

it draws less than 0.1 mA. literraly i cannot even measure it because my multimeter dont have that low scale

[R_J]

Re: "easy" PSU repair

Using the bridge (-) as ground, what voltage to you measure on the pins of the top244?
You repaired the trace from the control pin to the capacitor, BUT is the trace from the control pin to the optocoupler ok?

[budm]

Re: "easy" PSU repair

It could be that the top224 is damaged, if everything else seems to check ok

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.