Hanns-G HG281D, LCD Monitor no power

[Mishannya]

Hi all, I have Hanns-G HG281D LCD monitor with no power problem.
I inspected visually all caps on PS board (PSM217-404-H-R), they are look absolutely normal. Also I tested all big semiconductors, fuses, coils, transformers and resistors. Nothing found bad so far. If some body had similar problem with this issue please help. Thanks.

[retiredcaps]

Originally Posted by Mishannya

If some body had similar problem with this issue please help.

1) Does the power LED come on at all or stay off?

2) If you have a multimeter, check the secondary voltages on the connector between the power board and logic card. You should get 5V DC at least one of the pins.

3) Post clear focused pictures AFTER reading

http://www.badcaps.net/forum/showthread.php?t=1868

4) Please do not post pictures inline.

5) Take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focus pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

6) Here is an example of the pictures we want.

http://www.badcaps.net/forum/showpos...94&postcount=1

[Mishannya]

Q: 1) Does the power LED come on at all or stay off?
A: No, it doesn't.
Q: 2) If you have a multimeter, check the secondary voltages on the connector between the power board and logic card. You should get 5V DC at least one of the pins.
A: The 5V DC presents on the power board and logic card (actually 4.4V ~ 4.9V DC)
Thanks.

[retiredcaps]

Originally Posted by Mishannya

A: The 5V DC presents on the power board and logic card (actually 4.4V ~ 4.9V DC)

Good photos.

Regarding the 4.4 ~ 4.9V DC, is that fluctuating or do you mean one pin is 4.4V and another is 4.9V DC. 4.4V DC is low and is suspect.

On CN7, do you see 12V DC? The picture of the logic board shows 12V DC printed on the PCB.

[Mishannya]

4.4 ~ 4.9V DC, is fluctuating on CN5 of the logic board.
And there is no 12V DC On CN7.

[retiredcaps]

Originally Posted by Mishannya

4.4 ~ 4.9V DC, is fluctuating on CN5 of the logic board.
And there is no 12V DC On CN7.

If the voltage is fluctuating, that could suggest bad capacitors. Capacitors don't have to bloat in order to be bad. They can be out of uF spec or have high ESR (ohm).

The heat shield makes it difficult to see, but you can try measuring the voltage across the capacitors that are on the 5V rail. Any cap that is 10V or less is probably on the 5V rail.

You can probably trace CN5 to the caps that feed it the 5V DC.

[Mishannya]

I'll test all caps by ESR meter tomorrow. Thanks.

[retiredcaps]

Originally Posted by Mishannya

I'll test all caps by ESR meter tomorrow. Thanks.

What DC Voltage do you get across the main filter capacitor? It should be a steady mains * 1.4. Be careful measuring this voltage.

[Mishannya]

168V DC across the main filter capacitor.

[retiredcaps]

Originally Posted by Mishannya

168V DC across the main filter capacitor.

Okay, that is good. Post your results for the ESR tests tomorrow. You may want to measure the capacitance of the caps as well.

[seanc]

It could be a trick of the light, but it looks like one of the caps has a slight bulge under that heatsink.

[retiredcaps]

Originally Posted by Mishannya

4.4 ~ 4.9V DC, is fluctuating on CN5 of the logic board.
And there is no 12V DC On CN7.

Odd, on the back of the power board, there are markings for 5VSB, 5V, and 12V.

On the backside, there should be a multi legged IC that is the SMPS or PWC controller. I can't make out the part numbers, but can you list

U101, U501, U801, U102, and U202?

[Mishannya]

U101-L6562D, U501-3037CS, U801-LM324DG, U102-L6598D,
and U202-LMC555CM.

[momaka]

U7 on the video board looks very discolored. Check the DC voltage on it with your multimeter by placing the negative probe on ground and the positive probe on the tab of U7. It's probably a 3.3v regulator. Also check the DC voltage on U8, same way as for U7. Post what voltages you get.

[Mishannya]

U7 reads (2.9V~3.3V), U8 (1.6~1.8)

[jetadm123]

Nice photos! If you look at your second photo, at the lower left , you'll see voltages silk- screened on the board: 5V, 12V and 24V. You've verified the 5V, but not the 12V and 24V, You'll have to trace these outputs back to the duo diode paks mounted on the heatsink. Lack of 12V and 24V can be caused by a blown fuse, bad filter caps or bad duo-diode paks.

Also, in the second photo, did you check Q501 and Q502 for shorts? What are their part numbers?

A photo of the entire power/inverter board with the heatsink covers off would be nice.

[retiredcaps]

Originally Posted by Mishannya

U101-L6562D, U501-3037CS, U801-LM324DG, U102-L6598D,
and U202-LMC555CM.

3037CS is the PWM controller. The datasheet is at

http://pdf1.alldatasheet.com/datashe...IRU3037CS.html

Download and save for future reference so we can verify the correct voltages.

[retiredcaps]

Originally Posted by Mishannya

U7 reads (2.9V~3.3V), U8 (1.6~1.8)

The fluctuation is not good. It should be a solid 3.3V and 1.8V DC.

[retiredcaps]

Originally Posted by jetadm123

You'll have to trace these outputs back to the duo diode paks mounted on the heatsink.

If the duo diode voltages are fluctuating as well, I believe it could pointing to a bad transformer or a bad PWM controller.

If the duo diode voltages are solid 5V, 12V DC, etc, then it is likely bad caps causing the fluctuations at the connectors.

PS. What type of multimeter brand and model number do you have?

[retiredcaps]

Just thinking about this a little bit more, I think based on the fluctuating 4.4 to 4.9V DC, that is probably on the 5V SB standby rail. So on the solder side, trace where the 5V SB goes to and test those caps.

So focus on the getting stable 5V SB voltage first and foremost.