Samsung 231T, recapped, no power, no lights

[kingofcoins]

My search shows no successful repairs on this particular Samsung 213T Syncmaster LCD model. So lets try this one....it started as no lights, no power, no noise; and I found all 10 caps on power and inverter boards were bloated, shorted, or had high ESR's; replaced them all mostly with Pan FM's, but after that still no power, no lights, no noise at all.
I get no voltage at the large cap, both fuses on power board read 0 ohms, and of course no DC voltages out to logic board. There is no visible signs of any burning. The inverter transformers look like they've seen a little heat but then this unit has definitely seen a few hours, was made in Jan 2004. I have d/l'd the repair manual/circuit diagrams. Attached my pics...oh and now that I went over board again, I see a small 22uf x 50v cap NW of the big guy....could this cap give these symptoms ?
So...what should I check next...?

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

I get no voltage at the large cap, both fuses on power board read 0 ohms, and of course no DC voltages out to logic board.

I see a small 22uf x 50v cap NW of the big guy....could this cap give these symptoms ?

If you are not getting voltage at the big main filter cap, check your bridge rectifier for shorts (black rectangular box just below the main cap). Number the pins 1,2,3,4. With power off and lcd unplugged measure the ohms between 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any reading below 30 ohms suggests it is shorted (bad).

The 22uF 50V can be bad without bloating and should be replaced due to guilty by association (as PlainBill would say). This cap plays an important part of the SMPS startup process.

edit: The small cap, however, is not the root cause of why there is 0V DC the main cap. The small cap comes into play AFTER you see (mains x 1.414) DC voltage on the main cap.

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

C111 on the logic board looks funny in the picture? Problem or glare/flash?

[kingofcoins]

Re: Samsung 231T, recapped, no power, no lights

Retired...., thanks...C111 like its mate C102 to the right, have a domed top to the cap, and very much appear to be the manufacturers style of can.
The bridge rectifier legs pairs all read very high resistances.
I'll await some sign of life before I recap the small C603.
What next ?

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

What next ?

On your fuses, what is the exact ohms reading? For example, on mine, they read 0.3 ohms.

How are you measuring DC voltage on the main filter cap? Where are you putting your probes?

edit: I have to ask because a few people in the last couple of weeks were not correctly measuring the main filter cap with their multimeter. Some reported negative readings, some had the probes in the wrong place or jacks in their multimeter.

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

I'm heading out soon, but on one monitor with no power that I fixed, the solder on the AC input (backside) had ring cracks. I reflowed the solder and it worked fine afterwards.

You may want to check the soldering on the backside on all components on the "hot" side of the board.

[kingofcoins]

Re: Samsung 231T, recapped, no power, no lights

Both fuses read a calibrated 0.0 ohms .
Measure the large cap with the power plugged in, meter set on 300VDC, probe the cap legs polarity correctly...in my case 0 VDC.
You may go advanced on this I have some background, and will do my best to keep up.

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

You may go advanced this I have some background, and will do my best to keep up.

See my edit in post #5 for asking. If the soldering in post #6 doesn't help, see if there is AC voltage across the fuse.

Also, if you found a schematic, post the power supply section so we can give more test points.

[smason]

Re: Samsung 231T, recapped, no power, no lights

No voltage at the big cap should be easy to track down.
Is there AC at the input of the bridge rectifier? It's rare, but it could have an open diode.
I'd measure the AC right where it comes in to the board and trace it through 'till you lose it.

[PlainBill]

Re: Samsung 231T, recapped, no power, no lights

It's hard to tell because of the poor picture, but there seems to be TWO fuses in the AC input area. One is a black cylinder next to what appears to be the AC input connector, the other is a ceramic pigtail fuse above the two pin connector. As smason suggested, trace the circuit from the input connector to the bridge rectifier.

