Hanns-G hg281d bright band

[cammac725]

hi-

I have a 28" HannsG hg281d LCD monitor that works fine for the first 5 minutes of operation. Then it starts showing the bottom third of the display as a brighter band. The image is still visible, no wavy at all, just brighter. It will stay like this until shut off.

It will do it using HDMI or D-sub and I have tried known good cables and 3 different computers and it always does it.

I don't think it is the caps or backlight bulbs, in my limited experience. Someone mentioned the horizontal transistor or flyback transistor. Does this sound reasonable?

This is a friend's monitor and the brightness was set to 60 so I don't think it has overheated. I opened it up and I see nothing wrong upon a cursory inspection of the boards.

I would love it if someone could point me in a direction!

Thanks

I've attached a pic of the problem.

[jetadm123]

Re: Hanns-G hg281d bright band

Please post some good clear focused photos of the entire power supply board top and bottom. Also a photo of the logic board would be good. Do not post your photos inline. Please use the "manage attachments" button.

[PlainBill]

Re: Hanns-G hg281d bright band

hi-

I have a 28" HannsG hg281d LCD monitor that works fine for the first 5 minutes of operation. Then it starts showing the bottom third of the display as a brighter band. The image is still visible, no wavy at all, just brighter. It will stay like this until shut off.

It will do it using HDMI or D-sub and I have tried known good cables and 3 different computers and it always does it.

I don't think it is the caps or backlight bulbs, in my limited experience. Someone mentioned the horizontal transistor or flyback transistor. Does this sound reasonable?

This is a friend's monitor and the brightness was set to 60 so I don't think it has overheated. I opened it up and I see nothing wrong upon a cursory inspection of the boards.

I would love it if someone could point me in a direction!

Thanks

I've attached a pic of the problem.

So someone suggested the flyback transistor? That person is either dishonest or an idiot.

I'd suspect the panel card, although at 28" this might have a tcon. As already suggested, pictures will be needed.

PlainBill

[cammac725]

Re: Hanns-G hg281d bright band

I had to wait quite a while because after reassembly, the problem didn't start happening for about 1 hour, then started flickering (only the bright band) and showing lines, then would go away for up to an hour.

So someone suggested the flyback transistor? That person is either dishonest or an idiot.

PlainBill

Probably closer to the latter, or just trying to act like he knew something, tossing around component names.

I've attached photos of all the boards except the inverter board...and it may show the problem. I hadn't looked at the flip side of the board with the input jacks. It looks like lots of corrosion(?)...none of the solder joints are shiny. None of the other boards show that, nor do any of the connector pins.

The metal plate that is still on the power board is soldered to the board so I left it on for now. I can remove it if anyone wants to see underneath.

Hopefully the photos are adequate; I pulled out my tripod for these.

Thanks

[PlainBill]

Re: Hanns-G hg281d bright band

I had to wait quite a while because after reassembly, the problem didn't start happening for about 1 hour, then started flickering (only the bright band) and showing lines, then would go away for up to an hour.



Probably closer to the latter, or just trying to act like he knew something, tossing around component names.

I've attached photos of all the boards except the inverter board...and it may show the problem. I hadn't looked at the flip side of the board with the input jacks. It looks like lots of corrosion(?)...none of the solder joints are shiny. None of the other boards show that, nor do any of the connector pins.

The metal plate that is still on the power board is soldered to the board so I left it on for now. I can remove it if anyone wants to see underneath.

Hopefully the photos are adequate; I pulled out my tripod for these.

Thanks

Excellent pictures. The power supply looks quite clean at first glance. There are a couple of points on the other boards that bear checking.

On the signal (logic) card U7 and U8 are respectively the 3.3V and 1.8V LDO regulators. Measure the output voltage of each; use the ground ring around the mounting hole just to the left of U8.

On the panel card U404 and U406 are two more regulators They conveniently labeled the input and outputs. Also, U200 is the voltage regulator for the panel itself.

PlainBill

[cammac725]

Re: Hanns-G hg281d bright band

I just love an intermittent problem, especially when I barely have time to get my leads in place and the problem goes away.

U7 has 3.28v in, 1.53 out
U8 has 1.77v in, 1.49 out
U404 has 4.60 in, 3.31 out
U406 has 3.30 in, 1.79 out

None of these values changes when the display has the bright band.

I'm not sure how to test U200. Man, that thing is tiny.

I might see if I can redo some of the more blemished solder points on the back of the signal board.

cammac

[PlainBill]

Re: Hanns-G hg281d bright band

I just love an intermittent problem, especially when I barely have time to get my leads in place and the problem goes away.

U7 has 3.28v in, 1.53 out
U8 has 1.77v in, 1.49 out
U404 has 4.60 in, 3.31 out
U406 has 3.30 in, 1.79 out

None of these values changes when the display has the bright band.

I'm not sure how to test U200. Man, that thing is tiny.

I might see if I can redo some of the more blemished solder points on the back of the signal board.

cammac

Look up the datasheet for it. It produces the voltages necessary for the proper operation of the LCD. If the output voltages are stable, it's not the problem.

I've got to say, the odds are it's the LCD panel itself.

PlainBill

[pedro]

Re: Hanns-G hg281d bright band

On the signal (logic) card U7 and U8 are respectively the 3.3V and 1.8V LDO regulators. Measure the output voltage of each; use the ground ring around the mounting hole just to the left of U8.

and

U7 has 3.28v in, 1.53 out, U8 has 1.77v in, 1.49 out

doesn't add up? Am I missing something?

[rbet]

Re: Hanns-G hg281d bright band

Looks like no solution on this thread? I have the same monitor with same symptom, except this one was only intermittant for a day or two, then permanent light band. What the original post didn't describe is that images are delayed in the light area, sometimes to the point they seem frozen.
Bad Panel?