GNR TS902W no power , help please

[lcdcaps1]

Re: GNR TS902W no power , help please

I get a reading of about 500 mV
what shall i test next, please

thanks so much for all your help in advance

Did you test the Drain-Source diode junction?

With positive (red) multimeter probe on Source and negative (black) probe on Drain, you should get a diode reading in diodes test mode - anywhere from about 400 to 800 mV, depending on other parts in the circuit. Reversing the probes should show nothing, both in and out of circuit - at least not when you keep the probes connected for more than 2-3 seconds (in order for your multimeter to bias any large caps in the circuit, so that they don't give false readings).

And when measuring the MOSFET out of the board from Gate to Source or Drain, regardless of the orientation of your multimeter probes, you should get open-circuit reading.

Additionally, you may be able to do a "basic" check of the MOSFET function when out of circuit with your multimeter by connecting the negative probe to Source and the positive probe to Gate. Then, if you remove the positive probe from Gate and touch the Drain lead with it, you should get a very low resistance/diode reading - ideally short-circuit. And if you touch the Gate lead with your finger, the MOSFET should turn off and the short-circuit between Drain and Source disappear.

[momaka]

Re: GNR TS902W no power , help please

i tested the transistor but get no readings

Did you test the Drain-Source diode junction?

With positive (red) multimeter probe on Source and negative (black) probe on Drain, you should get a diode reading in diodes test mode - anywhere from about 400 to 800 mV, depending on other parts in the circuit. Reversing the probes should show nothing, both in and out of circuit - at least not when you keep the probes connected for more than 2-3 seconds (in order for your multimeter to bias any large caps in the circuit, so that they don't give false readings).

And when measuring the MOSFET out of the board from Gate to Source or Drain, regardless of the orientation of your multimeter probes, you should get open-circuit reading.

Additionally, you may be able to do a "basic" check of the MOSFET function when out of circuit with your multimeter by connecting the negative probe to Source and the positive probe to Gate. Then, if you remove the positive probe from Gate and touch the Drain lead with it, you should get a very low resistance/diode reading - ideally short-circuit. And if you touch the Gate lead with your finger, the MOSFET should turn off and the short-circuit between Drain and Source disappear.

[lcdcaps1]

Re: GNR TS902W no power , help please

the markings on the mosfet are
k3562

what is the markings on the mosfet?

[rddube]

Re: GNR TS902W no power , help please

what is the markings on the mosfet?

[rddube]

Re: GNR TS902W no power , help please

No resistance readings at all?

[lcdcaps1]

Re: GNR TS902W no power , help please

i tested the transistor but get no readings

[rddube]

Re: GNR TS902W no power , help please

I think you might want to take a look at the components on the other side of where I marked it in the picture. It's hard to tell from the photos, but it looks as if something heated up here on the other side, probably the mosfet bolted to the heatsink.

Please let us know what resistance readings you get on that mosfet. Also, I am attaching a manual for a power board that is similar to yours, not exactly the same model but very similar...it might help.

[momaka]

Re: GNR TS902W no power , help please

Well, it's a process of elimination. Next up, replace the start up cap. If that doesn't help, replace the output caps. There's just no telling with those CapXon and Taicon caps in there which (if any) is bad. If that doesn't work, then we go further troubleshooting from there.

[lcdcaps1]

Re: GNR TS902W no power , help please

ok tested diodes all ok
have not replaced the start up cap yet

what elese can cause this please
thanks

That's be the start-up cap.

2.8 Ohms ESR is a bit high, but not too terrible for a small cap. I suggest replacing it first, to see if that brings the monitor back up.

But since you say you read no voltage on it at all, then check resistors R128, R129, and R130 (they are small SMD resistors on the solder side of the board, in the area of the start-up capacitor... and to the right of that SMD PWM controller chip). Looks like they are all 560 KOhm resistors (they have "564" written on them). See if any of them is open-circuit.


Yes.
You should get a diode reading in one way (positive multimeter probe on anode and negative probe on cathode), and nothing or very very high reading when you reverse the multimeter probes. If not, take diodes out of power supply and test them again. Out of circuit, they should definitely show no reading in the reverse direction.

[lcdcaps1]

Re: GNR TS902W no power , help please

I tested the resistors and all are ok within range
I have not replaced the start up cap yet but wanted to know
when i read the diode using diode mode what would be the approx values for both ways please

thanks

That's be the start-up cap.

2.8 Ohms ESR is a bit high, but not too terrible for a small cap. I suggest replacing it first, to see if that brings the monitor back up.

But since you say you read no voltage on it at all, then check resistors R128, R129, and R130 (they are small SMD resistors on the solder side of the board, in the area of the start-up capacitor... and to the right of that SMD PWM controller chip). Looks like they are all 560 KOhm resistors (they have "564" written on them). See if any of them is open-circuit.


Yes.
You should get a diode reading in one way (positive multimeter probe on anode and negative probe on cathode), and nothing or very very high reading when you reverse the multimeter probes. If not, take diodes out of power supply and test them again. Out of circuit, they should definitely show no reading in the reverse direction.

[momaka]

Re: GNR TS902W no power , help please

ok found the startup capacitor
, 10uf, 50v and there is no voltage on it

The esr is 2.8

That's be the start-up cap.

2.8 Ohms ESR is a bit high, but not too terrible for a small cap. I suggest replacing it first, to see if that brings the monitor back up.

But since you say you read no voltage on it at all, then check resistors R128, R129, and R130 (they are small SMD resistors on the solder side of the board, in the area of the start-up capacitor... and to the right of that SMD PWM controller chip). Looks like they are all 560 KOhm resistors (they have "564" written on them). See if any of them is open-circuit.

