Samsung SyncMaster 2493HM - BN44-00195A - no power

[doorzon]

Hi all,

wondering if anyone has experience with the following problem.

I have a Samsung SyncMaster 2493HM here with the infamous BN44-00195A power supply board.
Been reading a lot of posts here on the forum about one or another issue with this power supply. In my case, the monitor is dead, the blue light does not turn on.

When the PCB has power, I get 0.25V on the 5.3V, no voltage on 24V. The voltage across the main cap is around 310V, which indicates an issue with the PFC circuit according to other posts in this forum?
All fuses are good, also the one on the logic board. But without 5.3V I suppose that does not even matter yet.

There are some schematics around for this board, but non of them are of the actual board when I compare the power input stage. Does anyone have an accurate schematic of this board? Or is the schematic from here sufficiently the same for troubleshooting?
https://www.badcaps.net/forum/attach...4&d=1344964111

From first impression I cannot see any parts burned, no caps are bulged. The board actually looks pretty good optically (I've seen a lot worse, as well in other posts here).
I still need to clean all the glue from the board, but it does not seem to be an issue, cannot see any burn marks even up close (see attached photos).
Does not mean any of them could not be broken.

Instead of shooting a cannon and replace all caps and some semiconductors and hope for the best, I'd like to understand and repair the parts that are broken.
Any nudge in the right direction would be appreciated.

[R_J]

Re: Samsung SyncMaster 2493HM - BN44-00195A - no power

The first voltage you need to have is the standby 5 volts, this can be checked between ground and DB851 cathode. If you do not have this standby voltage, check RB801s, and RB808 (the res. between pin 1 and hot ground) if either is open, icb801s is likely bad and the small electrolytics around it need to be replaced as well.

[doorzon]

Re: Samsung SyncMaster 2493HM - BN44-00195A - no power

Hi R_J,

thanks for the quick reply. After I did some measurements I decided to put the monitor back together partially. After this the power supply started to work again.
So it looks like there is a loose contact somewhere on the power PCB. Standby voltage is there as well as the 24V. Monitor now works as before.
If the problem comes back I'll pore some more time into this one. It's hard to find a fault if the damn thing is working ;-)

The high voltage transformers on the CFL PCB do make distinct a lot more noise (I'd say around 100-150Hz) but so far this is not a deal breaker.

Funny thing was, when I was measuring the voltage over a CFL power connection, even touching one pin of my multi-meter was sufficient to see some arching from this PCB island to my measuring pin. Did not expect that.
Perhaps the CFLs draw too much power or the yellow caps on this power converter are going bad. Will have to see how long this thing will hold.

Guess for now, this one is fixed!

thanks,
Doorzon

[R_J]

Re: Samsung SyncMaster 2493HM - BN44-00195A - no power

CFL means something else to me.
The transformers are switched at around 60khz~100khz If there is a poor connection it is likely on the components mounted to the heat sinks or the transformer pins, especially the ones with the rivets. If it happens again, re-solder those connections. You may want to re-solder the pins on the plugs like CN85, they don't look the best in the picture.

[doorzon]

Re: Samsung SyncMaster 2493HM - BN44-00195A - no power

Hi R_J,

thanks, will do. appreciate the assistance.

regards,
doorzon