Samsung 920NW 2 Seconds to Black

[Jasgriff]

Picked up a few monitors from an office clear out all with different faults so I have decided to play with this one first.

It seems to suffer from the same symptoms as the majority of similar Samsung models.

When starting it you can see the bios check screen the as windows would normally start to load the monitor auto adjust screen comes on a couple of times but windows does not appear. I also tried to F8 into safe mode which did show me the black and white option screen then it went off. when the screen goes off the options button do not display anything but the power light remains blue.

Here are the pictures for people to see what I am talking about. I am going go through retiredcaps step by step guide and post the results as I go.

I have managed to get my proper camera back so hopefully these pics will be butter than my last poor effort.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Checked the fuses they are fine :

F801 - 0.4 Ohms
F802 - 0.4 Ohms

Also found the service manual :

http://monitor.espec.ws//files/samsung___920nw_136.pdf

I tested the voltages on Pin 1 and Pin 2 which should both be 5V they are both reading 5.2v steady which is fine.

I placed a resistor between Pin 1 (5v) and Pin 4 (On) the backlight came on for 2 seconds that went off again. I unplugged the power and plugged it back in leaving the resistor in place and it still didn't come back on. When I unplugged the power and the removed one leg of the resistor then replaced it there was a very short flash of the backlight as if it was just using the stored power from the power supply. When I plugged the monitor back in again with the resistor in place it again came on for 2 seconds and then went off.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

CCFL's have been tested.

I connected each of the CCFL's into another Power supply and tested them one by one and they all light up and stay on for more than the 2 seconds.

I also tried all 4 CCFL's from another monitor on the Samsung Power supply and they light up only for a split second each time after being turned on.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Tried swapping out 2 of the capacitors on the off chance that it might have been those.

Samxon 1000uf 10v GK(M) Z1A Replaced with 1000uf FR 13VCS
Su'scon 1000uf 25v SG 0807(M) Replaced with 1000uf FR 144TG

These replacements are a lot smaller I hope that these are ok. These new capacitors didn't have any effect.

[retiredcaps]

Re: Samsung 920NW 2 Seconds to Black

I circled what I think are the secondary inverter transformer pins. Measure the resistance between the 2 red pins. Do the same for yellow. Report both readings. They should be within 3% of each other.

PS. The pictures are very good. It helps us help you.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Both readings were taken with my meter set to 2000 OHM's.

Red was 592
Yellow was 595

Just tested the diodes as follows. (These readings are with my DMM set to Diode)

Top Side
D804 = 561
D802 = 549
D806 = 618

Bottom Side
D501 = 611
D505 = 611
D513 = 604
D503 = 602
D504 = 606

ZD803 = 729

There is a bit of a burn mark around R804 could this have failed?

[budm]

Re: Samsung 920NW 2 Seconds to Black

How are the 4 very small blue ballast caps for the lamps, should Ohm them out also.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Will do...

DMM set to 2000 Ohm Scale
C523 = 608
C506 = 613

DMM set to 20m Ohms scale
C509 = 6.21
C528 = 6.94

Does that sound right?

[retiredcaps]

Re: Samsung 920NW 2 Seconds to Black

Both readings were taken with my meter set to 2000 OHM's.

Red was 592
Yellow was 595

Your inverter transformers are likely good.

There is a bit of a burn mark around R804 could this have failed?

If you have multiple 920NW's crack another open and check R804 for the color band and compare with this one.

[retiredcaps]

Re: Samsung 920NW 2 Seconds to Black

List the legend for CN801 and measure the DC voltage on each pin.

2 seconds to black can also be bad caps. If the caps are bad, one result may be unstable or low DC voltages going to the inverter section.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

CN801 is as follows

These reading were taken with a resistor from pin 1 to pin 4. with no logic board connected.

