Samsung 2493HM - Blinking Power LED Problem

[SoDown]

Let me start off by saying that i know that there already exits a thread with a name similar to this one, but the guy in that thread didn't reply if it was fixed or not, so i'm starting a new one, feel free to merge them if necessary.
With that out of the way, my board models are:

Power Supply: BN44-00195A
Main board: BN41-00962A

What did i do:
I replaced 2 resistors RM801 0.22 and RX801S 750K using schematics i downloaded, removed almost all of the brown glue on high voltage parts, checked voltage on Power_EN which was 0~0.3, and S_B which is 5.2~5.3V, 0V on 24V, and 0V on 18V lines. (See attachments below)
Problem is, once i connect Main Board i start hearing high pitched whining somewhere on the Power Supply Board, and it's in sync with the LED blinking. Any guidance on where i should measure and what i should replace is very much welcomed. Thanks.

[CapLeaker]

Re: Samsung 2493HM - Blinking Power LED Problem

do you get any PSon from the main board, when you try to turn the monitor on??

[R_J]

Re: Samsung 2493HM - Blinking Power LED Problem

If RM801 was open, there was/is a problem with that part of the supply, Check QM801 and QM802, I suspect you could also have a shorted secondary diode for the 13 or 24 volt supplies.
The high pitched whinning usually means the primary side is trying to operate but there is a short somewhere in the secondary. This high load could be on the main board orit could be a fault on the inverter board killing the 24 volts, disconnect the plug going to the inverter and see if the voltages come up.
You can disconnect the main board and connect a 500Ω~1K resistor between standby 5.2v and POWER ON_OFF and see if you get the 13 & 24 volts

I don't see why you replaced RX801S was it open? It will not effect the operation of the power supply.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

do you get any PSon from the main board, when you try to turn the monitor on??

Nope, i get some small voltage on PS_ON (0.3-0.01 keeps changing) on it.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

If RM801 was open, there was/is a problem with that part of the supply, Check QM801 and QM802, I suspect you could also have a shorted secondary diode for the 13 or 24 volt supplies.
The high pitched whinning usually means the primary side is trying to operate but there is a short somewhere in the secondary. This high load could be on the main board orit could be a fault on the inverter board killing the 24 volts, disconnect the plug going to the inverter and see if the voltages come up.
You can disconnect the main board and connect a 500Ω~1K resistor between standby 5.2v and POWER ON_OFF and see if you get the 13 & 24 volts

I don't see why you replaced RX801S was it open? It will not effect the operation of the power supply.

Checked QM802(QM801 on scheme), desoldered it, measured it using multimeter as i don't have any proper equipment, and it looks fine, as for QM803(QM802), i couldn't desoldered it as it was in a tight spot, maybe i'll try it later again. What i did do is clean some more brown glue on TM801(TM802) and the cap near it. As for the Inverter, i didn't connect it, i just measured the voltage on the Power Supply Board connector and so far it's 0V.
Also i replaced RX801S because it smelled like it was burnt, and once i took it out and measured it it didn't display correct resistance, that's why i replaced it.

[Dumah Brazorf]

Re: Samsung 2493HM - Blinking Power LED Problem

In cases like this is useful a bench power supply in order to inject power on the rails and see if there is a short and also test the feedback circuitry (tl431 and optocouplers)

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

In cases like this is useful a bench power supply in order to inject power on the rails and see if there is a short and also test the feedback circuitry (tl431 and optocouplers)

Unfortunately i don't have a bench power supply, maybe i can hook some 5V(or lower) charger that i have laying around? Also i ordered a cheap component tester, so i plan on taking capacitors and resistors/diodes/etc off and testing them one by one.

[R_J]

Re: Samsung 2493HM - Blinking Power LED Problem

Try turning on the power supply board by itself (no main or inverter connected) that will tell you if the power supply is working

[CapLeaker]

Re: Samsung 2493HM - Blinking Power LED Problem

Yep, I agree... force the PSU on without any other boards connected to it.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

Did just that, forced it on with a 1k Ohm resistor, and i still got no voltage on 24/18/5.3V ones, what i did find out tho is that 2 diodes near ICM801 are shorted and so is one SMD capacitor near the IC, also, i tested between VCC and GND of the IC and got near 0 (Watched some YT video where a guy said to test it, and if it's near 0 then it's dead). So what i'll be doing is ordering a new IC(MC33067P) which will take a while to get to me and in the mean time testing all of the transistors/diodes/etc. The picture below shows about the shorts, also, if i'm wrong somewhere, please correct me, thanks.

