Hanns-G HG281D, LCD Monitor no power

[rector]

Re: Hanns-G HG281D, LCD Monitor no power

notablemusician see post #39

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Rector - are you saying you did not test the inverters?

No power to boards- meter on ohms 2000 test across the two pins of each transformer on the the top -in your picture.

[MGMCCALLEY]

Re: Hanns-G HG281D, LCD Monitor no power

Use this one:
http://www.digikey.com/product-searc...=0&pageSize=25

Budm,

THANK YOU SO MUCH! Those were the exact caps I needed. The monitor is officially repaired, and has been going strong for over 3 weeks with absolutely no issues. Apparently I have the ultimate power supply, because none of those caps were bad at all. My blanking problem was just those few caps on the motherboard, nothing more. And now I have a revived 28" monitor. You the man, Budm, you the man.

-MGMCCALLEY

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

Glad to hear!

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

Hello,
I have also a problem with this monitor, for the moment I didn't replace the capacitors, The 5V Stb By is working.
How can I turn on the PSU without the other board? Connect the PSUON to the 5v std-by? Also the q601 seems to be very toasted but the junction diode is ok, i would replace it, but I don't know it's part number. Can someone tell me an alternative to that? Also without any connector, and the mains ON on the middle octocoupler (hot side) I have 22V, I guess that one is responsible for start-up ? (With 5v on psuon?)
BTW myne is the one with PFC.

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Read the thread again - replace caps on main board c80 & C83

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

Read the thread again - replace caps on main board c80 & C83

Dude, those capacitors are for the logic board, I asked about the PSON???
Meanwhile I repaired the std-by power, not it has 4.99V.
For the moment I have some improvement, the led is powering from blue to yellow.
I see that seccond power supply it doesn't start, so I asking is the middle octocoupler responsable for the power Up?
I see that the octocoupler led has around 1.2V and on the fototransistor 22-27V
Also on the capacitors C83-80 I have 3.3V and 2.2(off)and 1.8V (on state), I guess that these voltages are from the std-bu power supply.

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

You should have stable 3.3V and 1.8V all the time.
https://www.badcaps.net/forum/showth...ghlight=HG281D
http://s807.photobucket.com/user/bud...ml?sort=3&o=12

So you do not get the 24V when force on the PS_ON PIN? Also check to see if the PFC Voltage booster circuit is working or not, the voltage on the main filter cap should go from 330V to around 370~390VDC when PS _ON is applied.

[sirpouralot]

Re: Hanns-G HG281D, LCD Monitor no power

First time poster here.
Wanted to thank you all for the help. Only had to replace C83 and problem fixed. Mine had a blinking problem when coming out of standby. It would come out ok, and then in about 5 to 10 seconds it would go black for a few seconds and then come back on again. It would repeat this several times before finally staying on.
Once on, it would be fine until next time it had to come out of standby.
Seemed to be getting worse.

Un soldering 83 was a lot harder than removing the capacitors on the mother boards that I practiced on.

I did have a question.
the capacitor I used to repair was one I took out of an old motherboard. It had the right numbers on it. 100 and 16v
It was the same diameter, but only about half the length. Real small.

Will this one be short lived since it is kind of small. I had another one that came off the same motherboard with the right numbers on it, but it was much bigger than the original. I just didn't have enough room to use that one. the leads were a little wider also.

No more blinking for now which is great. I did manage to burn the tip of my ring finger with the soldering gun. Ouch!!

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

I would replace both of them and they have to be low ESR type. When you try to remove part from PCB, you should use 45~60W Iron and always add more solder and flux to the both joints of the cap's legs, move the soldering tip back and forth between the twp legs while pulling out the cap.

[sirpouralot]

Re: Hanns-G HG281D, LCD Monitor no power

Pretty sure the cap would be low ESR.
From about 2007 it became common for better-quality computer motherboards to use only polymer capacitors where wet electrolytics had been used previously. I am just not sure about the smaller physical size of the capacitor. This one was real small. I didn't replace C80 because I had such a hard time with 83 that I was pretty sure I had destroyed the board already.

After discovering it solved the blinking problem, I think I will wait to see if any further problems develop before attempting another repair.

I also just noticed I ended up with a strip of foil that is about 2" wide and 10" long. It must have been wrapped around some wiring, but I can't remember where it is supposed to go. Anyone remember? Not sure what it was for, perhaps electrical noise insulation?

[Lumberjack777]

Re: Hanns-G HG281D, LCD Monitor no power

Ok, here's the deal. "If it ain't broke, don't fix it" my Grandpa used to say. You could make matters worse.
That main board is "through hole soldering" - and it's a whole different animal. Like budm says you have to have a very hot iron, add more solder at first; then touch each joint (back and forth) and wiggle the cap out. Then you have to clear out the holes. I think budm and retiredcaps use a stainless steel dental pick to clear the holes. My method is to add some solder to make a little mound. Put a dab of flux on it. Then cover it with fresh solder wick and hit it with a hot iron. If you do it just right, you'll vacuum out the entire hole. I should probably use a dental pick, but I'm too cheap to buy one

The "strip of foil" is aluminum tape and it was on the metal shield that covers the PSU and main board. You don't have to worry about that it you already have it assembled.

