Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Computer Displays
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 10-13-2018, 06:21 PM   #41
Capt. Cap
Member
 
Join Date: Oct 2017
City & State: SF, CA
My Country: US of A
I'm a: Knowledge Seeker
Posts: 35
Default Re: Another HannsG HG281D

Regarding this ribbon cable on CN501, it is very finnicky - if I don't leave it with a little pressure holding it just right, the right side of the display goes from normal to faded and discolored.

What is weird is that this ribbon cable should be effecting the left side of the image displayed, since the cable is the one on the right side of the TCON when viewed from the back. Or am I completely off here?

I sometimes got lighter grey horizontal rectangles, about a half inch high and spanning the entire left side of the monitor when messing around with this cable (the right side image was ugly while doing this), but never anything else on the left side.

This particular ribbon cable was creased at a 90 angle coming out of the display's connector on its left side, and then creased further down on the right side. Also, the tape covering it was pressing it against the metal display backing, which seems to have heated it to the point where it made some discolored bubble patterns on the plastic. I've tried reseating the cable a few times and cleaning it with rubbing alcohol, but still no improvement on the left side of the display.

Also worth mentioning, I couldn't figure out how to get the ribbon cable released from the connector - a YouTube video I watched had the release bar flip up in the opposite direction from these ones, and I wrenched pretty hard on them before I figured out which way they flipped up. So I could have damaged the connectors, but I've looked pretty closely, and I don't see any broken connections with the TCON board.

I'm thinking (or hoping) that this ribbon cable was just barely hanging in there, and then jostling it around when removing the TCON finally did it in?

I'm looking at replacing it, seems to be a 0.5mm pitch 80 pin FFP cable, but it has some lines missing from it.
I could sever the same wires with a razor blade, but would rather not risk screwing up the other lines on a new cable.

Do you guys think it would be fine to have continuity on the pins that have missing wires in this ribbon cable?

Is there a better way to test out a ribbon cable than checking the individual pin resistance across the cable and flexing it around? Sounds pretty tedious for 80 pins.

A pic of the current cable is attached
Attached Images
File Type: jpg ribbon_cable.JPG (608.3 KB, 2 views)

Last edited by Capt. Cap; 10-13-2018 at 06:27 PM..
Capt. Cap is offline   Reply With Quote
Old 10-13-2018, 06:24 PM   #42
Capt. Cap
Member
 
Join Date: Oct 2017
City & State: SF, CA
My Country: US of A
I'm a: Knowledge Seeker
Posts: 35
Default Re: Another HannsG HG281D

Quote:
Originally Posted by budm View Post
OK, sorry I got your thread mixed up with another thread about boards swapping.
Heh, I thought that might be the case, but your comment also made some sense since you pointed out the logic board is made for a 12V display and the panel is 5V.
Capt. Cap is offline   Reply With Quote
Old 10-15-2018, 07:41 PM   #43
momaka
Badcaps Veteran
 
momaka's Avatar
 
Join Date: May 2008
City & State: VA (NoVA)
My Country: U.S.A.
Line Voltage: 120 VAC, 60 Hz
I'm a: Hobbyist Tech
Posts: 8,381
Default Re: Another HannsG HG281D

Quote:
Originally Posted by Capt. Cap View Post
I took readings from almost every test pad and some other places of interest on the TCON while the right side image was good, hopefully it can help determine if the TCON is OK and the problem lies downstream.

Scroll down in the box below to see all values...
Looks okay to me now. All the main rail voltages are there and what they should be. I think the gammas are alright to (otherwise, you would have had a faded / wrong-colored image even on the working side of the monitor.) Resistance are fine too. I had you check them only because I saw the low VDDA, VGH, and VGL voltages. But since those are fine now, then VDDA, VGH, and VGL should have normal resistances (and they do).

At this point, the issues does seem to have something to do with the ribbon cable or perhaps connector holding, since you said you could get an image if you hold it right. That rules out any dead IC on the T-con and TFT panel boards, I think.

Quote:
Originally Posted by Capt. Cap View Post
I'm looking at replacing it, seems to be a 0.5mm pitch 80 pin FFP cable, but it has some lines missing from it.
I could sever the same wires with a razor blade, but would rather not risk screwing up the other lines on a new cable.
...
Do you guys think it would be fine to have continuity on the pins that have missing wires in this ribbon cable?
Most likely it should be okay. I don't think the non-missing lines on the new cables would cause an issue. But just in case, when you get your new cable, check where these now-not-missing lines connect to. Chances are they are probably left floating. I doubt we will see anything like lines connected to ground on one side and to a signal or power rail on the other. But do check. You don't have to check every single line on the cable - just the missing ones.

