Sanken SMPS

[spdf]

Hi, I have Sanken PSC10089G M SMPS pulled from Lg plasma Tv.

First of all I found bad diode which says n44k on it. Does that mean 1n4400? 6.8V Zener? Looks like an ordinary silicon diode though.

And I have 40 Volt 30A Dual Schotkky Rectifier in question. It reads 0.1V from cathode to anode on both diodes. From cathode to cathode it is not shorted. Is it ok?

Any help will be appreciated

Thanks!

[spdf]

Re: Sanken SMPS PSC10089G M

This is my first time I am trying to repair switching mode power supply that I pulled off from old LG plasma TV. After I am it still not working looking at it every day lol...

Model Sanken PSC10089G M I couldn't find any schematics of it.

At first it was completely dead no output voltage and no standby voltage what so ever. I tried to measure some voltages and I found out that I have ~300V on primary filter caps and that's all. After changing power IC KA7553 standby voltage came a live BUT after trying to powering it on in series with 100W bulb relay clicked and bulb began to shine - dead short. (I disconnected all smps loads and soldered some pull down resistors to start power supply) I literally checked every component with DMM and couldn't isolate any shorted components in circuit so now I am beginning to suspect switch mode power transformer, but I already know from reading this outstanding forum that it is highly unlike that this transformer went bad.

it would be great if someone could give me advice or point out where to look for a clue. ;]

I added photos (please don't mind red square in these photos it's just a personal reminder ).

[spdf]

Re: Sanken SMPS

A little update: today I pulled of the circuit (look atached photo) 3 x K2698 MOSFET'S (that was quite a work...) and FSU10B60 diode all these components are fine.

[stj]

Re: Sanken SMPS

explain "dead short"
if the bulb lit full brightness then the psu works - the problem is someplace else.

[spdf]

Re: Sanken SMPS

I have totally lost...

I have disconnected all load from psu and added pull down resistor to power up psu, at first bulb ligts up and dim away after ~10s relay clicks and bulb is shining in full brightness. So i decided there is a dead short some where in psu circuit? Or isn't it?

[stj]

Re: Sanken SMPS

oh - bulb is in series with the mains - o.k.
well check what parts the relay switches in - then you will probably find the short.

i cant see under the heatsinks, but i think there is a big bridge rectifier under the lower one - check that first.

[spdf]

Re: Sanken SMPS

Is it possible that if I left psu turned on with bulb in series that shorted components will become hot?

[stj]

Re: Sanken SMPS

maybe - it depends what they are.
it's also possible the shorted part with catch fire or explode - so dont leave it alone if you try that.

[spdf]

Re: Sanken SMPS

Is there any possibility that this chip (in photo) is shorted? Is there any way to test it?

[stj]

Re: Sanken SMPS

no idea, but i suspect the problem is a simple but large part - like the bridge rectifier or a diode

[budm]

Re: Sanken SMPS

Well, did you check the bridge rectifier as suggested? The relay supplies the AC to feed the bridge rectifier.
You should also check the resistance between the two outer pins of the bridge rectifier to see if it shows low resistance (<500 Ohms) in both directions.

[spdf]

Re: Sanken SMPS

Thanks for the input!

In diode mode bridge rectifier reads as expected, though resistance of outer pins in circuit is in megaohms range.

Voltage I measured on filter caps is ~300V DC while relay is not activated (does that make sense?). Is it still possible that bridge rectifier produces short?

[PeteS in CA]

Re: Sanken SMPS

If you have 300VDC on the filter caps, I don't think there's a shorted diode in the bridge rectifier. Does the relay act as an on-off switch? Or does if short across inrush limiters after several AC cycles?

[spdf]

Re: Sanken SMPS

Does the relay act as an on-off switch? Or does if short across inrush limiters after several AC cycles?

As an On-off switch.

There is no short if I unsolder pin 6 from power factor correction IC and relay is still turning on.

I managed to find two bad SMD transistors (or it's a diode?) + smd cap in question. Does anyone have a clue what kind of transistors are they and cap?

[stj]

Re: Sanken SMPS

can you see whats written on them?

[spdf]

Re: Sanken SMPS

There is nothing. It's just black ;]

[spdf]

Re: Sanken SMPS

Is it even possible to tell something about these parts without scehmatics? (It's kinda strange that it's impossible to find any information about this smps, or isn't it)

[R_J]

Re: Sanken SMPS

This guy fixed the same board https://www.eevblog.com/forum/repair...s-psc10089g-m/

[PeteS in CA]

Re: Sanken SMPS

It is possible that the normally open relay contacts have welded into the "on" position.