Samsung 930b LCD cold start problem (inverter?)

[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.

[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 =)

[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 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 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?)

Correct, I get absolutely no backlight whatsoever. I found an F301 at the location you specified; it's shot. I attached a picture of it, looks to be 3A, not sure what the symbol beside it is. What should I ask for when I hit up the parts store tomorrow?

[PlainBill]

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

Correct, I get absolutely no backlight whatsoever. I found an F301 at the location you specified; it's shot. I attached a picture of it, looks to be 3A, not sure what the symbol beside it is. What should I ask for when I hit up the parts store tomorrow?

That may be a manufacturer's logo. I'd ask for two 3A 125 Volt fast blow Picofuses. Just to improve your odds of using only one of them, check U202 and 203. Make sure they are not shorted. Also compare the resistances of the primary and secondary windings of T301 and T302

PlainBill

[gypsy]

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

I've checked the resistance on T301 and 302, it's identical. In terms of U202 and 203, they seem to be two ICs; Google search got me: Low-Voltage, SPST, CMOS Analog Switches. I've looked at the datasheet and tested continuity between all pins that are connected (save for ground), nothing - if I understand this correctly, they should be fine.

I'll hit up the parts store first thing tomorrow morning and let you know what happens. Thanks for all the help so far =)

[gypsy]

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

That fixed it! Bright as daylight and stable too. I reclaimed a $250 piece of hardware, thank you so much for the detailed advice and taking the time to look at my board =)

[PlainBill]

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

That fixed it! Bright as daylight and stable too. I reclaimed a $250 piece of hardware, thank you so much for the detailed advice and taking the time to look at my board =)

Hey, don't sell yourself short. You did the hard work!!!

PlainBill

[bellevue28]

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

That may be a manufacturer's logo. I'd ask for two 3A 125 Volt fast blow Picofuses. Just to improve your odds of using only one of them, check U202 and 203. Make sure they are not shorted. Also compare the resistances of the primary and secondary windings of T301 and T302

PlainBill

I see the U202 and 203 ... how would i test those?
Continunity? There's 8 leads....




Hello
Very new to all of this but i see too many of these monitors go bad and trying my hand at some of this. This one is was given to me by a friend who just moved on to a newer model, so I am trying to score a free monitor.

I got to the blown F301 also.
This board has a TON of the white putty all over these parts. trying to cut some off to be able to replace this fuse.

The underside of this board is a little browned in the D106 and D107 area, If the issue is just heat, this putty can't be helping.

(on an unrelated note, My other samsung (205bw) works only when an exhaust fan is over it, and hasn't blinked since.)

[PlainBill]

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

I see the U202 and 203 ... how would i test those?
Continunity? There's 8 leads....

Look up the part number, get the data sheet.. There are two types used. One has one pin for for the gate, three pins are tied either to the source or the drain, the remaining pins are tied to either drain or source. On an ohms scale drain, source, and gate should be open to one another. If the part is a dual or complementary package, do the same thing.

Hello
Very new to all of this but i see too many of these monitors go bad and trying my hand at some of this. This one is was given to me by a friend who just moved on to a newer model, so I am trying to score a free monitor.

I got to the blown F301 also.
This board has a TON of the white putty all over these parts. trying to cut some off to be able to replace this fuse.

The underside of this board is a little browned in the D106 and D107 area, If the issue is just heat, this putty can't be helping.

(on an unrelated note, My other samsung (205bw) works only when an exhaust fan is over it, and hasn't blinked since.)

How do the caps look? Common issues on monitors are cheap caps failing because they're cheap crap and bad solder joints. If any cap is bulging, replace them all.

Also, most people here don't have all monitors available for reference. And quite often two monitors with the same model number will be different internally. Posting good pictures improves chances of getting good advice.

PlainBill

[bellevue28]

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

Hi Bill ..
Been reading a bit on the history of this site ... nice place you have.

So 3 larger caps in series are slightly bulged, the green board underneath is slightly browned so it seems to be time for new caps on these.

