Samsung SyncMaster 2493HM black screen

[gr8leap]

My issue's with this monitor began shortly after a storm. The screen went black and the blue power light flickered a moment than went steady blue. There was a burning smell so I am assuming something was blown up!

While checking for blown capacitors I found a burn. Not sure exactly what it is. Hoping that you guys can help.

Thank you

[budm]

Re: Samsung SyncMaster 2493HM black screen

To start with, you need to remove ALL those glues, they are corrosive and conductive. Use denatured alcohol to soften them first. Then we can see what damages it has on the board.
Read this link: https://www.badcaps.net/forum/showth...t=22008&page=2

[euromatlox]

Re: Samsung SyncMaster 2493HM black screen

That power board seems to be BN44-00195A. Easiest fix is to buy (or find) somewhere BN44-00173A power board and use it instead.

BN44-00173A is usually very easy to fix if it fails (replace some resistors and capacitors). In the worst case BN44-00195A might require some SMD component soldering and it might fail again easily (or something was missed during repair).

About other Samsung models, 245B has BN44-00173A, 245B+ has BN44-00195A.

You can google more using the board codes, to find earlier discussions here about the matter.

[ben7]

Re: Samsung SyncMaster 2493HM black screen

Looks like either a part under that glue has burnt out, or a mosfet has gone short and burnt up the GDT (gate drive transformer).

[gr8leap]

Re: Samsung SyncMaster 2493HM black screen

@budm - I did as you suggested and removed as much of the glue as I could. That stuff is baked on there though

@euromatlox - Thats what i am thinking. I'll take the easy way out and source a new psu.

Was this most likely caused by the glue becoming conductive? There was a brief power outage due to a storm. The monitor worked fine the rest of the night with no issues. The following morning I turned it on and solid blue power light.

Thanks again for the help and suggestions!

[budm]

Re: Samsung SyncMaster 2493HM black screen

Here is some info.
I have seen the problem since the 70's.

[lexwalker]

Re: Samsung SyncMaster 2493HM black screen

My issue's with this monitor began shortly after a storm. The screen went black and the blue power light flickered a moment than went steady blue. There was a burning smell so I am assuming something was blown up!

While checking for blown capacitors I found a burn. Not sure exactly what it is. Hoping that you guys can help.

The degraded glue plague again. Those can cause anything from shorts to electronics behaving improperly/oddly. Your board has lots of them there in a few places. That blackish thingy coming off the transformer bottom could be the source of pungent burnt smell (again, with the degraded glue there)

@budm - I did as you suggested and removed as much of the glue as I could. That stuff is baked on there though

Scrape them off as much as possible, especially those that adhere to the exposed leads.

[McEugene]

Re: Samsung SyncMaster 2493HM black screen

solved case that worked for me after all procedures above failed in my case:
my psu is a BN44-00195A model 245B2 (slightly different part numberingfrom schematics above)
symptom was:
a black screen with blue power light steady on.
5,2V standby power was ok, primary PFC voltage was ok (380V for my european 220V input monitor). but the backlight 24V was not there ...(5.3V was not their either since it is a byproduct of the main 24V output...).

what I did:
A) replaced most polarized cap though all my caps looked ok (no bulging top)---> still black screen
B) checked for the yellow glue becoming conductive, clean up a couple of components ---> still black screen (no 24V out)
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)
pin 8 non inverting output of error was 5.1V =(ref voltage of the IC) --> force max oscillator frequency in principle...

pin 10 fault input was low when I mesured it...so in principle all was ok , no fault detected ...
By reading the datasheet of the IC , I noticed that if there was a pulse greater than 1v on the fault pin the IC would lock itself to prevent serious damage and remain in that state until power is removed...
It was a long shot but I decided to connect my DSO (! use double 12V-220V AC 3A transformers back to back on the 220V ac input to allow the whole supply to float and prevent to blast my scope inputs!!!! Ov of the scope is connected to earth in principle...)
So, i measured (captured) the Pin 10 level as I flipped on the power switch of the PSU and I noticed a tiny 10ms 1.1V pulse on the fault line after 200ms then the line was perfectly below the 1V threshold of the fault input pin (pin10)...I was nearing the solution.
There are two separate circuits tha can trigger a fault condition on pin 10:
1)- the overvoltage monitoring circuit via opto PC802S on the schematics(PC804S on my PSU model)
2) the "feedback/monitoring circuit" from the primary of the TM801S transformer (DM805-CM809-RM815 on the scematics)

on the overvoltage monitoring circuit, I disconnected the 0 ohm resistor (it not on the schematics, but on the PCB is is easy to find by following the tracks)
between the PC802S opto led cathode and the LMBT2222 transistor to desactivate that circuit and measured again the power up sequence on pin 10 ---> the 10ms pulse high was still there....
Then,
I checked carefully feedback components from the the primary of TM801S transformer and noticed nothing abnormal at first, then I notice some of that yellow hardened glue on the 47pF 1KV capacitor (CM809 on the schematics) in the feedback circuit. That glue was covering both legs of the capa!!! It was a long shot but I decided to desolder the capa and clean it up as nice as possible without breaking it...soldered it back...and it WORKED! The MC3306P was oscillating nicely and the 24V was back, I reconnected the 0 ohm resistor of the other monitoring circuit and all was OK.
My 2493HM monitor is back to life and so far it as been working perfectly again...

So my advice is CHECK the Yellow glue on all critical components and remove it if you can!!!

Now I know that PSU quite well since I have been working on it for a complete day or so....Since I have two of those monitors I am ready for the second one when it fails (hope not but...)
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