Samsung 933SN - 2sec on, then off

[teknoking]

Re: Samsung 933SN - 2sec on, then off

Thank you for your response. The top of the IC 802 is blown off! Looks like there are different versions of this power supply. I'll try the TOP256 and hopefully it should work. Will check the PCB first - trace tracks and make a little drawing to make sure I'm doing the right thing.

[redwire]

Re: Samsung 933SN - 2sec on, then off

LG W1941 service manual 2008 has some other power supply, it's not the W1941S service manual but label says it is.

OP has power supply IPLI-130 491861400100R
Your pic is power supply IPLI-114 491821400100R

U802 is a TOP Switch, but I can't read the full part number.
TOP25?PN. Guessing TOP256PN or higher power rating.

[teknoking]

Re: Samsung 933SN - 2sec on, then off

I know this is an old post but I have exactly the same power supply board on an LG Flatron W1941S. One of the chips is blown (IC802) and I cannot read the number. Can someone please tell me what the number is. Its probably a dual FET ic. I have downloaded a schematic which also does not make any sense as it does not tie up with what's on the PCB. Pin 3 is not used nor is there a pin 3 on the chip. Pins 5,6,7 and 8 are all joined together. See the attached pic of the board.

[rasika5054]

Re: Samsung 933SN - 2sec on, then off

pls tell me ic802 no of this board?

[rasika5054]

Re: Samsung 933SN - 2sec on, then off

i have board with burned ic 802 and i cant repair it ,because i have no ic802 no?

[rasika5054]

Re: Samsung 933SN - 2sec on, then off

pls tell me ic802 pno? thanks

[Lliro]

Re: Samsung 933SN - 2sec on, then off

Someone could tell me how to know identificate the resistor R823 on this power board?P

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Thanks Dragunov (and everyone else so far too) .. I'll get to testing tonight after work, or tomorrow.

[Dragunov]

Re: Samsung 933SN - 2sec on, then off

To check voltages you need to get 2 boards out of metal casing....

PUT PLASTIC/CARTON (NON CONDUCTIVE) COVER ON BACK OF DISPLAY... assemble boards on top of them and you can measure now....

like in my picture BUT WITH PLASTIC UNDER BOARDS! ... (this is a bit diferent but you will get the point).

[Dragunov]

Re: Samsung 933SN - 2sec on, then off

Try setting multimeter on the 2000 Ohm and test 2 pins on lamp transformer (connector side of transformer) if its shorted (0 or 0L) its bad... if not you should get reading about 1100-1400 TEST OFFLINE!

Try with another set of CCFL... Connect everything like it should but CCFL from another display... if lamps on other display are working its CCFL..........Try youtube to disassemble display... and if you are lucky you should get it working by resoldering CCFL.

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

I am unsure on how to check the voltages ..

For one, the board has to be flipped for me to check, and when it is flipped the CFL leads are too far away, and the LCD connector would be upside down.

http://i.imgur.com/LOcPjAt.jpg

[gurhy]

Re: Samsung 933SN - 2sec on, then off

7 out of 10 that circuit circled in red to the left is what's the cause of the issue

if you have not done so already try what nomoresonys has said "well, start by testing the connector on power supply for expected voltages, theres a label with expected voltages right by it, do you have a digital mutimeter?"


that will help diagnose the issue faster

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Thanks for the abbreviation info!

Well .. I was going to use my newly fixed Dell 173FPb PSU board to test the Sammy CFLs .. but now that board is experiencing the screen & LED slow 1 sec flash.

edit: well, now the 173FPb is on & working. It only started to flash after I 'woke up' my PC. After being unplugged for a few mins, its working now.

[momaka]

Re: Samsung 933SN - 2sec on, then off

Well .. I feel like a n00b .. I forgot to connect the PSU & controler/driver board.

Told you it happens more often than we like to admit is possible .

When ever there is a res change: GeForce BIOS Check, POST, starting Windows, Windows .. it does come back on for 2 seconds.

Yes, I think that is normal. Most monitors turn off the inverters when there is no signal (or momentarily turn it off before displaying a "No Signal" message).

