Monitor won't switch on, with a click sound on the board!

Hey everyone,

I need some help troubleshooting an issue with my monitor, and I could really use your expertise. Unlike others with the same monitor, mine doesn't have any backlight. I've already checked the fuses and visually inspected the boards for any signs of burned capacitors, ceramics, or other obvious problems, but everything looks fine.

I decided to test the power supply unit (PSU) separately, and it doesn't seem to be outputting any current through the plug. I've measured each pin individually, but I haven't detected any current on the output. The main capacitor and all the medium-sized ones are holding a charge, although I haven't removed them from the PCB, so I'm not sure if my measurements are accurate.

Here's where things get interesting. When I plug the PSU back into the main board, I hear a faint clicking sound coming from one of the boards. I can't pinpoint exactly which one it's coming from, but the rhythm of the clicks is around 90 beats per minute. This makes me think that there might be a faulty capacitor somewhere that isn't burned, but isn't functioning properly either.

I have the necessary tools for soldering, such as iron and some soldering skills, as well as a multimeter for measurements. Unfortunately, I don't have access to an oscilloscope. While I could simply order new boards, I live in Vietnam, so options like eBay and Alibaba aren't available to me. If I can identify the specific component that's broken or burned, I believe I can find a replacement and fix it, rather than replacing the entire set of boards.

I'm determined to tackle this issue, but I'm not sure where to start. If anyone has any insights or if the clicking sound gives you any ideas about a direction to follow, I would greatly appreciate your input.

Cheers!

@oldturkey03 narrowed down the sound to an area but I can't be sure 100%

I think the sound is coming from one of these 3 components - but keep in mind that the card doesn't make a sound if not connected to the rest of the boards (somehow).

This is the side missing - I shunted it before I got the multimeter and the fuse just in case. but I will remove the shunt later.

Thank's a lot for helping out - I wish I could help the community more but my skills are mainly handcraft based - I was working for Airbus and Thales at some point in my life. But I was mainly following schematics and soldering on binocular prototypes... so my electronic knowledge is basically U = I*R

For the measurement of the plugs, I tried between black wire to all the colours without reading.
when I did measure between the caps in the red square I had oscillating readings (I'm using an old-school multimeter).

Cheers!

@oldturkey03 so I did just that. measuring between fuse and ground. I do have some voltage but its really small and it also oscillates at less than 0.5v

I have also measured the big cap 450v/100uf and its reading is pretty low too if it is supposed to be at 450v it's now at 255 and fluctuating.

On this image
Red arrow big cap = 255V (oscillates)
Green arrow small cap = 4.5v (stable)

White arrow = 0.3v (oscillates)

Purple and pink Purple is the GND and coloured ones have the same voltage = 0.3v (oscillates)

the test you asked for also shows 0.3v (oscillates).

in addition, I just made another test. I remove the rest of the cards I was wondering if unconnected the Psu card would still have the same reading- so first the Psu card alone does not click.

I made the same test as above and the readings are now better 450v on the big cap with no oscillation - 4.5v on the green arrow - when I measure the pins on the connector from purple to all the colours I have now higher voltages around 20v with no oscillation.

So I turned then I unplug the Led card from the main and plugged the main board back into its PSU magic the click is back and so are the low voltages. On the right side of the main board, the caps did retain voltages but on the left side they didn't (measured the big caps none of the ceramics SMC) so I kind of want to replace them since I have no way to test them my multimeter doesn't measure capacitors, it's only 3 guys to order before I give up and try to find a replacement card that can be shipped in Vietnam which is probably impossible...

You said earlier that maybe the PSU is sleeping when nothing is connected to it, and I have 2 pins white and grey that never showed any voltages should I try to short them to see if the click comes back?