Another SAMSUNG 2493HM !

[smurtz]

Hi all,

I've been trying unsuccessfully to resurrect my 2493hm reading throught
badcaps.net

It started like that: I tried to switch it on and heard "pschtt" and the screen went immediately black.
The symptoms are the following: No image, the blue led stays stable, the 2493hm can be switched on & off from the front panel.

When telling in several stores that the screen was only 4 years old when it went dead I was told: "Sir, nowadays, most of the screens & tv last an average of 2 to 3 years..."

THAT annoyed me a bit and I'd like to prove them wrong !

Attached are the photos of the logic board & power supply.

The following threads helped me for the following below:
https://www.badcaps.net/forum/showthread.php?t=15796
https://www.badcaps.net/forum/showthread.php?t=15843
https://www.badcaps.net/forum/showthread.php?t=13366


Power supply BN44-00195A.

-The fuses are good (tested continuity)

I've changed all the electrolytic capacitors except the 82uF/450V.


connector CN852(BL/SOS/A_DIM/ST D_DIM/DBT):

Pin    OFF ON
DBT    0,2 0,2
ST/P_DIM 0  0
A_DIM   0  0 
SOS    0  0
BL    0  0

Connector CN851(S_B/NC*3/GND*3/5.4V*3/NC*2):

Pin  OFF  ON
PS_? 0   3,147
S_B  5,24 5,24
GND  0   0
NC  0   0
GND  0   0
5.4V 0,45 0,45
NC  0   0

Connector CN85 (ST/P_DIM/ADIM/SOS/GND/+24V):

Pin    OFF ON
ST/P_DIM 0  0
ADIM   0  0
SOS    0  0
GND    0  0
+24V   0  0,5

MC33067P ICM801
Using pin 4 as ground:

Pin  OFF  ON
1   0,01 5,05
2   0   5,05
3   0   2,54
4   0   0
5   0   5,08
6   0   0,06
7   0   0,06
8   0   5,05
9   0,03 14,62
10  0   0
11  0   0,19
12  0   14,05
13  0   0
14  0,01 0,32
15  0,04 15
16  0   5,04

Using pin 13 as ground:

Pin OFF  ON
14 0,01 0,35
12 0   13,91

At the back of the PCB near that MC33067P, I checked a few resistors:


STRA6159 chip ICB801S

Pins OFF  ON
3-1  0   0,02
3-2  14,44 16,51
3-3  0   0
3-4  0,44 1,09
3-5  315  385 <-- seems strange ?

A few resistor a the back near the STRA6159 chip:
RB816 99,45K Ohms
RB815 2,19K Ohms
RB813 4,16K Ohms


Tested in-circuit (power off):
RB??? (next to the RB802) 98,94 KOhms (brown black yellow gold)
RB802 98,70 kOhms (brown black yellow gold)
RB803 46,23 Ohms (yellow purple black silver)
RB808 2,2 Ohms (red black gold gold)
RB801S 33,08 Ohms (yellow yellow black gold white)
RX801S 750 kOhms (purple green, yellow kaki black)
RW801 0,5 Ohms (red red silver gold)


Logic board BN41-00962A:

I checked the following:
IC113 LF25:

Pin ON  OFF
1  3,25 3,25
2  0   0
3  2,5  2,5

IC305 6P807

Pin ON  OFF
1  5,22 5,22 
2  0   0
3  5,21 5,21

Could the STRA6159 be bad ? Should I change it or check something else ?

Thanks in advance for your help !
Yves

[retiredcaps]

Re: Another SAMSUNG 2493HM !

It started like that: I tried to switch it on and heard "pschtt" and the screen went immediately black.
The symptoms are the following: No image, the blue led stays stable, the 2493hm can be switched on & off from the front panel.

1) Excellent clear focused photos. A picture of your inverter board is also required.

2) If you heard a "pschtt", it could be arcing from the ccfls to the metal frame.

3) If you have no backlights, it implies

i) blown fuse in the inverter section
ii) shorted mosfet or transistor in the inverter section

4) A blue power LED implies your power and main board are likely working okay.

5) If the backlights are on and you have no picture, then we need a picture of the t-con/panel board. This board is at the top of the lcd and runs the entire length of the lcd. It may be underneath a metal shield. There is usually a SMD fuse and it could be blown.

6) Clarify "no image" with respect to #3 amd #5 above.

[Toasty]

Re: Another SAMSUNG 2493HM !

Along with retiredcaps comments:

Need a sharp - clear photo of the back of PSU in the lower left quarter. Starting from just above the horizontal black dividing line, and to the left of the vertical black line. Appears an SMD resistor is blown there.

Unlikely the IC is bad.

The rectangular blue cap on top to the left of the transformer has been a problem.

Discolored adhesive/glue has been a problem. Becomes conductive if it gets heated and turns a darker brown.

