Samsung 930b LCD cold start problem (inverter?)

[PlainBill]

Re: Samsung 930b LCD cold start problem (inverter?)

I wasn't using flash; however, my workbench light was pretty close. I've removed it and taken a top and bottom picture. The only place on the board where 13V is indicated is at the connector linking this board and the LCD's logic board. Tested it against ground (with everything hooked up).. 18.2V. Unfortunately, this is where my debugging knowledge stops (I know how to work a multimeter and soldering iron, but that's about it). I can't seem to locate a fuse, but I'm no expert at even identifying one, much less finding it on the board.

Thanks a lot for the quick reply and the advice so far =)

I'm understanding you to say 'No backlight', as opposed to 'two seconds of light, then no backlights.' If so, check F201. It appears to be mounted vertically between the caps and the heatsink.

PlainBill

[gypsy]

Re: Samsung 930b LCD cold start problem (inverter?)

I wasn't using flash; however, my workbench light was pretty close. I've removed it and taken a top and bottom picture. The only place on the board where 13V is indicated is at the connector linking this board and the LCD's logic board. Tested it against ground (with everything hooked up).. 18.2V. Unfortunately, this is where my debugging knowledge stops (I know how to work a multimeter and soldering iron, but that's about it). I can't seem to locate a fuse, but I'm no expert at even identifying one, much less finding it on the board.

Thanks a lot for the quick reply and the advice so far =)

[PlainBill]

Re: Samsung 930b LCD cold start problem (inverter?)

I have the same issue with my 930b; I opened it up and found the three 820uF 25V Samxons bulged. Everything else looked fine. I recapped all electrolytic caps I could find on the board save for the large 450V 100uF just to be sure (put 35V 1000uF instead of the 25V 820uF Samxons... is this OK?). The screen portion works (no-signal box moves around if I hold a flashlight to it) and the green light is on and solid. However, still no backlight. I've looked on the back of the PS board, and there appears to be this white powder around some resistors, with the board slightly browning around a transistor's heatsink solder blob. Pictures below:

1 2 3 4 5 6

What should I test/do to it next? Thanks =)

That white residue appears to be something left over from the manufacturing process. I doubt it's significant.

When taking pictures you get much better results if you turn off the flash, use a tripod, and take the picture by ambient light. That eliminates the glare.

The next step would be to check the 13V output of the power supply. If that is correct, pictures from directly above both the top (component) side and bottom (circuit) sides would be a big help. Also, look for a fuse in the area of the inverter (NOT the AC input fuse). If there is one, check that.

PlainBill

[gypsy]

Re: Samsung 930b LCD cold start problem (inverter?)

I have the same issue with my 930b; I opened it up and found the three 820uF 25V Samxons bulged. Everything else looked fine. I recapped all electrolytic caps I could find on the board save for the large 450V 100uF just to be sure (put 35V 1000uF instead of the 25V 820uF Samxons... is this OK?). The screen portion works (no-signal box moves around if I hold a flashlight to it) and the green light is on and solid. However, still no backlight. I've looked on the back of the PS board, and there appears to be this white powder around some resistors, with the board slightly browning around a transistor's heatsink solder blob. Pictures below:

1 2 3 4 5 6

What should I test/do to it next? Thanks =)

[EGuevarae]

Re: Samsung 930b LCD cold start problem (inverter?)

Partial Recap (replaced only the three bulged caps).


Complete Recap (note some of the 100uFs are slightly smaller now.



Original with my diagram to remember which ones went where

I normally replace C110 & C109 with 1000uf 16v. According to your notes on the picture, and by the size of the new installed ones, you replaced two 1000uf 10v caps with two 100uf 10v. That's a lot of difference (and that's why they are smaller). you see? a Pic told us something that you didn't.

[Krankshaft]

Re: Samsung 930b LCD cold start problem (inverter?)

The Samxon GF plague strikes again !

[Chaosratt]

Re: Samsung 930b LCD cold start problem (inverter?)

Partial Recap (replaced only the three bulged caps).


Complete Recap (note some of the 100uFs are slightly smaller now.



Original with my diagram to remember which ones went where

[EGuevarae]

Re: Samsung 930b LCD cold start problem (inverter?)

Well I'm now in possession of two of these with the same problem (got a steal on the second one, figured I could fix both and sell one for a profit).
Got the caps in from Digikey and recapped one PSU completely. Power it on and..... nothing. DSP/LCD still kick on (can see the faint "no signal" box with a flashlight), but there's a god-awefull squeal emanating from the PSU now.
Figure I fubar'd the recap (the 100uF's I couldn't match perfectly) I moved to the second PSU and recapped only the bad 820s using the Chemicon KY (exactly matching the OP's repair). Again same deal, everything except the CCFLs come on, and then it squeals. I've test both PSUs with both sets of CCFLs to the same result. These CCFLs also kick on fine when connected to a simple inverter used for aftermarket lighting kits.
Of note, I did NOT replace the large 100uF 470V cap, could this also be bad without showing any physical signs (and thus the stress of the load is shifted to it with the other bad Samxon's replaced?)