I've repeated this a number of times. When there are multiple boards, it really helps to have an over-all picture showing the boards in relationship to one another. Also, while including a large amount of the surrounding area isn't useful, it would be nice if I could see ALL of the boards.

PlainBill

[kingofcoins]

Re: More new pics

I've added some more pics to help clarify the board layout. It is inverter board on left, SMPS middle, and logic board right. Part of the trouble photographing and servicing this unit is because the connector header is soldered to join the SMPS and logic board together, and the ribbon cables are stuck on the logic.
I rechecked both fuses and they are about 2 ohms, The bridge rectifier has no shorts, and I get no AC voltage shown at the ceramic fuse.
Also the repair manual had no diagram for the Pwr Supply.
Thanks for the continued support.

[PlainBill]

Re: More new pics

I've added some more pics to help clarify the board layout. It is inverter board on left, SMPS middle, and logic board right. Part of the trouble photographing and servicing this unit is because the connector header is soldered to join the SMPS and logic board together, and the ribbon cables are stuck on the logic.
I rechecked both fuses and they are about 2 ohms, The bridge rectifier has no shorts, and I get no AC voltage shown at the ceramic fuse.
Also the repair manual had no diagram for the Pwr Supply.
Thanks for the continued support.

I'm curious about the two pin connector at the lower left corner of the SMPS board. This very much reminds me of the spot I'd put a power switch. If there isn't anything that plugs in there, a picture of the bottom of the power supply would be a big help.

PlainBill

[jetadm123]

Re: Samsung 231T, recapped, no power, no lights

A trivial detail, but is the AC outlet you're plugging into have power?

[kingofcoins]

Re: power on

Bill ...good eyes !.. yes that's for the external power switch on the RF shield, Sorry I had to remove to get the clear pics. It had a loose connection to board, but now its JB Bond tight...SO I get the green power on LED but no lights no sound.
I'll picking up a new multimeter this afternoon, so go ahead with any suggestions please.

I'm curious about the two pin connector at the lower left corner of the SMPS board. This very much reminds me of the spot I'd put a power switch. If there isn't anything that plugs in there, a picture of the bottom of the power supply would be a big help.

PlainBill

[retiredcaps]

Re: power on

SO I get the green power on LED but no lights no sound.

Hookup a computer so that it displays your favorite wallpaper. Can you see the screen if you shine a flashlight on it? When the lcd powers on, do the backlights flash at all?

[kingofcoins]

Re: green led only

Hi..thanks for stopping in retired....no I see nothing with or without flashlight, and no backlight flash, just green light only.
Should have new multimeter in an hour so go ahead...

[retiredcaps]

Re: green led only

no I see nothing with or without flashlight, and no backlight flash, just green light only.

Check the voltage regulators on the logic board. List the part numbers and measurements for IC101, IC102, IC105, and IC106. IC505 might be a voltage regulator, but I can't tell 100%.

I still think C111 and C102 look weird, but I have zero experience in poly caps.

[kingofcoins]

Re: green led only

Update using new multimeter...I have 14 and 5 volts out of P/S to logic board, ....but then 18VDC out of logic to inverter board, of course no voltage at lamps. How did voltage get stepped up?

Question on my re-cap job (see inverter pic)...I couldn't seem to get all the cap legs thru to bottom of board so some of these are more of a surface mount, however each leg hole in the board bottom is nicely closed with solder....is this a problem > Does solder always need to on top and bottom of PCB's ?

IC voltages IC 102... 1.25, 2.50, 5.0 VDC
IC 101, 105, and 106 all.. 0.0, 3.4. 5.0 VDC
IC505 is an Inverter..74F14,INVERTER,SOP,14P,150MIL,

[retiredcaps]

Re: Samsung 231T, recapped, no power, no lights

Tough to tell from the photos because they are a bit blurry, but it looks like there are 2 fuses on the inverter board. They are surrounded by the 4 caps.

[retiredcaps]

Re: green led only

Update using new multimeter

What brand and make multimeter did you get?