1 VCC5v = 5.2V
2 VCC5v = 5.2V
3 GND = GND
4 ON/OFF = 5.2V
5 Brightness = 0v
6 GND
7 Volume = Not Used
8 Audio Mute = Not Used

[alexanna]

Re: Samsung 920NW 2 Seconds to Black

CN801 is as follows

These reading were taken with a resistor from pin 1 to pin 4. with no logic board connected.

1 VCC5v = 5.2V
2 VCC5v = 5.2V
3 GND = GND
4 ON/OFF = 5.2V
5 Brightness = 0v
6 GND
7 Volume = Not Used
8 Audio Mute = Not Used

It would be a good idea to verify voltages on the 16 pin inverter controller IC501?
You will need to see if you can find a data sheet.
Verify power and grounds and that back light on signal is OK.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

These tests were done with a resistor across 5v and On/Off.

I can see from the service manual that Pin 10 of IC501 is the ON/OFF pin.

I used the negative pin of my DMM on Pin 14 which it says is ground (is that the correct pin?). With my positive probe on Pin 10 and I get 4.2v. Should that be enough to turn on the inverters?

I also tested the following....

Pin 14 - Pin 2 = 5.2v
Pin 14 - Pin 1 = 0v
Pin 14 - Pin 15 = 0v

U501

Pin 1 - Pin 2 = 0v
Pin 1 - Pin 4 = 0v

Pin 4 - Pin 5,6,7,8 all read 14.2v on U501 and U502

Should U501 and U502 have an on signal going to Pin 4 and Pin 4?

If there is nothing on the Dim Pin would this cause the screen to remain off?

[budm]

Re: Samsung 920NW 2 Seconds to Black

Are you getting steady 14vdc for feeding the Inverter circuits? Attach a 12v lamp (car lamp #1157) to it and see if it can handle the lamp. Do not hit the power switch when testing with the lamp since the power supply will be running when the monitor is plugged in, it runs 24/7 even when the monitor is off, unless the monitor has the real toggle/Rocker power switch that actually cuts off the power to the board

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Are you getting steady 14vdc for feeding the Inverter circuits? Attach a 12v lamp (car lamp #1157) to it and see if it can handle the lamp. Do not hit the power switch when testing with the lamp since the power supply will be running when the monitor is plugged in, it runs 24/7 even when the monitor is off, unless the monitor has the real toggle/Rocker power switch that actually cuts off the power to the board

I will have to pop out and buy a bulb tomorrow I will make sure that I get the 6v one at the same time.

IC501 is a OZ9938GN Pin 10 (ENA) is 4.2v that should be enough to turn on Pin 1 and Pin 5?

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Found the Inverter controller diagram.

I will work through the pins and feedback what im getting on each pin.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Are you getting steady 14vdc for feeding the Inverter circuits? Attach a 12v lamp (car lamp #1157) to it and see if it can handle the lamp. Do not hit the power switch when testing with the lamp since the power supply will be running when the monitor is plugged in, it runs 24/7 even when the monitor is off, unless the monitor has the real toggle/Rocker power switch that actually cuts off the power to the board

Got the bulb today and solder a couple of wires on. Could you please show me a couple of points on the board to solder this bulb to so that I can give it a try?

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Ordered the remaining capacitors. Hope they will arrive tomorrow so that I can eliminate them.

[Jasgriff]

Re: Samsung 920NW 2 Seconds to Black

Connected the bulb up and switched on the power. The bulb lights up then gets brighter as the inverter kicks in and powers up the back lights.

Whats very strange is that with the buld connected the backlight stays on for longer than 2 seconds?

I am guessing that I wired the bulb up wrong for this to happen?

Does this mean that the 14v line is definitely good if it can power the inverter and the bulb?

[budm]

Re: Samsung 920NW 2 Seconds to Black

But the backligts did go off later, right? You are doing this with the active PC connected to the monitor?
The bulb also lights up with steady brightness without a lot fluctuation and the voltage is steady at 14v or so?