Hanns-G HG281D, LCD Monitor no power

[akajoshx1]

Re: Hanns-G HG281D, LCD Monitor no power

I have a problem with this monitor where it takes about 50 tries to get it to turn on. Once it is on everything works perfectly. Is there a good way to test the power supply board? I would like to plug in the AC power and turn on the board without using the monitor's power button. I see that in the back there's a printout that says PSON so I wonder if I can use that some how to turn the board on. Let me know of any suggestion. Thanks.

how did you solve this problem?
I have to literally press the power button 100 times for me to get the monitor to turn on. ironically the monitor turns off in one button press. I have ruled out a faulty switch by replacing the menu switch with the power switch.

When the monitor is on, it works flawlessly. But once i turn it off , it will sometimes take a 1000 power button press to turn on. on a lucky day i can get it to turn on after 2 or 3 presses.
HELP!

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

So today I recapped all the capacitors form the power board excluding those from underneath of the heat-sink (near the PFC Choke). So now I have 5Vstd-By with no ripple, but then I tried to start the main power supply It won't start. After that I replaced the optocoupler, now It tries to power, I measured 16V and 36V instead of 12V and 24V. The 5V rail seems to be stabile but it comes from a buck converter.....so it has it's own feedback..... I have also find that the power to the resonant controller is 16V from datasheet this is too much.Now taking into account that the 5VSTD-By supply it has 5V, why the resonant controller for the power board has 16V? those are all powered from the std-by supply, no?

Le update.....
Now I think the L6598 is toasted, no start at all and it has 16V across it.

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Have you replaced the 2 caps on the main board?
The 12v and 24v are probably not regulated so as the back lights are not lit the voltages will be higher. Check the battery in your meter is not going flat.
Did you try the jump with a resistor and main disconnected?

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

Have you replaced the 2 caps on the main board?
The 12v and 24v are probably not regulated so as the back lights are not lit the voltages will be higher. Check the battery in your meter is not going flat.
Did you try the jump with a resistor and main disconnected?

Yes it was started with a resistor, main disconnected (caps replaced on the main) the problem is with the higher voltage applied to the resonant controller , 16V instead of 13-14V....

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

What is the part number of the controller -
did the lights flash at all when you jump started it.
Have we any pictures of your boards - might help

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

What is the part number of the controller -
did the lights flash at all when you jump started it.
Have we any pictures of your boards - might help

It's L6598, Like I said.....it was only the power supply , and a 12V 40W bulb.

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Your losing me now. You were asked to do the jump start with it all connected except the
main board. Budm asked you to check if the pfc was working when it was jump started by measuring the voltage at the BIG cap.
I thought L6598 was a board number so a coil - hence the request for pictures.
Which pin on the L6598 are you reading the 16v on?

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

5V STBY power supply is the its own power supply, the aux winding of the stby supply is used for supplying the B+ to run the PFC IC, 12V/24V SMPS IC. Pictures of the board and the parts you replaced. The12v/24 volt are too high can be due to its regulation feed back is bad. Did you match the spec of the opto? it is part for regulation circuit.

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

5V STBY power supply is the its own power supply, the aux winding of the stby supply is used for supplying the B+ to run the PFC IC, 12V/24V SMPS IC. Pictures of the board and the parts you replaced. The12v/24 volt are too high can be due to its regulation feed back is bad. Did you match the spec of the opto? it is part for regulation circuit.

I have replaced all 3 opto, they were cooked (the board has discoloration under and near them). The were replaced with the same part number Sharp PC817.
Taking into account that the 5V std-by and the PS-on are working it means that the opto's are ok. I looked at oscilloscope waveform and now it's runing at almost 1.2Mhz (the IC for the 24/12V was powered from a laboratory power supply 13V without the high voltage to the Fets/PFC, only power to the IC.).
So I guess that I need to replace it, maybe the 16V were too much for it (has an internal clamping and I think it did dissipate some power).

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

How do you hook up the scope ground? Using the chassis? 1.2MHZ? I do not think so. You know about safety when working in the primary side and how to take measurement? Opto barely dissipates any power, it just have LED and Opto transisor inside.