Pics to follow tomorrow but thanks for the reply ...
I think I will be placing an order soon

time to find the exacto knife, somebody went crazy w/ the caulk gun on this thing.

[PlainBill]

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

Hi Bill ..
Been reading a bit on the history of this site ... nice place you have.

So 3 larger caps in series are slightly bulged, the green board underneath is slightly browned so it seems to be time for new caps on these.

Pics to follow tomorrow but thanks for the reply ...
I think I will be placing an order soon

time to find the exacto knife, somebody went crazy w/ the caulk gun on this thing.

I've no part of the ownership of this site. The guy who does runs it a lot better than I ever could (except for the 10 minute limits on editing posts)

If you look over the white goo, that's part of the production process (I worked in electronics production for 10 years). When boards go over the wave solder machine some components tend to lift up or move around. The glue holds them in place so they don't have to be repositioned by hand afterward. (The wave solder operation at CPRD had two or three guys running the wave solder equipment and trimming the leads. And touch-up had 4 people repositioning components and 2 installing parts that couldn't be wave soldered.)

PlainBill

[EGuevarae]

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

I've no part of the ownership of this site. The guy who does runs it a lot better than I ever could (except for the 10 minute limits on editing posts)
.....
PlainBill

[zeal]

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

My 930b just went black last night. I've already ordered a a new display but I'm still going to try to fix the samsung. I've had this display for 5+ years so I've definitely got moneys worth. Theres a lot of good info in this thread already so I'm not asking for help....yet.

Also....I'm finding it slightly ironic that at the top of this page there is a Samxon capacitor advertisement...

[EGuevarae]

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

Also....I'm finding it slightly ironic that at the top of this page there is a Samxon capacitor advertisement...

Not all Samxon are crap. GF series are the most problematic in the conditions they are normally used (no vent, heat...)

[PlainBill]

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

My 930b just went black last night. I've already ordered a a new display but I'm still going to try to fix the samsung. I've had this display for 5+ years so I've definitely got moneys worth. Theres a lot of good info in this thread already so I'm not asking for help....yet.

Also....I'm finding it slightly ironic that at the top of this page there is a Samxon capacitor advertisement...

Take a look at the list of bad caps.

PlainBill

[tiloup]

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

Hi from Guadeloupe everybody !

Thanks a lot for your forum, it helped me because I have exactly the same problem with my Samsung 930BF : one 1000 µf 16V cap was bulging.
As it is very difficult here in Guadeloupe to find parts, I commanded the repair kit to CCL-LA : never received the caps since two months....
The only cap I found is a second hand 1000 µf 35V / 85 C°, and I don't know if it is really low ESR.
So I soldered it yesterday : now screen is not dark, it is completly white, the power led is not blinking, but no picture at all, as here (thanks to Gdement for the picture) : https://www.badcaps.net/forum/attach...achmentid=8267
Any idea ?
Thanks in advance, and have a nice day !
Phil 'Tiloup'

[PlainBill]

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

Hi from Guadeloupe everybody !

Thanks a lot for your forum, it helped me because I have exactly the same problem with my Samsung 930BF : one 1000 µf 16V cap was bulging.
As it is very difficult here in Guadeloupe to find parts, I commanded the repair kit to CCL-LA : never received the caps since two months....
The only cap I found is a second hand 1000 µf 35V / 85 C°, and I don't know if it is really low ESR.
So I soldered it yesterday : now screen is not dark, it is completly white, the power led is not blinking, but no picture at all, as here (thanks to Gdement for the picture) : https://www.badcaps.net/forum/attach...achmentid=8267
Any idea ?
Thanks in advance, and have a nice day !
Phil 'Tiloup'

The 'all white' screen can have several causes. The simplest is a loose cable from the logic card to the panel itself. The next is an open fuse on the panel card (often hidden behind a metal cover on the LCD panel. Another possibility is a problem with the power supply on the panel card.

PlainBill