HANNS G HZ281 White Screen

[thajenius]

Hey Guys, I've got a HANNS G that turns on to white screen. I have replaced the larger caps on the Power Board and power going to main board is steady 5.14v on two 5v leads and 5v SB. I power at the regulator of TCON board is 5.14v and 3.1v. All fuses I found appear to be ok. I have tried another TCON board with the same result. Where should I look next?

[thajenius]

Any thoughts?

[selldoor]

Yes - why have you posted these pictures off site and in line.
I am never going to wait for them to load.

[momaka]

Check voltages on test points VCC, VDDA, VGH, and VGL with respect to ground (monitor chassis). Tell us what results you get. You will need a multimeter for this.

You may have a shorted capacitor on the panel board (the skinny board attached to the panel after the T-con), or there may be a blown fuse, transistor, or voltage regulator on the logic board. Do the above tests on the T-con, and I think we will be able to narrow it down.

[thajenius]

Sorry Selldoor, I thought I read somewhere that they wanted images offsite. I don't see an option to edit the post now to fix.

Thanks for your response Momaka, Here are the voltages you asked for...

VCC = 3.288
VDDA = 4.80
VGH = .647
VGL = .952

[momaka]

VCC seems fine.
However, VDDA, VGH, and VGL are all too low. For most monitors, VDDA is normally around the 10-15V ballpark, VGH greater than 15V, and VGL less than -5V.

The most typical problem that causes this is a shorted ceramic multilayer capacitor somewhere. But as you can see, the board has quite a few of them. To *narrow down* where the shorted capacitor might be, it is best to measure the resistance between VDDA and ground, VGH and ground, and VGL and ground (of course, do this with the power OFF and monitor unplugged). Report back what resistance readings you get. Make sure to note down the scale of the resistance too - i.e. KOhms, MOhms, Ohms...

By the way, can you upload the same images you posted above in your next post please? That way, if anyone ever has the same problem with this monitor (or a similar one), it will make troubleshooting a lot easier. Thanks.

[thajenius]

Hi Momaka,
Here are the readings...
VDDA = .732 kOhm
VGH = 53.8 kOhm
VGL = 9.33 kOhm

[thajenius]

Here are the photos uploaded direct to forums, thanks again for your help...

Ill grab some pics of the little boards connected to the LCD panel tomorrow.

[momaka]

No problem, take your time with the pictures.

Looks like the rails themselves are fine, or at least don't appear to have any shorted capacitors directly on them. Than means it could be shorted capacitor in the path of VGH and VGL or perhaps whatever is generating VDDA.

So, check the following components for short circuit:
diodes D20C, D202, and D203 (for diodes D202 and D203, check all pin combinations and see if there is a short circuit between any)
ceramic capacitors C207, C212, C208, C209, and C210 (and any others you want in that area)
transistors Q203, Q204, Q205, Q206, Q207, and Q208 (again, test between all possible pin combinations).

When checking for short circuit, do NOT use the continuity (audible "beep") function on your multimter. Rather, use the lowest resistance scale. Touch both multimeter probes together and note the reading on the meter (should be less than 3 Ohms if you have a decent meter and probes). This is the "short circuit" resistance for your multimeter. Any time you see that reading or lower, you likely have a short circuit somewhere.

Report back what results you get for the above components.

With that said, I am calling it a night here and will get back to your replies tomorrow or whenever you post. Need to get some Zzz's .

[thajenius]

I started testing the items you listed and got thinking that I already tried a new TCON board so I didn't suspect that I had a shorted component there. I tried unplugging one of the cables going to the LCD (CN500) and the voltages are now as follows...
VCC = 3.53
VDDA = 13.44
VGH = 22.89
VGL -8.1

I also see that with one cable unplugged, half of the display appears to be working to some degree (See attached photos).

Also, VGL starts at -8.1v and slowly goes to -7.4v and then switches to +1.638v at which the entire display almost goes to white (you can see a faint image of the source video on the half that was previously working).

[momaka]

Originally Posted by thajenius

I started testing the items you listed and got thinking that I already tried a new TCON board so I didn't suspect that I had a shorted component there.

Ah yes, I forgot you mentioned that in the first post . Still, at least it shows us that VGH and VGL are not shorted in the TFT panel.

Originally Posted by thajenius

I tried unplugging one of the cables going to the LCD (CN500) and the voltages are now as follows...
VCC = 3.53
VDDA = 13.44
VGH = 22.89
VGL -8.1

I also see that with one cable unplugged, half of the display appears to be working to some degree (See attached photos).

Also, VGL starts at -8.1v and slowly goes to -7.4v and then switches to +1.638v at which the entire display almost goes to white (you can see a faint image of the source video on the half that was previously working).

Interesting, so it seems to be working at first - at least one side.

The fading out to white happens because VGL is responsible for "pulling" pixels in the TFT off (or low... hence VGL).

I don't see much electronic components attached to the panel board (the board that attaches to the TFT panel itself). If VGL and VGH were shorted, I think we would see them. Perhaps also check resistance between VGH_M and ground on the panel board.

Other than that, I can only think of two things: either dirty cable between T-con and panel boards (unlikely) or panel going bad. If you have access to an adjustable power supply, you could supply VGH and VGL with that. If there is a shorted transistor in the TFT, sometimes you can "zap" it with the adjustable power supply. Of course, the LCD may no longer look perfect after that.

[thajenius]

OK, ill take a look after work.
Thanks for your input.

[zwarder]

I have the same issue screen goes white after 1 second.
Did you have any success finding the fault?

[nickhog]

I have a HZ281 with opposite problem. My screen is black. Was working fine, selected a new web page, screen went black. Power light comes on and off with power switch, Power light turns green with either a VGA or DVI video source connected but screen stays black. No visible of bad caps, no burnt components or boards. Any thoughts or suggestions appreciated..

[momaka]

^ Sounds like an inverter/backlights issue. Start a new thread and post some pictures there.

[nickhog]

New thread started as requested... Hanns-G HZ281HPB Black Screen

[rrflorida]

Hi - I have the same monitor and problem as the original poster - white screen. I have replaced all the caps except the really large one. And the voltages on the tcon board are:

VCC: 3.23
VDDA: 13.11
VGH: 22.3
VGL: -9.71

Based on momaka's comments, these seem reasonable. Any ideas for me to try?

Thanks much.

[budm]

Its the GAMMA Voltages you need to report, they are V1 ~ V14 test pads next to connector CN500.

[rrflorida]

Thanks for the response, Budm. The voltages are:

V1: 12.94
V2: 12.43
V3: 10.00
V4: 9.29
V5: 8.89
V6: 8.13
V7: 6.75
V8: 6.55
V9: 6.55
V10: 4.33
V11: 3.70
V12: 3.06
V13: 0.67
V14: 0.21

[budm]

Please see this thread post #7: https://www.badcaps.net/forum/showth...ighlight=gamma