Another SAMSUNG 2493HM !

[budm]

Re: Another SAMSUNG 2493HM !

Vcc at the IC pin is 12.48VDC?
Per post 23:
"C) checked the operation of the MC33067P ICM801
pin 14 was always high and pin 12 alway low...check the oscillator (pin 2 ) and their was no oscillations there, so I started looking at reasons for not startup of the IC in the datasheet...
pin15 12V was ok (power supply)"
If I rememember corectly, it should be around 15VDC.
By the way, which schematic diagram you are using?
The diagram of the 192A is real close to 195A, only the designators are not the same, but the connections wise are the same.

[Behemot]

Re: Another SAMSUNG 2493HM !

I looked into datasheet of the MC33067P and it says 20 V, but reading it carefoully reveals it is *maximum* ratings

I more like read old threads because what I have found, there is only diagram for another version of this board and it seems there are some differences.

As for the oscillation, is it safe to just wire o-scope to that? McEugene had double separation transformer for that. All I have at my disposal is 2kVA mains separation transformer.

[budm]

Re: Another SAMSUNG 2493HM !

The board you are working on should be connected to the Isolation transformer so the primary side of the primary side will be floated. The scope can then be connected directly to the AC outlet.

[Behemot]

Re: Another SAMSUNG 2493HM !

Pin 12 (drive output B) is high (11,5 V or so), pin 14 (drive output A) is low (under 0,3 V). Pin 10 is 0 V.

Here are shots from pin 2 (osc) and pin 10 (fault).

I think the driver is working fine, isn't it? Unfortunatelly I cannot directly connect my scope to the SMPS transformer primary as it is CAT I/300 V max. But if the driver circuit is OK and transistors are being driven, than I think there is only one conclusion - transformer winding is shorted.

[Behemot]

Re: Another SAMSUNG 2493HM !

OK those images are useless, I know These are DC coupling from pin 14, the same is on pin 12 just on lower potential. So far this is OK I think, right? Saw tooth wave, that seems OK to me. It goes well all the way to resonant transformer primary legs.

On the other side of resonant transformer, I got this output on the second image. Not sure, should it be driven this way? I find it somewhat difficult to drive 500V MOSFET with 50 mV pulses, right??

[Behemot]

Re: Another SAMSUNG 2493HM !

I am taking appart that old HP P1130 CRT which died and besides all the huge semiconductor, nice caps and lot of non-ferrous metals I found this tunable 1:1 transformer (it has worm core which you can move left and right) so I think I can make sepparation transforer out if of to measure primary of the transformer directly, whaddaya think? I can set it the way basically the whole core is on one side.

[Behemot]

Re: Another SAMSUNG 2493HM !

Do you think it's worth a shot? I don't want to blast my new O-scope off…

[the_raver514]

Re: Another SAMSUNG 2493HM !

hi.

i had this exact model of monitor to repair for a Customer. you know what... the problem was exactly that same resistor... color code is red red silver gold wich is 0.22 ohm, did the replacement and yes it did revive the monitor! always keep faith even when youre desperate...

[the_raver514]

Re: Another SAMSUNG 2493HM !

lol sorry wrong thread

[Leonrsa]

Re: Another SAMSUNG 2493HM !

Hi, I am new to the forum so forgive (or reprimand) me if I am out of line!
I have the same dark screen but an image is visible via the torch test. I will be replacing the 2 470uF caps on the inverter board and report back. The caps on the power supply board has been replaced 3 months ago, but the problem came back...

[Behemot]

Re: Another SAMSUNG 2493HM !

Clean that bloody glue on the power board immediatelly otherwise over time you will only add to the number of people with blown power supply unable to fix it. After that replace all the bad-brand caps (not only the ones obviously bad) with quality ones.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

I replaced the 2 caps and cleaned off the glue. The monitor now seems to be completely dead. No image using the torch test, and obviously no backlighting. Only the glowing blue light...

[Behemot]

Re: Another SAMSUNG 2493HM !

Is the polarity OK?

[budm]

Re: Another SAMSUNG 2493HM !

@leonrsa: post pictures of your boards please.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

I hope these are clear enough.

[Behemot]

Re: Another SAMSUNG 2493HM !

Looks to me like (s)Hitano caps.

[budm]

Re: Another SAMSUNG 2493HM !

Check the capacitance of that rectangular blue cap (CM812). You still have quite a bit of glue on the components, especially the dark brown glue one (some of the glue did not turn dark brown yet).
This will happen when glue gets worst:
https://www.badcaps.net/forum/showthread.php?t=34692

[Leonrsa]

Re: Another SAMSUNG 2493HM !

Looks to me like (s)Hitano caps.

Yes they are Hitano. Are those bad caps?

A search of the list of bad caps on this forum for Hitano came up blank...
It did come up on the good caps list though.

[Leonrsa]

Re: Another SAMSUNG 2493HM !

Check the capacitance of that rectangular blue cap (CM812). You still have quite a bit of glue on the components, especially the dark brown glue one (some of the glue did not turn dark brown yet).
This will happen when glue gets worst:
https://www.badcaps.net/forum/showthread.php?t=34692

Hi budm, quite difficult to scrape the glue off! Is there a way to soften or perhaps dissolve it?
I have no way of measuring capacitance, should I replace the cap(CM812)?
Incidently, the voltage on the big 450WV82uF cap is 292Volts. Is that within spec?

[budm]

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?