This was the same issue I had with a Dell 173FPb. I replaced these transistors : 2SC5707 x4, FU9024N x2, and all is good. I did not see tiny transistors like those on the Samsung .. is it the larger thing on the mid-left, or the skinnier thing on the mid bottom? (sorry I don't know their proper names)

If you are talking about the inverter transformers (or in this case, your 933SN has only a single inverter transformer), it's the once circled with red on the mid-left in your picture, right above the board designator "T501". The other component you circled in red is a bridge rectifier.

Generally, you can tell what component is what by looking at the designators on the board. Anything that starts with a...
C --- capacitor
R --- resistor
L --- inductor
D --- diode
T --- transformer
F --- fuse
Q --- transistor (BJT, MOSFET, etc.)
IC --- integrated chip
FB --- ferrite bead (a small inductor)
J or JP - jumper

Here is what I suggest you do:
If you have another monitor that you know has good CCFLs, open that monitor and hook two of its CCFLs to the inverter of this monitor. See if that other monitor's CCFLs do the same 2-seconds-to-black when you turn on your Samsung 933SN. If yes, then the CCFLs in your 933SN are probably good too and likely there is something wrong with the inverter.

Seeing how much discoloration/darkening there is around the inverter transformer, though, I am leaning towards either bad inverter transformer or something wrong with that 8-pin DIP IC next to it (the 8-pin IC is likely what contains the transistors that drive the inverter transformer - i.e. similar to what the 2SC5707's do in the Dell 173FPb you mentioned).

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

~snip~
Now here is my question to you: Your title says: "2sec on, then off". What do you mean by "off"? Does the image on the monitor turn OFF *only* (with the LED on the monitor still indicating the monitor is ON).

~snip~
If it's issue #1 above, then you probably have an inverter problem (i.e. bad CCFLs/CCFL wires, bad inverter transformer(s), and/or possibly bad caps on the inverter rail)

This was the same issue I had with a Dell 173FPb. I replaced these transistors : 2SC5707 x4, FU9024N x2, and all is good. I did not see tiny transistors like those on the Samsung .. is it the larger thing on the mid-left, or the skinnier thing on the mid bottom? (sorry I don't know their proper names)

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Well .. I feel like a n00b .. I forgot to connect the PSU & controler/driver board.

It turns on now .. but I still have the same 2 sec on, then black, power LED is on. When ever there is a res change: GeForce BIOS Check, POST, starting Windows, Windows .. it does come back on for 2 seconds.

[momaka]

Re: Samsung 933SN - 2sec on, then off

Check the yellow fuse by the white connector that has the wires goes to the main board to see if it has DCV at each end of the fuse with ref to GND.

And if it's good, try removing it and see if the monitor will power up.

[budm]

Re: Samsung 933SN - 2sec on, then off

Check the yellow fuse by the white connector that has the wires goes to the main board to see if it has DCV at each end of the fuse with ref to GND.

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

check your soldering and that all the caps are in the right way around.

+1
Sounds like you either have a bad joint or a cap in backwards. -OR- you didn't forget to plug in that power connector to the logic board, did you now? (because, I have, even though I thought I double-checked everything).

By the way, I think you will like that HP w19b monitor. I fixed one a while back (random ceramic cap shorted on the t-con, so unlikely that you or anyone else will have this particular issue with that monitor). On mine, the TFT panel was made by Hannstar and had very good colors for an LCD - I'd say better than most LCDs.

I'll triple check each cap .. I am 99.999% sure I put them all in correctly.

And I'll double check the connectors on the board & to/from the side buttons connector.

The HP w19b seems to be a very nice vibrant monitor, but it's black has some ghosts/bleeding of the backlighting. It's not as uniform black as my Asus VH242H. I'll prolly be giving the HP to my sisters' kids, as they are using a HDTV for their monitor.

[momaka]

Re: Samsung 933SN - 2sec on, then off

check your soldering and that all the caps are in the right way around.

+1
Sounds like you either have a bad joint or a cap in backwards. -OR- you didn't forget to plug in that power connector to the logic board, did you now? (because, I have, even though I thought I double-checked everything).

By the way, I think you will like that HP w19b monitor. I fixed one a while back (random ceramic cap shorted on the t-con, so unlikely that you or anyone else will have this particular issue with that monitor). On mine, the TFT panel was made by Hannstar and had very good colors for an LCD - I'd say better than most LCDs.