Samsung 2493HM Power Board failure

[edenexter]

Hi everyone,

this is the second time my Samsung 2493HM broke down. The first time a bunch of caps clearly failed. I believe I only replaced the blown caps (not all... stupid), but that did the trick.

A few days ago the monitor went out with some sparks coming out the back and tripping the fuse box in my house. I decided to open up the monitor before trying to turn it on again in fear of more parts failing.

Looking at the PSU board I see that:
- CM855, a 470uF cap, has failed (probably didn't replace this one the first time).
- RM801, a 0.22R resistor, was the resister that failed and caused the sparks.
- QM802, a FQPF9N50C MOSFET, looks like it failed and burnt, but that could be from the failing resistor sparks.
- On the back it looks like RT852, a 100R smd resistor, has failed.

I've seen two schematics going around on the site but neither seem to be exactly the BN44-00195A board scheme. Anyone got the right one?

My question right now is where should I go from here.
- Reading other threads it looks like I should swap out the QM802 and QM803 MOSFETs.
- I read that RM801 is a fusible resistor. Are these different from 0.22ohm 1w resistors? Or should it be 1/2W.
- I'm considering recapping the whole board again with better quality caps.
- The 100R smd resistor and the transistor and zener to the right of it are likely to have all failed and need replacing.

Other than this can anyone recommend some other steps for me to take to ensure this goes right? I've got a multimeter, perhaps I should measure some things, but this is hard without the proper schematic.

note:
- I took some pictures, but I had already removed QM802 and RM801.
- I've done my best to get rid of the adhesive, but it's quite hard to remove.
- The fuses on the board haven't failed.
- The inverter board looks good to me, but I'll replace the caps on this one as well.

Thanks!

[gabi314]

Re: Samsung 2493HM Power Board failure

I have same resistor RM801 that failed.
Did you fixed it?

[Rtech]

Re: Samsung 2493HM Power Board failure

the usual cause is the Q802 Mosfet going Short cct.It is unlikely that the original poster will see your question,and Posters regularly fail to advise what results they do get in the end,which is a pity,but in this case, i would suggest the faults he found would have been the problem,and replacing the parts would have probably returned his monitor to a working condition.

[Pauldesign]

Re: Samsung 2493HM Power Board failure

The possible failed component(s) will be the following;

- The MOSFET as indicated -- any equivalent should work, double check both datasheets -- check for shorts
- The short circuit or current sense resistors -- usually less than an Ohm (0.2 to 0.4 ohm) -- check for open
- The PWM chip; check for shorts across pins
- Finally, surrounding resistors linking those components -- check for opens.