Help Identifying Components on Power Board

Thread Starter

jaydnul

Joined Apr 2, 2015
152
I have a switch mode power supply and need help identifying a couple parts:

I've identified 6. as a schottky diode and 4. is the transformer.

2. is a big .33uF cap, but what is that doing right near the AC mains input? It looks like it is directly in series between the mains lead and everything else.

1. (the big rectangular component on the left) is my biggest question. What is it? Is it the micro controller for the pulse width modulation? I can't find any info on the part.

3. Is this just a big inductor for the main part of the switch mode supply?

5. These look like fat capacitors and have the capacitor symbol etched in silk screen on the board, but they don't have any writing on them. Something tells me they are MOVs, is this correct? Would they just be for over voltage protection?

Thanks
 

ian field

Joined Oct 27, 2012
6,539
I have a switch mode power supply and need help identifying a couple parts:

I've identified 6. as a schottky diode and 4. is the transformer.

2. is a big .33uF cap, but what is that doing right near the AC mains input? It looks like it is directly in series between the mains lead and everything else.

1. (the big rectangular component on the left) is my biggest question. What is it? Is it the micro controller for the pulse width modulation? I can't find any info on the part.

3. Is this just a big inductor for the main part of the switch mode supply?

5. These look like fat capacitors and have the capacitor symbol etched in silk screen on the board, but they don't have any writing on them. Something tells me they are MOVs, is this correct? Would they just be for over voltage protection?

Thanks
2 & 3 are mains input filter components, the capacitor is directly across the mains and must conform to certain specifications.

The inductor is a common mode choke - windings are in series with both live and neutral.

5 is a high voltage capacitor, usually from one or both mains wires to earth - although there man not actually be an earth on the system. These parts also have very specific ratings that must be complied with.
 

mcasale

Joined Jul 18, 2011
210
My guess is that the "big" cap, #2, is actually part of a line filter.
The inductor, #3, is probably part of the filter as well - maybe a balun.
 

ian field

Joined Oct 27, 2012
6,539
My guess is that the "big" cap, #2, is actually part of a line filter.
The inductor, #3, is probably part of the filter as well - maybe a balun.
Baluns are usually found between coaxial cable and balanced twin.

Balun is short for balanced/unbalanced transformer.

The inductor is a common mode choke.
 

Jony130

Joined Feb 17, 2009
5,176
1 - switching transformer
2 - capacitor a probably X type
3 - common mode choke
4 - switching transformer
5 - capacitor, probably Y type
6 - linear/switching voltage regulator

And this LG device name is ??
 

AnalogKid

Joined Aug 1, 2013
8,492
Switching power supplies generate a lot of high frequency electrical noise, and some of that noise is conducted back down the power cord. There are rules about how much noise is allowed out. #2 is a noise filter capacitor designed and built to be connected directly across the AC power input. #3 is a common-mode choke, a dual inductor that looks like a transformer but is not. The #5 blue guys sprinkled around also are noise filter components. These are the parts that make the supply "legal".

U101, the 8-pin DIP part with one pin missing, is a Power Integrations switching power supply part. It is the controller and the switching power transistor all in one, and drives the primary side of #4, the main transformer. The dashed white line contains all of the parts connected in some way to the power line - the dangerous area. Note that the line runs under the middle of the transformer and the middle of U201, an optical coupler. These are the two parts that bridge the isolation barrier between the supply primary and secondary sides. Some of the blue noise filter caps also bridge the line. Like #2 they are built and tested for high voltage operation.

ak
 

Thread Starter

jaydnul

Joined Apr 2, 2015
152
Here is a picture of the back:


The surface mount IC on the back is a "pulse ccfl inverter controller (MP10072ES). I can't find any info on this IC, no datasheets online. What does it do exactly?

Also, when you say "switching transformer" what do you mean? It's not a term I'm familiar with and it doesn't show any meaningful results in google.

This is for a computer monitor, LG W2046T

Thanks for all the help so far
 

Dodgydave

Joined Jun 22, 2012
9,206
Looks like its a inverter transformer to feed the fluorescent tubes, with series capacitors.

The whole pcb converts the mains voltage to dc, and this is used to make an high voltage oscillator to feed the fluorescent tubes on the monitor, it probably provides other voltages, the whole pcb is split into two halves by an opto-coupler ( 4 pin chip) in the middle, this monitors the output voltage and controls the feedback to the pwm chip.
 
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Thread Starter

jaydnul

Joined Apr 2, 2015
152
Cool. What are some troubleshooting steps I should take? All the caps seem to be fine but it only outputs power for about 5 seconds, then shuts off.
 

SLK001

Joined Nov 29, 2011
1,548
Cool. What are some troubleshooting steps I should take? All the caps seem to be fine but it only outputs power for about 5 seconds, then shuts off.
You have problems elsewhere in your monitor. What is occuring is a safety shutdown of the power supply after 5 secs (usually less than this). I would say that one of your CCFL tubes is bad.

Somewhere on your board's connecters is some signal like "PWR_OK" or something like that. You can jumper this to +5V (which should be there) and operate the board without any connections except input power.
 

Dodgydave

Joined Jun 22, 2012
9,206
Sounds like there is a short on the output side of the inverter, possibly tubes or whatever else is being used. Can you measure the voltages with the outputs disconnected, and then see what happens as you connect them back one at a time.?
 

Thread Starter

jaydnul

Joined Apr 2, 2015
152
Yep, I'll do that when I have some spare time this week. Thanks for all the help, I'll post an update after I work on it.
 
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