Samsung LA22A350C1, unable to power up

[vernond]

Hi,

would like your help in troubleshooting this 22" Samsung LCD TV.

The defect, unable to power up the TV.
The power light is there but when the power button is pressed, the power light remains illuminated and there is no picture and no sound.

Have check the output voltages from the power supply to the mainboard and found all voltage to be available. Does this confirm the mainboard is the defective?

Thanks for your input.

[budm]

Re: Samsung LA22A350C1, unable to power up

What DC Voltage do you get at the heatsink where the two diodes are attached to, black probe on the chassis, red probe on the heatsink

[vernond]

Re: Samsung LA22A350C1, unable to power up

What DC Voltage do you get at the heatsink where the two diodes are attached to, black probe on the chassis, red probe on the heatsink

Voltage on the diode heatsink is 22.70 volt. What is the function of this two diodes? What is the significance of measuring the voltages at this point?

I've attached a picture of the power supply PCB with the measured voltages.

[selldoor]

Re: Samsung LA22A350C1, unable to power up

Bud will have to answer your question

With a known working source connected (PC) or DVD) have you tried to see if there is anything at all on screen by shining a flashlight at an angle.
What is the part number on the inverter transformer.
BL is the back light on signal pin.
You could try a 500ohm resistor between the bottom 3.~ pin and the BL on- to see if it lights up the back lights.

Pictures are not really clear enough for troubleshooting - should look like this
Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246

[vernond]

Re: Samsung LA22A350C1, unable to power up

Ok thanks for the reply will update you shortly.

[budm]

Re: Samsung LA22A350C1, unable to power up

That is the voltage for running the backlights inverter circuits, had to make sure we do have the power feeding it, so next we need to find is the BL_ON (Backlights On) signal which is generated by the main board.
I will need good clear pictures of the top side and the bottom side of the power supply-inverter board as a whole and also in 1/4 section so we easily see and read the components and traces.

[vernond]

Re: Samsung LA22A350C1, unable to power up

I've uploaded more pictures, I hope this is clear enought.

I've tried to power the TV while connecting it to a PC but still the TV does not come out of standby mode.

[selldoor]

Re: Samsung LA22A350C1, unable to power up

Hi- sorry I thought when you had all the voltages it would be working more than it is. You could still try the jumper.
Budm probably meant the bottom in quarters he can follow and understand circuits. Try to get them without flash washing it out.
I have had a quick look but apart from a few odd solders cant see much.
Maybe getting ahead but one easy test you can do is on the secondary windings of the two inverter transformers - it will eliminate one problem. No power to set meter on ohms 2000 test the two pairs of secondaries on each transformer. S1 to S2 and S3 to S4
Couldnt find the exact one but all the tms**** seem to look like this one
http://www.lcdparts.net/TransformerD...ProductID=3708

[budm]

Re: Samsung LA22A350C1, unable to power up

Can you do 1/4 section for the bottom side, trying to trace the B+ (22V) feeding the two SMD Dual MOSFETs (the device with 4 small legs on one side and big tab on the other side) that each drive the inverter transformer?
By the way, is fuse F101 (round red cylinder, it is the fuse for the inverter circuits) check out less than 1 Ohm? You can check the DC on the output side of the fuse at jumper J207 (fuse check point as printed on the board) and the chassis ground.

[selldoor]

Re: Samsung LA22A350C1, unable to power up

Budm -I have tried following out the traces from the mosfets
(just for a bit of practice as I dont know what I am doing)
having done it I dont know what it means.
One seems to go through a system of switching transistors
Have you formed an opinion on the failure rate on these.
I always want to blame them for the unknown fails on main boards but we get few reports of them being bad but does anyone test them?

Vernond - Can you check out resistor R10? Blue Brown Black and Gold - May be a makers mark or dust but there is a mark on the side near the cap.Burn? chip?

Also check J214 solder looks a bit odd but may just be the pic.

[budm]

Re: Samsung LA22A350C1, unable to power up

I am waiting to find out if the inverter fuse is good or not, the B+ after fuse goes to those two MOSFETs.
The red trace you marked is the secondary ground, the big trace above it is fed by the fuse, that is the B+ LINE for the MOSFETs.

[vernond]

Re: Samsung LA22A350C1, unable to power up

Thanks for the input will update you later.

