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).
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).
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).
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.
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
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.
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.
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.
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.
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.
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.
Ok, so if you have no voltage at the startup cap, that means that something before it is not working.
However, what are you using as ground to measure voltage on the startup cap? Your best ground on the hot side of the power supply is the negative side of that big main cap. Again just to make sure, be very careful in that area because you are playing with 324 V.
Can you take a photo of the section I highlighted in blue without the glare hi-res?
You'll have to trace the + side of the startup cap to see what is not delivering voltage. I marked the + side of the startup cap in the photo.
Also could you check L103. Check voltage on each side or resistance of L103.
Ok so I measured the voltage on the startup cap as you suggested using the ground/negative from the main cap and i get nothing
I am considering to replace the startup cap
as the esr is out of spec
I tested the power mosfets and they seem ok
I tested L103 and i got 318 V on both sides
Attached are photos from the back, I am using the highest setting on camera and took a few shots
Hope they are ok
Ok, so if you have no voltage at the startup cap, that means that something before it is not working.
However, what are you using as ground to measure voltage on the startup cap? Your best ground on the hot side of the power supply is the negative side of that big main cap. Again just to make sure, be very careful in that area because you are playing with 324 V.
Can you take a photo of the section I highlighted in blue without the glare hi-res?
You'll have to trace the + side of the startup cap to see what is not delivering voltage. I marked the + side of the startup cap in the photo.
Also could you check L103. Check voltage on each side or resistance of L103.
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.
Ok, check J101 and J102 for resistance they should have no resistance (they are fusible resistors). Also, check i you have any voltage (again be careful) at any of the 3 pins of the mosfet (or transistor) mounted on the heat sink.
Could you also tell us what is the markings on U100?
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