How do i test the diodes, continuity mode and same with transistors

Yes.
You should get a diode reading in one way (positive multimeter probe on anode and negative probe on cathode), and nothing or very very high reading when you reverse the multimeter probes. If not, take diodes out of power supply and test them again. Out of circuit, they should definitely show no reading in the reverse direction.

[lcdcaps1]

Re: GNR TS902W no power , help please

ok found the startup capacitor
, 10uf, 50v and there is no voltage on it

The esr is 2.8

That's not the start-up cap, that's your main input cap (CE106).
The start-up cap is that small one between the main transformer and primary heatsink. I can't read its board designator from the pictures, but it's usually something in the range of 4.7 to 47 uF typically and 25-50V. You will probably need to replace that cap. But before doing so, remove it from the monitor and check it on your ESR meter (and post the results here).

I see your power supply also has the original CapXon and Taicon caps, which could be another source of the problems. Might want to remove and check those on the ESR meter as well, if that small cap turns out not have failed (yet).

If those caps are not the problem, you might have a shorted output rectifier - that would be diodes D101 and D102 near the output caps. Also the TO-220 device bolted on a heatsink, again near the output caps.

And last but not least, there is a small white fuse on the bottom of the board labeled "P 260". That looks like a resettable poly-fuse, but check it with your meter anyways. Should give very low resistance (less than an Ohm or two, depending on how low your meter can measure).

Also, when you were checking the output voltages, was that with the power supply connected to the rest of the monitor boards or by itself?
I usually suggest checking LCD monitor power supplies by themselves, as many are of the "always on" -type (i.e. should be outputting at least one or more standby + main voltages).

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi

Please could you highlight the startup capacitor as i am not sure

I test all voltages on the power board on its own
The fuse is ok, i tested with continuity and it beeped

How do i test the diodes, continuity mode and same with transistors
please, sorry newbie qs

thanks

That's not the start-up cap, that's your main input cap (CE106).
The start-up cap is that small one between the main transformer and primary heatsink. I can't read its board designator from the pictures, but it's usually something in the range of 4.7 to 47 uF typically and 25-50V. You will probably need to replace that cap. But before doing so, remove it from the monitor and check it on your ESR meter (and post the results here).

I see your power supply also has the original CapXon and Taicon caps, which could be another source of the problems. Might want to remove and check those on the ESR meter as well, if that small cap turns out not have failed (yet).

If those caps are not the problem, you might have a shorted output rectifier - that would be diodes D101 and D102 near the output caps. Also the TO-220 device bolted on a heatsink, again near the output caps.

And last but not least, there is a small white fuse on the bottom of the board labeled "P 260". That looks like a resettable poly-fuse, but check it with your meter anyways. Should give very low resistance (less than an Ohm or two, depending on how low your meter can measure).

Also, when you were checking the output voltages, was that with the power supply connected to the rest of the monitor boards or by itself?
I usually suggest checking LCD monitor power supplies by themselves, as many are of the "always on" -type (i.e. should be outputting at least one or more standby + main voltages).

[momaka]

Re: GNR TS902W no power , help please

I checked the startup cap and got 324V

That's not the start-up cap, that's your main input cap (CE106).
The start-up cap is that small one between the main transformer and primary heatsink. I can't read its board designator from the pictures, but it's usually something in the range of 4.7 to 47 uF typically and 25-50V. You will probably need to replace that cap. But before doing so, remove it from the monitor and check it on your ESR meter (and post the results here).

I see your power supply also has the original CapXon and Taicon caps, which could be another source of the problems. Might want to remove and check those on the ESR meter as well, if that small cap turns out not have failed (yet).

If those caps are not the problem, you might have a shorted output rectifier - that would be diodes D101 and D102 near the output caps. Also the TO-220 device bolted on a heatsink, again near the output caps.

And last but not least, there is a small white fuse on the bottom of the board labeled "P 260". That looks like a resettable poly-fuse, but check it with your meter anyways. Should give very low resistance (less than an Ohm or two, depending on how low your meter can measure).

Also, when you were checking the output voltages, was that with the power supply connected to the rest of the monitor boards or by itself?
I usually suggest checking LCD monitor power supplies by themselves, as many are of the "always on" -type (i.e. should be outputting at least one or more standby + main voltages).

[lcdcaps1]

Re: GNR TS902W no power , help please

I tested the esr of the big startup cap and got a reading of
0.19 to 0.20

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi
Thanks for the reply
I checked the startup cap and got 324V
I did not change
It looks flat, i just checked

I checked all the voltages on the connector using the ground pin but nothing
i checked again using a screw hole, also nothing

[rddube]

Re: GNR TS902W no power , help please

As Momaka suggested, have you changed or checked the startup cap? Can't really tell from the photos but it looks a bit bulged?

Also, when you say there are no output voltages voltages, what are you using for ground for checking? You can't use the same ground as on the hot side of the power supply (do you see the line separating both sides of the PSU) ? Use a ground on the cold side of the PSU and measure the voltages that are on the connector (they are printed on the circuit board)....do you get anything?

[lcdcaps1]

Re: GNR TS902W no power , help please

Attached are photos of My LCD Monitor Power board

[lcdcaps1]

Re: GNR TS902W no power , help please

Hi
Yes in EU-UK
240V AC

Stuck on what next to do
checked fuses and zero ohm resistors again

[rddube]

Re: GNR TS902W no power , help please

Sorry for asking again, but can you post clear large photos of both sides of your power board, we can then help you diagnose the problem.

If you measure 324V on the big cap (be careful when measuring on the hot side of the power supply), are you in Europe?