I see Nichicon and Panasonic caps. What brand/series are the other 3 that you used with the elongated "X" ?

T

[budm]

Re: Another SAMSUNG 2493HM !

"connector CN852(BL/SOS/A_DIM/ST D_DIM/DBT):
Code:
Pin OFF ON
DBT 0,2 0,2
ST/P_DIM 0 0
A_DIM 0 0
SOS 0 0
BL 0 0"

Since BL for Backlight on signal is 0, the backlights will stay off, this BL on signal is from logic board.
Is this the condition you are getting with the monitor hooked up to running PC?

[smurtz]

Re: Another SAMSUNG 2493HM !

Checked on the t-con/panel board:

Fuse F1 ok

R3 10K
R5 3,95K
R4 3,60K
R7 13K
R21 29,91K
R22 53,44K
R23 298
R24 47K
R27 980
R28 1,8K
R29 42,9K
R30 Variable > 3,1
R32 230K
R33 56,18
R34 6,21K
R35 1,2K
R37 10K
R38 333K
R40 68K
R43 12,45K
R44 10,33K
R45 10,40K
R46 680
R47 5,09K
R55 0,22
R56 0,23
R60 0,22
R63 Variable >3,1
R66 1,75K

the 2200uF is a Panasonic FM serie
the 35v 1000uf is a NIC Components NRSZ serie
All the others are nichicon PW series

Toasty, it seems you have an "oeil de lynx"
The RT852 looks as if it's blown (psu_solder_detail05.jpg), however, my ohmmeter gives a reading of 224,25 Ohms (Is it the expected value ?)

@Budm: There is no backlight at all, even when connected to a pc

The requested pictures attached.

Yves

[retiredcaps]

Re: Another SAMSUNG 2493HM !

@Budm: There is no backlight at all, even when connected to a pc

As budm mentioned, the backlight on is generated by the main board. When you press the on/off button repeatedly, does this BL change voltage at all?

[Toasty]

Re: Another SAMSUNG 2493HM !

24v is dead.

Resistor is 100Ω. Transistor to the right is likely blown, and the 24v zener is probably bad too.

The buzzing could be a short/arc to frame, as RC mentioned. Or, just bad tubes.

Do you have 5.3v standby? Remember that ground on the LEFT of vertical stripe is different than that on the RIGHT (HOT side).

Check the 245BW threads. Same PSU is used and I did a bit of work on that with the last thread:
https://www.badcaps.net/forum/showthread.php?t=18966

T

[newbie1]

Re: Another SAMSUNG 2493HM !

Checked on the t-con/panel board:
Toasty, it seems you have an "oeil de lynx"
The RT852 looks as if it's blown (psu_solder_detail05.jpg), however, my ohmmeter gives a reading of 224,25 Ohms (Is it the expected value ?)

Yves

Hi,

Maybe I could help you later, when i reach home from work, to see what is the marking on the RT852.
I have 2 of this Power board but the monitor could not be revived yet, because i SUSPECT that both the Mainboard IC connected to them are having main IC shorted.link
It may not be applicable to your case but i recalled having done once with similar symptom of yours, Steady Power LED but no backlight. I did a resoldering on the power board (could not remember which component though) and it came back to life..

Off track, OP , if you have the time, can you help to measure the points of the VDDC of the Main IC300 (on the Mainboard). Mine is reading, resistance measured from VDDC (+1.8V_live) to Gnd (screw ring of the mainboard) is 30ohms one way & 100ohms when reversed. You can do the measurement across either of the tiny capacitors of the VDDC rails (C332, C334, C335, C336, C337, and C338).

I am now trying to Mod the monitor by purchasing a 245bw main board as replacement because it is difficult & costly to find the Mainboard for 2493hm.

Edit : well Toasty have beaten me for the RT852 info..

[smurtz]

Re: Another SAMSUNG 2493HM !

The buzzing could be a short/arc to frame, as RC mentioned. Or, just bad tubes.

I think I didn't express myself clearly from the start (pardon my english):
What I meant by "I tried to switch it on and heard "pschtt" and the screen went immediately black." is that the noise was really short and lasted the time for the screen to go black (that is, almost instantly). Now the monitor is perfectly quiet.


I indeed have the 5.24v standby.

Following the thread you mentioned, I check the 82uF cap , it reads 385V power on.
For the 2 components (DZT851 and QT851) next to the RT852, I get readings that seem ok (I'll post them tonight). But since I need to order a 100Ohm resistor, I'll order the two others as well & change them.

@newbie1: I'm not at home right now, I did the measurements yesterday night but do not remember the readings,I'll post them tonight.

Yves

[smurtz]

Re: Another SAMSUNG 2493HM !

