Another SAMSUNG 2493HM !

[Leonrsa]

Re: Another SAMSUNG 2493HM !

I soften the glue with IP alcohol. 292V is on the low side, it should be close to 360~400VDC range, it sounds like the PFC Voltage booster circuit is not working. Your meter does not have capacitance measurement function? I would remove the cap then may take it to repair shop that may have cap meter to verify the value for you. If that cap is bad, you will not have 24V for running the inverter board, I assume that you do not have 24V at the inverter fuse?

Correct, I do not have 24V out. I will have the cap measured. And clean off all the glue.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

The cap was measured and checked out to be correct.
I am however worried as I am getting a reading of 294VDC across the big cap - the testing point there indicates that it should be 380V, with nothing but the AC cable connected. Am I correct in assuming the problem appears to be on the Hot side? Which components should I check out?
Ok, I connected all but the inverter board and measured 380V on the big cap, but still no 24V...
Where should I go from here?

[Behemot]

Re: Another SAMSUNG 2493HM !

Yes they are Hitano. Are those bad caps?

Yep and it does not seem you even have low-ESR caps. What series are they?

I soften the glue with IP alcohol. 292V is on the low side, it should be close to 360~400VDC range, it sounds like the PFC Voltage booster circuit is not working.

It is not with low output so if there is some preventing the main PSU turning on, the PFC boost is not active, rendering aprox. 315 V rectified. When the PSU turns on the boost turns on as well. Possibly low input voltage, in the range of 220 V AC?

[Leonrsa]

Re: Another SAMSUNG 2493HM !

I will try and obtain the correct low-ESR caps, and replace them all(again). Will report back whether the problem has been solved...

[Behemot]

Re: Another SAMSUNG 2493HM !

Have you also replaced the small capacitors? Usually you have to be very carefoul, sometimes changing low-ESR for GP and vice versa breaks the circuit operation. If you did, I can have a look at my board what caps are in each position.

[budm]

Re: Another SAMSUNG 2493HM !

Check the DC voltage on PS_ON pin on the power supply when you toggle the power switch, it should toggle between <1 and > 2V. hat is your AC line voltage feeding the unit? at 220VAC, the voltage on the main filter cap should be around 310VDC when monitor is OFF.
BTW, you have to have the monitor connected to running PC, otherwise it will go into standby mode in a few seconds if it does not see the video signal.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

Have you also replaced the small capacitors? Usually you have to be very carefoul, sometimes changing low-ESR for GP and vice versa breaks the circuit operation. If you did, I can have a look at my board what caps are in each position.

I did replace all the small caps about 3 moths ago, but it seems that the caps were GP Hitano. The salesman assured me that they were the correct type for the job...

I was under the impression that all the electrolytics had to be low-ESR?
This is the list I obtained of caps to be replaced:
Qty (2) 1000uf 35v
Qty (1) 2200uf 10v
Qty (1) 470uf 35v
Qty (1) 1000uf 10v
Qty (2) 10uf 50v
Qty (1) 2.2uf 50v
Qty (3) 47uf 50v
Qty (1) 22uf 50v
I will try and find caps of the make as listed on this thread:
https://www.badcaps.net/forum/showthread.php?t=2280
thanks for the help so far

[budm]

Re: Another SAMSUNG 2493HM !

So what DC voltage do you have at PSON pin?

[Leonrsa]

Re: Another SAMSUNG 2493HM !

Hi budm, I am afraid I did not measure the voltage on PSON as I have put the monitor aside until new caps arrive. I was informed that the caps I used (Hitano) as replacements 3 months ago were bad and not ESR. I have ordered the best (in South Africa) low-ESR caps I could find, being Rubycon YXF series, and will report back on progress.

[Behemot]

Re: Another SAMSUNG 2493HM !

I got first sucessfull pacient, this tiem only caps were bloated. Still got two with blown primary, unable to bring them back to life

[Leonrsa]

Re: Another SAMSUNG 2493HM !

PSON, Off - 0.12V, On - 3,2V
Replaced caps, still no image. Blue light comes on. Can someone please suggest the way forward?

[budm]

Re: Another SAMSUNG 2493HM !

You have PS_ON bu the PFC Voltage booster is still not working, PFC circuit section will need to troubleshoot next.

[Behemot]

Re: Another SAMSUNG 2493HM !

Budm you sure? The booster is off when only SB supply runs, with aprox. 315 V DC rectified.

[budm]

Re: Another SAMSUNG 2493HM !

In standby mode with 220VAC input, the VDC on the filter cap is about 220VAC X 1.414 = 311VDC. When PS_ON is applied, the PFC Voltage booster will kick in to boot the voltage to about 360~400VDC range. He indicated that he has 292VDC on the cap which lower than it should be unless his line voltage is <220VAC.

[Behemot]

Re: Another SAMSUNG 2493HM !

What else than some undervoltage may that be? Where else would the power go when the boost is not active? It would have to be burned somewhere, he did not indicated somethig is heating in it…

[budm]

Re: Another SAMSUNG 2493HM !

The only load it has is the standby power supply. He needs to find out first what is his AC voltage is, if it is 220VAC, then next place to check will be that main filter cap, check it capacitance and the AC ripple on it.

[Behemot]

Re: Another SAMSUNG 2493HM !

Oh yeah, good point with the capacitance, non-true RMS voltmeters won't read amplitude

[budm]

Re: Another SAMSUNG 2493HM !

I use FLUKE with T.R.M.S.

[Behemot]

Re: Another SAMSUNG 2493HM !

On the other hand it won't tell you capacitor may be bad if you don't have ESR meter…while El Cheapo meter would at least indicate.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

In standby mode with 220VAC input, the VDC on the filter cap is about 220VAC X 1.414 = 311VDC. When PS_ON is applied, the PFC Voltage booster will kick in to boot the voltage to about 360~400VDC range. He indicated that he has 292VDC on the cap which lower than it should be unless his line voltage is <220VAC.

I found the following...
Line voltage - 205VAC
450V Cap - Standby - 290VDC
- On - 390VDC
Seems to be OK