Yes, there's a chance the old cable may have failed where the 90 degree bends were. However, it could also be the connector not making good contact with the cable too. This, we won't know. But if you replace the cable and symptoms remain the same, then it's probably the connector itself.

Quote:
Originally Posted by Capt. Cap View Post
Is there a better way to test out a ribbon cable than checking the individual pin resistance across the cable and flexing it around? Sounds pretty tedious for 80 pins.
If you can find the cable (and maybe for a decent price too), it might be more worthwhile to just replace it than play around with measuring resistance/continuity from board to board. Now if you do replace the cable and the symptoms are the same, then you'll probably have to do that to verify if the connector is bad too or not.

Quote:
Originally Posted by budm View Post
OK, sorry I got your thread mixed up with another thread about boards swapping.
Ha, me too, budm. I think it was that other Samsung monitor thread we were replying to.

Sorry about the mixup, Capt. Cap.

Last edited by momaka; 10-15-2018 at 07:43 PM..
momaka is offline   Reply With Quote
Old 10-16-2018, 12:35 AM   #44
Capt. Cap
Member
 
Join Date: Oct 2017
City & State: SF, CA
My Country: US of A
I'm a: Knowledge Seeker
Posts: 35
Default Re: Another HannsG HG281D

Quote:
Originally Posted by momaka View Post
Looks okay to me now. All the main rail voltages are there and what they should be. I think the gammas are alright to
Thanks for taking a look!
That's relieving to hear! Earlier today, I did Tom's T-CON board diagnosis spreadsheet mentioned here, and it had gotten me worried as it showed my VDDA as a Marginal/Fail, and "VCOM given to AVDD" (whatever that is) as an outright fail. But then again, it showed my VGL as failed also even though is was dead in the middle of the -5 to -15V range, so I guess should be taken with a grain of salt.

Quote:
At this point, the issues does seem to have something to do with the ribbon cable or perhaps connector holding, since you said you could get an image if you hold it right. That rules out any dead IC on the T-con and TFT panel boards, I think.
The image is only on the right side of the screen though, and I'm messing with the ribbon that should be effecting the left (blank) side in order to get the right side looking pretty - doesn't make any sense to me

I was also thinking it could be a tab binding board issue for the left side of the screen, so I tried checking the only test pads that I could access without figuring out how to remove the bezel.
VCOML_I, TPC2, and TPB2 were all 0V. An unpopulated solder pad was 770mV, so there is at least some power getting to the bonding board.


Quote:
If you can find the cable (and maybe for a decent price too), it might be more worthwhile to just replace it than play around with measuring resistance/continuity from board to board.
My thoughts exactly
I've got a new ribbon cable on the way, we'll see what happens when it's in place.


Quote:
Ha, me too, budm. I think it was that other Samsung monitor thread we were replying to.

Sorry about the mixup, Capt. Cap.
Lol, I wouldn't be able to keep all the threads straight either!
Thanks so much momaka and budm for providing so much insight!
Attached Images
File Type: jpg TomsTCONDiagnosisSpreadsheet.jpg (210.4 KB, 1 views)
Capt. Cap is offline   Reply With Quote
Old 10-16-2018, 11:54 PM   #45
Capt. Cap
Member
 
Join Date: Oct 2017
City & State: SF, CA
My Country: US of A
I'm a: Knowledge Seeker
Posts: 35
Default Re: Another HannsG HG281D

Turns out it's not the ribbon cable

I got the idea to swap the two cables, and the right side of the display still works with the cable I thought might be bad, and the left side of the screen is still not displaying any picture with the known good cable.

I guess the tab bonding board is next to check?
Or could it still be a TCON issue?
Capt. Cap is offline   Reply With Quote
Old Yesterday, 01:06 AM   #46
Capt. Cap
Member
 
Join Date: Oct 2017
City & State: SF, CA
My Country: US of A
I'm a: Knowledge Seeker
Posts: 35
Default Re: Another HannsG HG281D

I checked BUF07704 and got similar results to what rrflorida mentions.

U301 has INCOM of 0V, OUTCOM starts at 5V and climbs to 9.77V.
U300 has INCOM 5.47V, OUTCOM 5.55V steady which looks more normal.

Could I also have a failed BUF07704?

Though looking closely at the traces, it seems like INCOM and OUTCOM of U301 could be floating if that makes any sense.

Last edited by Capt. Cap; Yesterday at 01:31 AM..
Capt. Cap is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2018
Powered by vBulletin ®
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 06:56 PM.

Did you find this forum helpful?