Here are my results :


QT851:

B E 9,9K /9,9K Ohms
C E 0 / 3,4M Ohms
B C 3,30M / 0 Ohms

DZT851

0,591 / 0 in diode test mode
1,29M Ohms / 9,6M Ohms using the resistance mode

@newbie1: from C337 to gnd : 1,20V (monitor on or Off), 81 Ohms (gnd to c337) and 125 Ohms reversed

Yves

[dylanneke]

Re: Another SAMSUNG 2493HM !

does anyone have a schematic on this board?

[Toasty]

Re: Another SAMSUNG 2493HM !

QT851 looks to be shorted B to E. It's a 1P transistor. Common as they come.

The emitter sits on ground and explains why the resistor burned.

DZT851 & DZT852 are zeners. They sit on the 24v and 5.3v and output to DT851 a dual diode. It's a protection circuit that watches if the 2 voltages get out of line (either zener conducts) and through RT852, trigger QT851 to conduct. That in turn, enables the optoisolator PC804 (top one of the 3 to the right), which sends a signal (via a transistor and resistor) to ICM801, pin 10 (fault input), causing the PWM to shut down.

The 24v "makes" the 5.3v when running. Removing QT851 may allow the unit to come on and you can verify operation and voltages.

Whew!

Time for a nap....

[smurtz]

Re: Another SAMSUNG 2493HM !

Wow!

Before removing the QT851, 2 questions:

- Since it's in a protection circuit, could removing it damage the logic board connected to the psu board ?
- What is the reference of the DT851 & DZT852 (If I order parts I'll order one of these as well to save on shipping...) ?

Thanks for your help !

Yves

[budm]

Re: Another SAMSUNG 2493HM !

So anyone has the SCH for this BN44-00195A?

[Jasgriff]

Re: Another SAMSUNG 2493HM !

Looks like that powerboard is the same one that was used in this previous thread. Might be wrong though?

https://www.badcaps.net/forum/showthread.php?t=18760

[Toasty]

Re: Another SAMSUNG 2493HM !

There is no schematic for the PSU. We've been looking for a long time...

@smurtz - no, removing it will not harm it provided you watch the 24v and 5.3v lines to make sure they don't go out of spec. A short run time of a minute or so to prove operation is all that is necessary.

Search for 1P transistor on the forums. Should see plenty of numbers, especially in the Apple PSU threads. The zeners are another matter... Got the last batch through Avnet.

[smurtz]

Re: Another SAMSUNG 2493HM !

Excellent ! I have the 5,4 & 24V !

After removing the QT851:

CN85:

Pin    OFF ON
ST/P_DIM 0 2,41
ADIM   0  4,56
BL    0  4,56
SOS    0  0,55
GND    0  0
+24V   24,3 24,3

On the CN851

Pin  OFF  ON
PS_? 0   3,147
S_B  5,24 5,24
GND  0   0
NC  0   0
GND  0   0
5.4V 5,42 5,42
NC  0   0

However, on the psu in the area where I removed the QT851, a slight continuous & stable buzz appears 1 or 2 seconds after having the monitor swhitched on. could it be normal ?

Yves

[smurtz]

Re: Another SAMSUNG 2493HM !

Hi,

I changed QT851, DZT851 & RT852...


Voltages are:

CN851

Pin  OFF  ON
PS_? 0   3,147
S_B  5,24 5,24
GND  0   0
NC  0   0
GND  0   0
5.4V 5,42 5,42
NC  0   0

Here is a change:

CN852

Pin OFF ON
DBT   0,2 5,34
ST/P_DIM 0 2,2
A_DIM  0 5,34
SOS    0 0,45
BL    0 4,49

There is a slight continuous buzz when the psu is on, but you can't hear it when everything is put back in place.

and..... the monitor works again ! I hope it will last

Toasty,newbie1,budm & retiredcaps a big big BIG thank to you all !
For less than 40Euros I avoided throwing the thing to the bin, that's cool !

Yves

[mengfei]

Re: Another SAMSUNG 2493HM !

I have exactly the same problem as this!
I turned ON the main switch & the monitor showed the blue light then I powered On the PC & heard "pschtt" sound also. PC is fine with other mon.

So Far I have checked all the fuse including the SMD & they seem to be fine.
2493HM Blue Power Led On but totally black screen, will check voltage next time.
thanks to this thread.

[smurtz]

Re: Another SAMSUNG 2493HM !

ok, back one year later on the same monitor !

I suddendly heard a big >clac< a flash at the bottom of the back side of the monitor and a little smoke : black screen....

I opened it again and found a resistor on the power board that is all back and when tested reads 6,5 MOhms (RM801).

Tested QM803 and QM801 they are shorted.

unlike here, TM801 seems ok:

https://www.badcaps.net/forum/showth...ghlight=2493hm

Going to order 2 FQPF9N50C and a resistor to replace the RM801
but I need 2 infos:

- What is the value of RM801 ?
- and do I need to replace or check something else
preventively ? (caps have already been replaced)


https://www.badcaps.net/forum/showth...t=22008&page=2

Thanks