[R_J]

Re: Samsung 2493HM - Blinking Power LED Problem

I think this schematic is very close (the location numbers may not match) For example, the two diodes marked on YOUR board are DM801 & DM802 in this schematic.
I would remove one end of the diodes and recheck them. It is possible the ic could be ok.

[budm]

Re: Samsung 2493HM - Blinking Power LED Problem

After replacing the bad parts, make sure to check that blue rectangular cap (12n J printed on top) to make sure its capacitance is still good, that is one common failure cap for 24V power supply section.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

Ok, some updates. I removed the 2 diodes in question(DM801/DM802), and the 1 SMD cap(Pin 12), tested them with the ESR tester, and they're fine, i think(pic below). I also took some time to remove the QM802 and QM803, tested them and they also look fine, removed the CM808 Cap, and the TM801(one side, pic below) as well.Now, since i removed the 2 diodes and the rest i tested for shorts, and i'll mark them in the pic below. Correct me if i did something wrong, thanks.

Edit: What i meant with "1 Probe here" is that i'm keeping 1 probe on that spot and touching the other same colored spots with the other probe.

[CapLeaker]

Re: Samsung 2493HM - Blinking Power LED Problem

so you got a short across that cap? first pick, smack in the middle?

[R_J]

Re: Samsung 2493HM - Blinking Power LED Problem

I would guess the ic's internal outputs are shorted based on his RED dots. I hope he is NOT relying on the BEEP of his meter to determine a short.

[CapLeaker]

Re: Samsung 2493HM - Blinking Power LED Problem

...or he didn't let the cap charge up. But if there is a dead short on the cap, something is fishy and it should be easy to find.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

Sorry for long period of silence, i was waiting for the IC(MC33067) to arrive from China. Once it did, i replaced the old one, connected everything together and solved the old problem, which was blinking Power LED, now it doesn't blink anymore. But now a new problem, once i try to power it on, the backlight starts flickering like crazy, i measured 21V on the 24V line to the inverted, didn't measure rest of the voltages yet, will do that later and update this post with them.

I also compared the old IC with the new one, and the new one atleast has some internal resistance, unlike the old one which is just dead short.

Also for Budm, i checked that blue cap and it measured 11.66nF.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

Sorry for long period of silence, i was waiting for the IC(MC33067) to arrive from China. Once it did, i replaced the old one, connected everything together and solved the old problem, which was blinking Power LED, now it doesn't blink anymore. But now a new problem, once i try to power it on, the backlight starts flickering like crazy, i measured 21V on the 24V line to the inverted, didn't measure rest of the voltages yet, will do that later and update this post with them.

I also compared the old IC with the new one, and the new one atleast has some internal resistance, unlike the old one which is just dead short.

Also for Budm, i checked that blue cap and it measured 11.66nF.

Did some measuring, and here's the results: PS_ON is 3.2V, S_B is 5.24, 5.3V line is present with 5.4V on it, 24V line is present sometimes with 21V on it, i also hear some crackling while it's on, i previously didn't hear that. Any clues on what might crackling, also any clues as to why i'm not getting 21V on the 24V line ? Thanks.

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

Forgot to mention that i'm getting a picture on the screen, but the backlight keeps flickering, so the problem is either in the inverter itself or maybe the power supply board. I have no way to test the CCFL's, so can't really tell if it's them.As for the inverter, i'll try to get my hands on a <14W CFL lamp and test it like that(I have a 30W one now). Also, anyone got a schematic for the inverter board(BN44-00136B)? Would help me a lot knowing where what is connected, thanks . Pics of the inverter board included below

[SoDown]

Re: Samsung 2493HM - Blinking Power LED Problem

MONITOR FIXED

The monitor is finally fixed, what was the cause of the 21V on 24V line problem was the transformer that's driving the 2 main MOSFETS, it had a broken pin(pic below), i bodged it, cleaned the board a bit, and it worked like new. So again, from start to finish to what was wrong, the standby power LED was blinking, i wasn't getting any voltages at all(5.4V/21V), i tested the VCC and GND of the MC33067 IC, and they where shorted, replaced it, and got my standby power LED fixed, i got almost all the voltages, except the 24V line which was 21V. To fix that i just rechecked the TM802(Transformer), in my case the reason the pad was ripped was because of me overheating the area. What caused all of this is probably the brown glue that was on the transformer, that shorted it thus killing the IC.

Also, to mods, please add to this thread [Solved] or something similar, thanks.