Samsung syncmaster t220 Powers on no screen.

[ratboy99]

Re: Samsung syncmaster t220 Powers on no screen.

any other advice on what my problem might be?

[newbie1]

Re: Samsung syncmaster t220 Powers on no screen.

I am not sure how Q601 looks like or what is the top marking, but how about checking whether it is shorted out?. with power unplugged, i usually measure the resistance between the 3 legs.

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

Service manual:


If you look at page 4-3, Q601 is bias on (transistor is turn on by the processor, there will be about 0.6V between Base and Emitter) when the monitor is off or in standby mode, this will cause the CN600 PIN8 (BL_EN, there is pull-up resistor R600) to be LOW, when the drive signal from the processor that drives the Base of Q601 goes LOW, Q601 will turn off which will cause the Collector to go HIGH (BL_EN CN600 PIN 8) which will turn on the backlights. So check and see if Q601 has shorted Emitter to Collector or not, or if the Base drive signal stuck HIGH all the time which will make the BL_EN line at pin 8 to stuck LOW.
If you short the Base and the Emitter together (but you have to find out if the transistor is OK or not first), that will turn off the transistor, then the backlights should turn on, or you can remove the Q601.

[ratboy99]

Re: Samsung syncmaster t220 Powers on no screen.

that wiring diagram helps a lot. I have to make another move from oregon to LA one last time so i've packed the monitor up rather then fix it now and chance that it has another problem in the truck again. i'll be back on here in a week or so after my move to start poking around the monitor some more.

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

Hello!

I have the same problem: Power on (red LED is on), but no screen (no backlight and no image!)

- I've checked the voltages at the connector:

1 -> 3.9V (BL_ADJ_PWM)
2 -> 14V (+14V)
3 -> 0V (GND)
4 -> 0V (GND)
5 -> 5.24V (5V_IP_1)
6 -> 5.24V (5V_IP_2)
7 -> 3.5V (BL_ADJ_ANALOG)
8 -> 0V (BL_EN)
9 -> 3.29V (+3.3V)
10 -> 2.95V (LED)
11 -> 3.04V (KEY1_OUT)
12 -> 1.77V (KEY2_OUT)

- Based on the voltages that I'm getting, the capacitors seems to be OK. No leaking or bulging.

- Connecting the Q601 transistor's base to GND starts the backlight.

- Voltages at main board test points:
+4.24V (+5V_MAIN) (15% OFF)
+3.16V (TP1) (Should be 3.3V. 4% OFF)
+1.77V (+1.8V) (5% OFF)

(NOTE: If I connect the LVDS ribbon, voltages rise to their correct values!)

Any suggestion?

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

The main board is not sending the BL_EN (BL_ON) to turn on the backlights.
Pictures of the boards?
Correct Voltage (5 or 12V) at the T-CON board SMD fuse?
3.16 FROM 3.3V REG is too low. may be bad IC or bad caps, or too much load.
5V is also too low.

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

I can turn on the backlights by manually triggering the BL_ENABLE signal.

Measurements are made with the LVDS ribbon cable attached at the logic board and the CCFL lamps detached from the power lamp, as it's physically difficult to hold all the circuits together.

I don't know how to locate the T-CON board SMD fuse....

Yeah, 4.38V for 5V_MAIN seems to low to me.
3.16V is actually 3.28V (my fault... I measured it with the LVDS cable detached).

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

Pictures of the T-CON board? It is a long board attached to the LCD panel.

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

There's yet a hidden board!

Ok, I took a picture and I tested the F1 SMD device with a multimeter. I guess it's a fuse and it reads 0.1 ohm, so I think it's not blown.

Should I take new measurements with the power on? Do you need any other picture?

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

So what DC Voltage do you have at both ends of the fuse when monitor is on and connected to running PC?

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

When power on, voltage at:

- Both ends of the fuse
- 5V testpoint
- 5V_PANEL testpoint at the logic board

are all 0V

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

When power on, voltage at:

- Both ends of the fuse
- 5V testpoint
- 5V_PANEL testpoint at the logic board

are all 0V

You did the test with the unit's on and connected to running PC? If that is the case, then the logic board is not sending the Voltage to run the T-CON board.
Right now it seems to be logic board problem, it is not sending the BL_ON either.

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

Service manuals:
I'm not sure the exact model you have.
http://elektrotanya.com/?q=showresul...nitor&kat2=all

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

Ok. I have taken a look at the service manual and I identified the part that converts 5V_MAIN into 5V_PANEL

0.69V at PANEL_EN.

At the MOSFET I have 4.06V at GATE, 4.47V at SOURCE and 0V at DRAIN. Regardless if LVDS ribbon is connected or not.

So, MOSFET is blown? Here I attach a diagram. Could you confirm my guess, please?