I'm realy at a loss here for what else might be bad, or what I may have done incorrectly.

Leave the big alone.
Post a pic of YOUR REPAIRED/RECAPPED BOARD (any of the two you just mentioned)

[Chaosratt]

Re: Samsung 930b LCD cold start problem (inverter?)

Well I'm now in possession of two of these with the same problem (got a steal on the second one, figured I could fix both and sell one for a profit).
Got the caps in from Digikey and recapped one PSU completely. Power it on and..... nothing. DSP/LCD still kick on (can see the faint "no signal" box with a flashlight), but there's a god-awefull squeal emanating from the PSU now.
Figure I fubar'd the recap (the 100uF's I couldn't match perfectly) I moved to the second PSU and recapped only the bad 820s using the Chemicon KY (exactly matching the OP's repair). Again same deal, everything except the CCFLs come on, and then it squeals. I've test both PSUs with both sets of CCFLs to the same result. These CCFLs also kick on fine when connected to a simple inverter used for aftermarket lighting kits.
Of note, I did NOT replace the large 100uF 470V cap, could this also be bad without showing any physical signs (and thus the stress of the load is shifted to it with the other bad Samxon's replaced?)

I'm realy at a loss here for what else might be bad, or what I may have done incorrectly.

[Chaosratt]

Re: Samsung 930b LCD cold start problem (inverter?)

So then, the thicker wire should be the main if possible, but for the -/+ 3 seconds its going to get plugged in it really doesn't matter?
Thanx, I'll see what I can do.

[PlainBill]

Re: Samsung 930b LCD cold start problem (inverter?)

$10 is well within my budget for repair. No fuses that I can see (or rather, nothing that looks to be like its a fuse). The bottom has almost no components, mostly just traces but I'll grab a pic of it tomorrow.

100 uF, 450 Volt is correct on the big cap.


My google searching leads me to believe that LCD inveters and CCFLs are basically the same, and interchangable with, the CCFLs kits used for lighting in computer cases.
Would it damage anything to get a cheap CCFL (Say off one of those lighted fan things) and wire it up to the inverter? That would give a quick indication of whether it was the inverter or the CCFL.
On that note, do CCFLs have a 'polarity'?

You have described a common test fixture. I often suggest buying one of the kits and using it to test both the CCFLs and the inverter.

CCFLs don't have a polarity in the usual sense. You will notice that one wire to the CCFLs has much thicker insulation. That wire always connects to the high voltage output of the inverter. The other wire is the return line, and goes to the circuit which senses the current through the CCFL.

PlainBill

[Chaosratt]

Re: Samsung 930b LCD cold start problem (inverter?)

$10 is well within my budget for repair. No fuses that I can see (or rather, nothing that looks to be like its a fuse). The bottom has almost no components, mostly just traces but I'll grab a pic of it tomorrow.

100 uF, 450 Volt is correct on the big cap.


My google searching leads me to believe that LCD inveters and CCFLs are basically the same, and interchangable with, the CCFLs kits used for lighting in computer cases.
Would it damage anything to get a cheap CCFL (Say off one of those lighted fan things) and wire it up to the inverter? That would give a quick indication of whether it was the inverter or the CCFL.
On that note, do CCFLs have a 'polarity'?

[PlainBill]

Re: Samsung 930b LCD cold start problem (inverter?)

OK, I don't know what this forum's policy is on thread necro but I'm going to bump this thread anyway. Found this via Google BTW.
I also have a Samsung 930B that suddenly decided that it didn't want to light. No fuss like the thread's OP monitor had, mine just didn't turn on one morning. Flashlight check showed the panel to be OK, just no backlight. I consider myself to be highly skilled when it comes to repairing minor problems and taking the LCD apart was no problem for me. However, diagnosing capacitors are a bit out of my area of experience. I note from the discussion above that you beleive the use of 15V caps may be a contributing factor in the inverter's demise. Mine uses 10v and 25V caps, but has a different PCB layout (though the components all seem to be the same, just moved/arranged slightly different).

My question is this, from looking at the pic below, am I looking at a bad inverter (dead caps) or is my problem the CCFLs? Looks like the green ones are bulged a bit, but I've seen that before on electronics that still worked perfectly fine. I'm fairly handy with a soldering iron, so replacing the caps will pose no problem to me.

My only question is how much money do you want to put into this? The caps are definitely garbage. They were junk when they came from the factory and haven't improved with age. Replace all of them (EXCEPT for the large one (100 uF, 450 Volt?) mounted on it's side). Replacing them with Panasonic FM or FC series should cost you about $10 from Digikey.

This may fix it, or it may not. Before you order the caps, check to see if there is a fuse to the inverter section. You might have shorted transistors or just a blown fuse. Good pictures of the bottom of the board would help.

PlainBill

[Chaosratt]

Re: Samsung 930b LCD cold start problem (inverter?)

