Another SAMSUNG 2493HM !

[budm]

Re: Another SAMSUNG 2493HM !

RM801 is 0.22 Ohm (red/red/silver) 5% 1W Flame proof MOX (Metal Oxide). You MUST remove ALL the glues.

[smurtz]

Re: Another SAMSUNG 2493HM !

Thanks

[McEugene]

Re: Another SAMSUNG 2493HM !

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...)
McEugene is online now Report Post

[smurtz]

Re: Another SAMSUNG 2493HM !

wow , thanks for this very detailed post ! I thought the hard glue became conductive only when becoming brown, I'll try that

[budm]

Re: Another SAMSUNG 2493HM !

Bad glue.

[Behemot]

Re: Another SAMSUNG 2493HM !

I got this one which was recapped somewhen in the past (caps are already dusted so it is some time). This time the 0R22 resistor exploded and both switchers were blown as well (whoever knows in which order).

Haven't found anything else bad so I've swapped the switchers for FQPF13N50C (original were 9N50C so that should be OK). With lightbulb in series, it (the bulb) just blinks briefly when I start it up which does not suggest any serious problem on primary. However, I get only 324 V on main cap. This makes me wonder if the PFC is in low power state or what, but still, it should work even on this lower voltage, no? But I get nothing on secondary at all. Not the +5,4 V nor the +24 V.

I can't hear much because of air conditioner but I think there is no clicking or something so no short and stuff. What can I check now? Is it posible the PFC is not working right thus the controller does not get OK signal and main controller does not operate than? The PFC controller is Fairchild FAN7530 and it has 2,08 V on INV pin so it should be operational.

ADD// I think I am getting somewhere. There is only 10,62 V on the STR-A6159 primary driver which requires at least 16 V to start.
ADD2// I DO get the stand-by rail so it (the smaller voltage) seems to not be a problem

[budm]

Re: Another SAMSUNG 2493HM !

Since the 5VSTBY for the main board is not working, then the power supply will not get the PS_ON signal from the main board to turn on the PFC Voltage booster and the 24v power supply section. I would try to locate the problem in the 5VSTBY first, the AUX winding of the 5VSTBY is used to generated the B+ to run the PFC IC and the 24V SMPS IC.

[Behemot]

Re: Another SAMSUNG 2493HM !

I've corrected that statement, I do get 5,23 volts on the +5 V SB.

ADD// damn it, I wonder what's wrong and the bloody light bulb burned

Stupid question, but I am not really sure TBH. If I use 60W lightbulb, it should stay dark as well, right? I connected the rest to the power board, thought that maybe I just need to push the PWR ON button But when I turn the power on, bulb flashes, than goes off and than immediatelly on full brightness. Is it good or wrong? I think that the display draws some power when starting so it may need higher current which makes the bulb to go on? Should I keep it on for a few seconds or is it more like something getting shorted in the monitor so I should turn it off immediatelly (what I am doing)?

[budm]

Re: Another SAMSUNG 2493HM !

2493 Power consumption is 100W, you can disconnect the cable to the inverter board so it will not draw so much power, I use 100 watts lamp, it should come on full bright when you hit the power button, then should dim down.

[Behemot]

Re: Another SAMSUNG 2493HM !

I can get even 25W bulb so is it better to use smaller or bigger?

It flashes probably as input filtering charges, than dims and than goes full on. So can I keep it for a few seconds to see whether it dims (=everything OK) or continues to glow (=problem)?

[budm]

Re: Another SAMSUNG 2493HM !

25w is way too low. It goes bright when first charging up the cap, then dim down and when the power switch is activated, the PFC, the 24V, the inverter will then start drawing more current. It is tricky some time to determind if you truely have short circuit in the circuit that needs to be turn on. I use 100w on most of small monitor. So try it with inverter not connected.

[Behemot]

Re: Another SAMSUNG 2493HM !

I have 100W bulb too so I'll use that, thanks. As for the inverter, I haven't connected it yet…

[Behemot]

Re: Another SAMSUNG 2493HM !

I am more and more confused. With 60 W bulb, if I keep it go for a few seconds, it starts to blink and after another couple of seconds it goes fully on. If I use 100W bulb, it stays fully on and than dims completelly.

I have brief voltage spike on displays secondary (both 24 V and 5,3 V) than it goes off. The PFC seems to work just fine, voltage jumps to aprox. 350 V instantly and than rises all the way to 390 V on input cap.

The question is, is there some problem and is that 2 seconds to black/off, or is it just turning off because of, well, what. As for the inverter, to be more precise, I have connected it, but the backlight CCFLs are disconnected.

Anyway, since it seems that there is 390 V all right on the input cap, nothing is exploding and the 100W bulb goes off after a while (when the cap gets fully charged), I would say, primary is fine so I may go on and try unprotected mains?

[budm]

Re: Another SAMSUNG 2493HM !

You have to remove the power cable to the inverter, it draws lots of current. Removing the lamp connectors will not stop the inverter from trying to start up. So far it seems to be OK, but still should check the output voltages without the inverter connected.

[Behemot]

Re: Another SAMSUNG 2493HM !

Same behaviour, got spike on output than it goes off.

[Behemot]

Re: Another SAMSUNG 2493HM !

Hot test is OK so far that nothing exploded or so. But screen is still black so as before, I don't get main secondary output, only the SB rail (thus blue LED).

[budm]

Re: Another SAMSUNG 2493HM !

Is your board BN44-00195A or other model? So far it looks like you have the PFC and STBY working but not the 24v SMPS.

[Behemot]

Re: Another SAMSUNG 2493HM !

Yep, this board and this problem.

ADD// I think I am getting somewhere. The MCP33067P controller has 0 on Vcc.

ADD2// I went through some older topics and it occurs to me that in order to turn the main SMPS on, logic board sends continuous 3+ V signal on the PS ON pin. So if I want to test the SMPS without the logic board, I may just jumper that with +5 V SB, otherwise it won't turn on?

[budm]

Re: Another SAMSUNG 2493HM !

1K resisttor between PS_ON and 5VSTBY pin to fprce on the power supply PFC and the 24V SMPS without having the logic board connected, that is how I test the power supply.

[Behemot]

Re: Another SAMSUNG 2493HM !

OK when I do this I only get 12,48 V on the Vcc. The problem seems to be even before that linear regulator on this supply line, from what I read in older threads here it is supposed to have 27 V on input (from 27V zener) and than the output is lowered by the regulator, probably to them 20 V or so to feed the SMPS controller. There is just 13,5 V on the regulator.

So do you think the zener is bad or there is another problem?