Hanns G HG281D Blacklight fails after warming up.

[Tyradius]

Hello all. I have been reading these forums for awhile now but have yet to post until now!

I have a hanns g HG281D monitor that started having problems awhile ago. It started much like others on this forums have. The power button wouldnt turn the monitor on, having to press it 20-30 times before it would finally come on. Once it did come on artifacting could be seen randomly on the screen.

Eventually it stopped powering on all together and I let it sit and used my tv as a monitor. Well yesterday I finally decided to fix it. I took it all the way apart and completely replaced all the capacitors on both the psu and main board (all except the filter cap). When I was done the monitor powered up and started working fine (after I took it apart and found a loose cable causing the video to be grainy). Everything seemed fine and so I decided to watch some youtube videos to let it burn in.

Well I didnt even get 30 seconds into the video when the monitors backlights started shuting off then coming back on. It did this about 4-5 times before the backlight shut off and did not turn back on.

Turning the monitor off and waiting for about 5 minutes and turning it back on it came right back up again. Then after 4-5 minutes the backlights turned back off again.

I do not have a multimeter at the moment. I ordered one from amazon but I havent recieved it yet.

I was just wondering if anybody with experience could point me to some possible items to check?

I plan on double checking all of my solder points but I was wondering if anything else could be causing this?

It seems to me that when the components heat up there must be some kind of expansion happening? Causing some kind of short or improper connection?

I have some pictures of the PSU below, before I changed the capacitors. Sorry for the picture quality, I only have a 5mp camera on my cell phone.Plus having to reduce the size and quality in order to upload them didnt help either. Also one picture I took after getting it up and running, before the backlights went out. I thought I had taken pictures of the Mainboard but I guess I didnt! I will get a few snaps of that soon!

All the replacement capacitors are Panasonic and Nichicons.

I hope you guys can help me! and sorry for the long post

[PlainBill]

Re: Hanns G HG281D Blacklight fails after warming up.

There is no problem with the quality of the pictures. A 5 Mp cell phone camera is more than adequate provided the lighting is good. My guideline is simple - if I can read the component identifiers, the pictures are good enough.

There are a few pieces of information that are missing.

1. What was the series' of Panasonic and Nichicon caps used?

2. Does the power light go off when the backlights go off?

3. A picture of the inverter may be helpful. If my memory serves, the caps on the inverter can also cause problems.

PlainBill

[Tyradius]

Re: Hanns G HG281D Blacklight fails after warming up.

1. The series were mainly Panasonic FC and Nichicon PW but a few were Nichicon HE series and the 10v 1000uf caps were KY. The 10uf 35v , 10uf 16v , and 100uf 16v caps were Panasonic GA and the large 22uf 400v was a panasonic CE.

2. No the power light stays on.
The caps on the inverter are green, I cant read the manufacturer only the last part says CON they say EVL on the side and are 100uf 35v caps. I have Nichicon 100uf 35v's in PW. I removed one of the caps to get the specs on it and tested with an ESR meter. It showed as .09 on the meter, I probably jumped the gun a bit but I went ahead and replaced all the caps on the inverter. The monitor still does the same thing.

3. I should be able to get some pictures later. I touched up all of the solder joins on the main board. This did not seem to help. Im starting to think its more then just bad caps. But I will let people with more experience working with monitors be the judge of that.


edit: Ok after I posted that I tested the monitor again. It came on for around 10 seconds before the backlight went off. But the entire time the blue power light was flickering. It was not doing that before.

[PlainBill]

Re: Hanns G HG281D Blacklight fails after warming up.

Let me recite my usual spiel. This APPEARS to be a case of 'two seconds to black'. Two seconds to black can be caused by bad capacitors, a bad transformer, bad CCFLs or the wiring to the CCFLs, or a bad component in the protection circuit.

I feel you have eliminated the capacitors as a possible cause. The next easy step is to compare the resistances of the secondaries of the inverter transformers. These should match to within 3%. If you need guidance, a picture of the inverter will be necessary.

The easiest way to check the CCFLs and wiring is to substitute a known good CCFL (it can be in another panel, no need to remove it from the panel) for each CCFL in this monitor. If the problem goes away when one CCFL is replaced, you have identified the bad CCFL.

PlainBill

[Tyradius]

Re: Hanns G HG281D Blacklight fails after warming up.

Ok, so since my last post I re re did the solder joints. This time I also touched up the joints for the cable plug ins, as well as a through hole chip on the logic board.

I also decided to blow the logic board off with a compressor. Why might you ask? Well when I was desoldering the old caps off I had a hell of a time getting the solder out of the negative holes for the caps. So I used a very small drill bit the size of the hole, and a hand drill to clear the holes. I thought I had blown any potential solder bits off using the power of my lungs.

In the end the display was running for several hours with no problems visually.

However a new problem that wasnt there before has emerged. When I hit the button for menu, the screen shuts off, and you can hear the speakers giving a static hissing like noise for a second.

I am going to have to take it apart again and see if I might have bridged some pins when I re soldered them.

This has been a great learning experience. I dont know if there were pieces of metal causing shorts, or if re doing the solder connections helped, but im one step closer to a working monitor.

[jetadm123]

Re: Hanns G HG281D Blacklight fails after warming up.

If possible, try re-seating the ribbon cable between the pushbutton and logic boards. Also, carefully look at the two boards as you may have blown some of the solder shavings onto them.

[Tyradius]

Re: Hanns G HG281D Blacklight fails after warming up.

Thanks for the suggestions. I will look into that. And thank you plainbill for all of your help. I have around 15 monitors here at work I want to try and fix. I hope to learn a lot from you and others in the future!

[Tyradius]

Re: Hanns G HG281D Blacklight fails after warming up.

So I won an auction for another hg281d on ebay, it arrived today. I was able to use its parts to figure out what the issue is.

It seems I messed up something on my logic board, which is causing the screen to quickly flash auto adjust over and over when you hit the menu button. The new monitor had the same symptoms as my old. After a complete recap, and being very careful with the logic board, that monitor works 100%.

So I now have one monitor thats 100% and the other works just fine but doesnt have a menu button.

I am going to see if I can find a logic board online, I think its one of the ic's that I may have overheated when soldering.

Thanks for the help!