Samsung syncmaster 305t blank monitor, no light from the power LED

[JEBONE]

Hi,

I have a bought an out of order Samsung Syncmaster 305t cheap in the hope of being able to fix it. The problem is that when connected to the AC outlet it would not start, and the LED on the power button does not light up.

I have picked apart the screen and when checked the power supply I saw that the large capacitor (450v, 150uF) was bulged. I then replaced the capacitor with the same values, even the remaining capacitors are replaced with new ones. Then I put together the display and connected to the outlet, nothing happens, still black and the start button does not light up.

I have the six new capacitors to the inverter board but have not put them there yet. Is it possible that it may be faulty?

The power board: BN96-03938A if it helps.

I have include a picture of the power board.

Any idea about what I should look at next?

Tanks,

Jon Brodén

[selldoor]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Pictures need to be a little sharper for troubleshooting - we need to be able to read what it says on the board. Have you tested the 3 fuses? 2 white near the mains and a green torpedo one in the middle of the board.

[budm]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

I will first find out if you are getting the standby 5v (or 3.3v) voltage first, it is generated by the smallest yellow transformer close to the heatsink.
Are there any labels on the power supply connectors.
This power suply also has PFC Voltage booster circuits, the voltage on that large cap should be around 160vdc, then it should go up to around 390VDC when power switch is activated.
No blown fuse?

[selldoor]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Budm he is in sweden so voltage on cap will be around 325vdc? to start with

[JEBONE]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Tanks all for the quick replies!
added some new pictures that might be better.

Pictures need to be a little sharper for troubleshooting - we need to be able to read what it says on the board. Have you tested the 3 fuses? 2 white near the mains and a green torpedo one in the middle of the board.

The other two fuses are intact.

Is it the green thats looks like a resistor where the large capacitor is? measured it with ohmmeter over the fuse and the measured zero ohms, or do I need to solder away and measure to be correct?
I have a red ring around that I believe are the green torpedo fuse in the first picture.

I will first find out if you are getting the standby 5v (or 3.3v) voltage first, it is generated by the smallest yellow transformer close to the heatsink.
Are there any labels on the power supply connectors.
This power suply also has PFC Voltage booster circuits, the voltage on that large cap should be around 160vdc, then it should go up to around 390VDC when power switch is activated.
No blown fuse?

I measured the small yellow transformer on the secondary side, the measuring between 3.4-3.7V

Do I need to take some precautions when to measure the high voltage?
Should I measure in parallel over the the large capacitor?

In the fourth and fifth image is of power supply connectors.
from top to bottom on the picture it says GND, 5.4V, 1.8V, GND, N.C, GND, 24V. on the fourth and the fifth picture from top to bottom in the picture 6.0V, GND, Power on / off.

[budm]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

"top to bottom on the picture it says GND, 5.4V, 1.8V, GND, N.C, GND, 24V. on the fourth and the fifth picture from top to bottom in the picture 6.0V, GND, Power on / off."
So what voltages do you get at those pins, black probe on the chassis (cold side circuit's ground), red probe on those pins.

[JEBONE]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

"top to bottom on the picture it says GND, 5.4V, 1.8V, GND, N.C, GND, 24V. on the fourth and the fifth picture from top to bottom in the picture 6.0V, GND, Power on / off."
So what voltages do you get at those pins, black probe on the chassis (cold side circuit's ground), red probe on those pins.

GND, 5.4V, 1.8V, GND, N.C, GND, 24V: I get only a few mV on each output.
6.0V, GND, Power on / off: 6.0V output, I get 6V and Power on / off, I get a few mV and when I press the power button at the front, I get 3V

[selldoor]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Yes that is the green fuse if it measures 0.00 ohms it is good .

[selldoor]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

GND, 5.4V, 1.8V, GND, N.C, GND, 24V: I get only a few mV on each output.
6.0V, GND, Power on / off: 6.0V output, I get 6V and Power on / off, I get a few mV and when I press the power button at the front, I get 3V

Is that with all boards connected?

[JEBONE]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Strange now that connected everything together connected AC outlet, started the monitor, but it is flashing red, green, blue, gray and off, red, green ..... loops around so.
has now also 5.4V, 18V, 24V on outputs.
Is it possible that main processor chips that are faulty or?

[selldoor]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Have you got a source connected the rbgw may be a self test that displays instead of
"NO Signal"

[budm]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

OK, so this power supply board has 6v for standby power supply, the 5.4v, 12v, 24v are switched on when PS_ON (POWER ON/OFF) goes >3vdc.
But right now it powers up OK. You may want to check solder joints, etc, on the power board.

[JEBONE]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Thought Iwould notify the screen works fine now. maybe I'll check solder joints if it would die again.

Thanks a lot for your help everyone

//Jon Brodén

[Habtay]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

I have the same problem with exactly the same PSU, no power at all on the secondary side of the small yellow transformer. There is power on the primary side (80V relative to ground, 165V across) any help is highly appreciated. I can use a digital meter and soldering iron but not sure how the power supply circuit works.

[Habtay]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

I will first find out if you are getting the standby 5v (or 3.3v) voltage first, it is generated by the smallest yellow transformer close to the heatsink.
Are there any labels on the power supply connectors.
This power suply also has PFC Voltage booster circuits, the voltage on that large cap should be around 160vdc, then it should go up to around 390VDC when power switch is activated.
No blown fuse?

Hi there,
I am a new member and I have the same monitor with the same problem up to this message, on mine I'm not getting the 5v or 3.3v, no volt at all on the secondary side of this transformer. There is power on the primary side of this transformer. there is also power on the big capacitor (150uF, 450v) 165v.

Can some one please direct me on what to look next.

[MikeBeachBum]

Re: Samsung syncmaster 305t blank monitor, no light from the power LED

Hello all,
I get a lot of information from these forums so I would like to help anyone who had the same problem as I did.

Samsung 305T
Absolutely dead, no lights anywhere on the system.

My first thought was either fuse or cap. These monitors, while beautiful, have a poor reputation for heating up. Anyway, I opened it up (very easy to do btw) unscrewed the power supply, put it on a bench. The fuses checked fine. I plugged it in and looked at various voltages. All the voltages I checked (maybe 10 points) looked fine. Hmmm... So I plugged it back in, flipped on the toggle switch next to the power plug, and the blue light on the front power switch came on. I put the unit back together, put it back on my desk, plugged it in, no blue light. Repeated the whole process over again, and it appears to be one of the four ribbon cable connectors that go into the power supply. I don't know which one, but if I carefully made sure that they were are seated firmly, the unit would power on reliably. Anyway, no the most scientific debugging, but I'm hoping it helps someone somewhere.