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

How do you hook up the scope ground? Using the chassis? 1.2MHZ? I do not think so. You know about safety when working in the primary side and how to take measurement? Opto barely dissipates any power, it just have LED and Opto transisor inside.

Does anyone read what I'm writing???? It was powered from a laboratory power supply! And to be more exact It's a Fluke Scopometer powered from battery. Yes I'm an engineer, I know how to work with it. Anyway with the new opto it engages power for the IC....
Yes 1.2Mhz, I didn't say that the signal looks good, but it is from 0.74 to 1.2Mhz, so I'm telling that the IC is toasted.
Anyway thanks, I will change it and hope it will start.

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

Yes I did, using external supply to supply b+to the SMPS IC does not isolate he primary circuit ground from the scope ground since scope ground is tied to the chassis safety ground. The negative leg of the main 450vdc filter cap is the primary side ground ref point. If you attach the ground probe to that primary ground ref, you will get big spark unless you use isolation transformer on the the power supply or use Differential probe for your scope.
3 opto, one for 5vstby, one for 12v/24v , one for PS_ON. We still do not know if the pfc is working either.
"without the high voltage to the Fets/PFC" so the power MOSFETs for driving the 12v/24vtransformer are not being supply with 380VDC then since PFC is not working.

[Hellofly]

Re: Hanns-G HG281D, LCD Monitor no power

Hi all,

Another owner of Hanns- HG281D failing and hope to get some help to get it going again. My monitor have no problem power on, but after power on the image on the screen show up normal for about 2 seconds then the screen start to fade and change the color, the image on screen turned very bright and then slowly fade and become negative just like how negative 35mm film are and remain that way. Power off and on the monitor will behave the same way. After reading through this thread, I have try to replace a few caps on the main board (C80, C83 and other 16V 100uF) even though none of them physically look bad. Replacing those caps on the main board doesn't seem to fix the problem. I will possibly tackle the power board next, but before that I wonder anyone else have seen this problem on this monitor? Any help/info is appreciated.

Thanks

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

You should use good make low esr caps - Panasonic FR FM or FC not something from radioshack.

Hellofly - hopefully you read this?

perhaps update your profile with country and mains voltage.


EDIT

Also you did put them in the right way round?

[Davi.p]

Re: Hanns-G HG281D, LCD Monitor no power

Budm: CATA has said that its scope tests are made without mains plugged in to monitor, no high voltage in, only external power to smps ic and scope connected, so there's no need of isolation transformer.

akajosh: You have to open the monitor and test the voltage on bigger capacitor (very carefully, i suggest you try to found one way to test it from the upperside) and then test the psu outputs, test also the smps ic (sorry i don't have read the part no.) vcc pin.

NOTE:
I don't know why no one here have never thinked to post a sticky note where it says to not put himself in queue to others thread especially if monitor or sympthoms are different, in Italian forum this is severely prohibited, one cannot read 500 posts to arrive to the finals or he doesn't know from where start to read. Thanks..

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

"Budm: CATA has said that its scope tests are made without mains plugged in to monitor, no high voltage in, only external power to smps ic and scope connected, so there's no need of isolation transformer." I know, but since you are running it without having feed back from the output section, the test is not valid, and also there is nothing in the circuit to generate "Yes 1.2Mhz, I didn't say that the signal looks good, but it is from 0.74 to 1.2Mhz," 740KHz~1.2MHz even if he is looking at the harmonics (which you cannot see only the harmonics without see the fundamental freq.) of the SMPS main frequency which will be less than 100KHz.

[Hellofly]

Re: Hanns-G HG281D, LCD Monitor no power

Hellofly - hopefully you read this?

perhaps update your profile with country and mains voltage.


EDIT

Also you did put them in the right way round?

Hi selldoor, thanks for response.

I did not order capacitors from online, perhaps I got the capacitors from a local electronic shop, the capacitors are NTE brand. I don't know how good they are compare to Panasonic capacitors.

I have update country and mains voltage. I also did confirm that i did put them in the correct polarity.

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

NTE caps are not suitable - may even be worse than what was in - you should get
Panasonic FR FM Or FC

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

Can someone provide me the values of R128 and R124?

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Which board are they on - are they standard or smd do they have any marking on them