[vernond]

Re: Samsung LA22A350C1, unable to power up

Hi- sorry I thought when you had all the voltages it would be working more than it is. You could still try the jumper.
Budm probably meant the bottom in quarters he can follow and understand circuits. Try to get them without flash washing it out.
I have had a quick look but apart from a few odd solders cant see much.
Maybe getting ahead but one easy test you can do is on the secondary windings of the two inverter transformers - it will eliminate one problem. No power to set meter on ohms 2000 test the two pairs of secondaries on each transformer. S1 to S2 and S3 to S4
Couldnt find the exact one but all the tms**** seem to look like this one
http://www.lcdparts.net/TransformerD...ProductID=3708

I've checked the secondary windings of the inverter transformer and they seem to have a resistance about 800 ohms on all 4 windings. The primary windings also seems to be ok with 1 ohm resistance. Have not jumped the pins as you suggested

[vernond]

Re: Samsung LA22A350C1, unable to power up

Can you do 1/4 section for the bottom side, trying to trace the B+ (22V) feeding the two SMD Dual MOSFETs (the device with 4 small legs on one side and big tab on the other side) that each drive the inverter transformer?
By the way, is fuse F101 (round red cylinder, it is the fuse for the inverter circuits) check out less than 1 Ohm? You can check the DC on the output side of the fuse at jumper J207 (fuse check point as printed on the board) and the chassis ground.

I've check the continuity of the B+ tracks to the Dual MOSFETs and they seem to be ok with a low resistanc reading.

F101 is also ok with 1 ohm resistance reading.

[vernond]

Re: Samsung LA22A350C1, unable to power up

Budm -I have tried following out the traces from the mosfets
(just for a bit of practice as I dont know what I am doing)
having done it I dont know what it means.
One seems to go through a system of switching transistors
Have you formed an opinion on the failure rate on these.
I always want to blame them for the unknown fails on main boards but we get few reports of them being bad but does anyone test them?

Vernond - Can you check out resistor R10? Blue Brown Black and Gold - May be a makers mark or dust but there is a mark on the side near the cap.Burn? chip?

Also check J214 solder looks a bit odd but may just be the pic.

I think you are refering to R101 instead of R10. Im getting a reading of 51ohms across this resistor which corresponds to the reistors color code(Blue, Brown, Black)

J214 was checked for continuity and found to be fine.

[vernond]

Re: Samsung LA22A350C1, unable to power up

Bud will have to answer your question
You could try a 500ohm resistor between the bottom 3.~ pin and the BL on- to see if it lights up the back lights.

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I've tried what you suggested but with no change. The TV would still not come out of standby nor did the backlights illuminate.

I've check though the main board's fuses and all of them seems to be intact.

I did notice a crack in the IC 108, 1117 regulator IC, as in the attachment. This component seems to have been replaced. Will check or replace this IC.

Do you guys suspect the mainboard or power supply board to be faulty?

[tom66]

Re: Samsung LA22A350C1, unable to power up

That IC is most likely defective; perhaps it's a common failure and was replaced in the factory?

[vernond]

Re: Samsung LA22A350C1, unable to power up

That IC is most likely defective; perhaps it's a common failure and was replaced in the factory?

I've still not replaced this IC since it is not available locally would have to get it from ebay. The IC is a 1117, which appears to be a 3.3V regulator, the strange thing though is that I'm getting 3.3 Volts at the input of the IC.

I dismantled the switch assembly and checked the switches including the power switch which gives me a 0 to 100ohm reading. I dont have the remote control for the set, not sure if the remote control would solve the problem.

Tried to source for the mainboard part number BN41-00988 on ebay and a few search engines and it appears only one guys is stlling at USD100 something which is not worth.

[retiredcaps]

Re: Samsung LA22A350C1, unable to power up

The IC is a 1117, which appears to be a 3.3V regulator, the strange thing though is that I'm getting 3.3 Volts at the input of the IC.

What is the complete part number on that IC? The 1117 indicates it is a voltage regulator, but usually you need to read all the part numbers to determine if it is a fixed or adjustable regulator.

[vernond]

Re: Samsung LA22A350C1, unable to power up

What is the complete part number on that IC? The 1117 indicates it is a voltage regulator, but usually you need to read all the part numbers to determine if it is a fixed or adjustable regulator.

It just reads DC 1117. Not sure if 'DC' is part of the part number.