NOW......for the future......that smaller cap might well give out someday soon. You want to watch for any sort of peculiarities in the image. Fuzziness, waves, dots, sparkles, anything unusual. Then you want to get those 2 caps. From like Digikey. Probably cost you all of 5 bucks including shipping. Then replace them both proper. Then you'll be good for a long time. There is a possibility that if you waited too long, you could take out a voltage regulator. So I'd pass along to you, the advice my Grandpa gave me - "if it ain't broke, don't fix it" - but if it starts to get broke. Better fix it

[sirpouralot]

Re: Hanns-G HG281D, LCD Monitor no power

Ok thanks a bunch. I will order both capacitors but probably only replace the one I just did for now since that solved my problem. That one will be easy to get back out.
It doesn't take long to take the monitor apart once you have done it. That through hole sucking the solder out is very difficult. I couldn't get anywhere with the normal soldering pencil, so I picked up a de-soldering tool with a turkey baster attached to it. The tip is hollow and fits neatly right over the soldering joint.
You would think that would be enough, but not even close. I did the add a little solder trick and then worked back and forth between the two pins while wiggling it. The thing gets loose but just won't pull out, It soon gets so hot you can't hold on to it. Once you let go and take the heat away, it just firms back up. When I finally got the thing out, I noticed the hole had closed back up.
I ended up taking one of the larger capacitors I had laying in my bin and bent one of the wires back so I could just use the one to push with. I then applied the heat from the other side and managed to work the solder out of the hole. Next time I think I will use a paper clip as I almost ended up getting the thing stuck instead of clearing the hole. I read somewhere that solder won't stick to a paper clip.
I would have just replaced the board, but I couldn't find any available anywhere except China and I wasn't taking a chance on that ever arriving for $75.00 by the time you pay shipping.
It is hard to believe with as much heat and solder spatter that the thing works at all much less solved the problem, but 83 was the right capacitor. I just hope 80 will hang on.
Thanks for the help.
This site is great.

[CATA2003]

Re: Hanns-G HG281D, LCD Monitor no power

You should have stable 3.3V and 1.8V all the time.
https://www.badcaps.net/forum/showth...ghlight=HG281D
http://s807.photobucket.com/user/bud...ml?sort=3&o=12

So you do not get the 24V when force on the PS_ON PIN? Also check to see if the PFC Voltage booster circuit is working or not, the voltage on the main filter cap should go from 330V to around 370~390VDC when PS _ON is applied.

Ok, so the PSUON should be pulled to the 5V STD-By?
This week I will replace all the capacitors.

[selldoor]

Re: Hanns-G HG281D, LCD Monitor no power

Ok, so the PSUON should be pulled to the 5V STD-By?
This week I will replace all the capacitors.

You can disconnect the main board from the power supply and try and jump start it with a 1K resistor from the 5v to the PSon. Back lights may light up
but nothing else will come on screen

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

To force on the stand alone power supply, use 1K resistor between PS_ON and 5VSTBY as Selldoor suggested, to force the backlights to come on you will also need resistor between BL_ON (INVR_ON) and 5VSTBY, some design may also needs 1K between DIM and 5VSTBY for the backlights to stay on.
You can also check the voltage on the PS_ON, BL_ON pins to see if the main board is sending the signals or not (you should have the monitor connected to running PC).

[BrownSystems]

Re: Hanns-G HG281D, LCD Monitor no power

First time poster. Thank you already. This forum has a wealth of information.

First time poster here.
Mine had a blinking problem when coming out of standby. It would come out ok, and then in about 5 to 10 seconds it would go black for a few seconds and then come back on again. It would repeat this several times before finally staying on.
Once on, it would be fine until next time it had to come out of standby.
Seemed to be getting worse.

This describes my issue exactly. To add to this, I noticed mine will actually work fine if I reduce the resolution to 800 x 600. The screen will eventually come on and work find but always has a problem after coming out of stand by.

Should I assume my problem is the same capacitor? Which board is this capacitor on?

Admittedly I have yet to solder anything but have been researching repairing monitors for some time. I have considered going all in and getting some good soldering gear to fix my own electronics from here on out. Any words of advice?

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

That will be the two caps on the logic board., 100uf 16vdc, C80, 83
https://www.badcaps.net/forum/showth...ghlight=HG281D
But you should also replace a set of caps in the power supply board also.

[BrownSystems]

Re: Hanns-G HG281D, LCD Monitor no power

Thanks. Supposedly the entire PSU was replaced by the person I purchased it from so hopefully that part is good.

[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.