(MOSFET's datahseet: https://cdn.badcaps-static.com/pdfs/...ea60120791.pdf)

(Thank you for the service manual :P)

EDIT: The part that converts 5V_IP to 5V_MAIN is also a mosfet (same datasheet). I have not taken measurements yet, but it could be also damaged (and therefore, the low 5V_MAIN [4.3-4.5V] value). I'll do it tomorrow (1:52 AM right now in Spain. Good night!)

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

So which one is the correct service manual for your monitor?
Per SCH:
The switched MOSFET Q206 is the P-CH, so the Gate voltage has to be 4V less than the SOURCE pin Voltage for it to be fully ON, right now the MOSFET is not turned on.
The MOSFET will be turned on when Q202 is turned off (no E-B Voltage of 0.6V, Q202 is on right now) which will make its Collector Voltage of Q202 to rise which will then turn on Q205 which in turn take the GATE Voltage of MOSFET to be below 1V.
You can force on by shorting the E-B of Q202, then you will have Voltage present at the Drain pin (+5V panel) of Q206.
You should see the E-B Voltage of Q202 toggle on and off if the processor is sending the signal for turning the panel on and off.

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

The service manual is "SAMSUNG LTW22HS LTW22GS LTW20HS CH LTW20GS T220 T220G T220N T220GN T200 T200G T200N T200GN"

So, from the test that I performed:

- Power board is working OK.
- No visible signs of damage.
- The problem is on Logic board, since it's not sending the correct signals.
- 3.3V and 1.8V are present and powering the scale chip.

Maybe a "software" problem? corrupt EEPROM or something like that?

I say that because the scaling chip is somehow working: The power button reacts an change when I touch it. In addition, if I freshly connect the power cord, it starts blinking with short bursts. That beaviour suggest me that the scaling chip is working (more or less), since the LED is controlled directly from the GPIO ports.

Thank you for the explanation on how the MOSFET switch works

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

Ok.... I decided to discard the screen.

But before I wanted to try a last and fun bullet: The homemade poorman's reflow technique.

I put the logic board in an oven, and I left it there several minutes. I roasted it a bit. I know The connectors almost melted and now is brownish.

But... Now I'm getting 5.15V at 5V_MAIN, the BL_EN (2.5V) and 5V_PANEL signals appeared and they are consistent with the ON/OFF keypress.

Tomorrow I'll assembly the whole screen and see what happens. I must admit it: I'm excited with that xD

[budm]

Re: Samsung syncmaster t220 Powers on no screen.

How hot did you set the oven to?

[Moki_X]

Re: Samsung syncmaster t220 Powers on no screen.

Well.... I tried to mimic the reflow curve, with the help of an infrared thermometer. The connectors were somewhat protected with tin foil.

- At first I let the oven preheat to ~150ºC
- Then I placed the board and let it there a couple of minutes
- After that, I turned on the second heating element.

I would say the temperature was ~200-230ºC. But, anyway, it's hard to say.

The big capacitors were probably damaged due to high temperature

In any case... that was a success for me. The screen is working again :P

Here's my report. It may be useful to someone in a future:

Symptoms: Whe the screen is turned on, the LED turns on an react to kepress on the ON/OFF touch button. But NO IMAGE at all. Not even the pale image tipically associated with backlight failure. No image when inspected with flashlight.

When unplugged and then plugged again, the ON led start to flash with shorts bursts.

List of steps that I followed:

1. General disasembly and visual inspection: capacitors at power board were visually OK and no visible damage anywhere.
2. Fuse testing -> They were OK.
3. Checking voltages at the power board -> Voltages OK. BL_EN signal was missing. I'm start to suspect a failure of the logic board.
4. Manual triggering of BL_EN made the backlight lit. Power board discarded!
5. Checking T-CON board fuse. It was OK, but there was no voltage. That's suspicious...
6. Checking voltages at the logic board: 5V_MAIN was a bit low. 3.3V was OK, 1.8V was OK.
7. Checking signals: 5V_PANEL was 0V. Signal PANEL_EN was HIGH -> Scaling chip was telling the board to keep the panel shut off.
8. Performed reflow of the logic board. Mounting and testing showed the BL_EN signal and the 5V_PANEL were finally there!
9. Final assembly

Thank you budm for your help!

[eniac22]

Re: Samsung syncmaster t220 Powers on no screen.

I have also problem with this monitor, backlight is working for 1 sec and then black screen, i check the capacitors with a esr meter and seams to be good.

- I've checked the voltages at the connector:

1 -> 0.11V (BL_ADJ_PWM)
2 -> 15.38V
3 -> 0V (GND)
4 -> 0V (GND)
5 -> 5.20V (5V_IP_1)
6 -> 5.20V (5V_IP_2)
7 -> 0.54V (BL_ADJ_ANALOG)
8 -> 2.56V (BL_EN)
9 -> 3.25V
10 -> 2.97V (LED)
11 -> 3V (KEY1_OUT)
12 -> 1.78V (KEY2_OUT)

any help?