samsung syncmaster 2233

[george79]

Hello again
trying to repair a Samsung monitor 2233
monitor turn on, start a picture for 2 secs and then turn off, the same as troubles with the CCFL lights.
tested the lights on the back of the screen and they are working, but one output on the power supply is dead.
i tried to fix it, but there is no schematic
as you can see on the photos, in the center between the 2 electrolytic capacitors and the heatsink, there is a black spot. Under this black spot on the PCB there are two capacitors and some diodes and transistors, i suspect somewhere there the problem. Because all electrolytic changed without success.
Can i find somewhere a schematic of the power supply? any info please???

Thank you for your time
George

[TheMG]

When you say one output is not working, do you mean one of the low voltage outputs of the power supply? Or one of the high voltage CCFL driver outputs?

[george79]

sorry, one of the HV output, when you swap the tubes they light, so one output from the board is defect

[TheMG]

In that case the problem is somewhere on the secondary (output) side of the HV transformer, since the same transformer supplies all the lamps.

Could be a bad transformer secondary winding, open-circuit somewhere, or a bad HV ceramic capacitor. Not much to it really, the two lamps that run off the same secondary winding are effectively in series, with the center connection running through some resistors for current sensing. By the looks of it, this circuit also uses a capacitive divider for voltage sensing.

[alligatorblues]

I've converted a number of Samsung ccfl monitors to LED backlight. Then you just disconnect the HV altogether, and run the LED board off the 12 V DC on the connector from the PSU to the logic board. You have to take the display apart to put the LED strips in. But you get a brighter monitor that consumes 1/2 the power.

I still have some light strips and boards. Brightness, contrast, and everything else works too. Theres a total of 4 wires to splice into the above mentioned wire bundle, and the PSU should have labels for what each wire is. Presently, I'm using 3 21" monitors that all failed and were converted. One of them is coming up on 8 years since the repair, and it is still bright as heck.

Depending on how wide your monitor is, that solution would work great. PM me if you need the LED strips and regulator board. The whole job takes about 2 hours for a first-timer.

[george79]

OK, desoldered the HV transformer
primary side is 0,08 ohm
secodaries are, 0,9Kohn and 5,7Kohm!!

will try a second one i have from spare monitor and see what we have, thanks for the replies
By the way, if you have a schematic for this board, or a close enough on the secondary HV side, to see how its working, can you post it here???

Thank you
George

[TheMG]

Both secondaries should have practically the same resistance, so this is indicative of a bad transformer.