OK, I don't know what this forum's policy is on thread necro but I'm going to bump this thread anyway. Found this via Google BTW.
I also have a Samsung 930B that suddenly decided that it didn't want to light. No fuss like the thread's OP monitor had, mine just didn't turn on one morning. Flashlight check showed the panel to be OK, just no backlight. I consider myself to be highly skilled when it comes to repairing minor problems and taking the LCD apart was no problem for me. However, diagnosing capacitors are a bit out of my area of experience. I note from the discussion above that you beleive the use of 15V caps may be a contributing factor in the inverter's demise. Mine uses 10v and 25V caps, but has a different PCB layout (though the components all seem to be the same, just moved/arranged slightly different).

My question is this, from looking at the pic below, am I looking at a bad inverter (dead caps) or is my problem the CCFLs? Looks like the green ones are bulged a bit, but I've seen that before on electronics that still worked perfectly fine. I'm fairly handy with a soldering iron, so replacing the caps will pose no problem to me.








For reference, here are the CCFLs:

[Wizard]

Re: Samsung 930b LCD cold start problem (inverter?)

Precisely.

If I KNOW the voltage on that buses then I can put 16V caps on 12V and 10V or 6.3V on 5V bus. If bus is greater than 16V and is around 22V max, 25V. If greater than that 22V, 35V so on.

Cheers, Wizard

[PlainBill]

Re: Samsung 930b LCD cold start problem (inverter?)

Just for the record ...

I asked myself "Why would they put two 15V and two 25V caps in a power supply like this one?" And the most logical answer is that it was an assembly error.

It is no cooincedence that I have a Samsung 930B with 'EXACTLY' the same problem and the same capacitor bulging. The photos could have been of my monitor.

The conclusion is this. Replace the two 15V 1000uf caps with 25V caps. All 4 should be of the higher rating. If you don't, you will be repairing the monitor again in a few months - for the same reason. The caps are being stressed above their design limits.

I can just imagine the assembly line, with people who have no clue how to read arabic numerals, stuffing circuit boards with 4 capacitors that look like, but are not alike. Did you notice that they are physically the same size? And easy mistake to make.

If you want the repair to be more reliable, don't just get better caps, get the ones that should have been placed there to begin with.

Good guess, but wrong. The problem is the original caps were garbage. I've only repaired a few LCD monitors, but I've seen the 'bulging cap' problem with 16V caps on a 5V line and 25V caps on a 12V line. Heck, I had one fail that was a 35V cap on a 12V line - and no sign of bulging.

PlainBill

[checkers1811]

Re: Samsung 930b LCD cold start problem (inverter?)

Just for the record ...

I asked myself "Why would they put two 15V and two 25V caps in a power supply like this one?" And the most logical answer is that it was an assembly error.

It is no cooincedence that I have a Samsung 930B with 'EXACTLY' the same problem and the same capacitor bulging. The photos could have been of my monitor.

The conclusion is this. Replace the two 15V 1000uf caps with 25V caps. All 4 should be of the higher rating. If you don't, you will be repairing the monitor again in a few months - for the same reason. The caps are being stressed above their design limits.

I can just imagine the assembly line, with people who have no clue how to read arabic numerals, stuffing circuit boards with 4 capacitors that look like, but are not alike. Did you notice that they are physically the same size? And easy mistake to make.

If you want the repair to be more reliable, don't just get better caps, get the ones that should have been placed there to begin with.

[Wizard]

Re: Samsung 930b LCD cold start problem (inverter?)

Actually, u need one that is made by reputable brand. Diamond was not one of these.

Back then, there were too many video card makers that doesn't program the eeprom with correct, vertified timings that follows the VESA specs. I seen this happen.

My advice: find matrox, ATi or sapphire (radeon series), nvidia reference-based video cards. I had similar complaints from customers with no video or out of range with LCDs and late CRT monitors and I knew it is the eeprom has incorrect video data set up issues.

Cheers, Wizard

[gdement]

Re: Samsung 930b LCD cold start problem (inverter?)

Probably, although I thought the old Diamond (pre-3D era, before they went bankrupt) was reputable.
Next time I'm using one of those cards I'll check the refresh rate on the monitor.

I had a more severe and obvious refresh defect with a Hercules Geforce2 MX card - it was over by about 5% in all modes. 90Hz in 85Hz mode, 64 in 60 mode, etc. This LCD didn't blank out on that card but it couldn't center the screen with it.

I wish I had some other really old PCI cards to test against. I'm curious if it's more an issue of age, like something tightened in the specs at some point. But maybe Diamond was just sloppy. Back when people had CRTs I guess it didn't matter much.

I do have an ancient 1MB ISA card, but I almost never have occasion to use that. Last time I used it, it actually had problems rendering the graphics in the BIOS POST SCREEN. I found that pretty hilarious.

[Wizard]

Re: Samsung 930b LCD cold start problem (inverter?)

Sounds like this video card is not programmed correctly for the text mode frequency. I had this problems with video cards that weren't reputable.

Replace them with reputable video cards like Radeon or different video card to try. Some LCD monitors have limited choices of frequencies especially down low also.

Cheers, Wizard