Another HannsG HG281D

[idsnmos]

Re: Another HannsG HG281D

Thanks to all for the info on the Hanns power supply fix.
I just did the "three caps" fix. Changed C603, C606 and C707. The monitor came back to life beautifully. I have three Hanns 281's and three Viewsonic VX2835's. I had sent out two previous power supplies to be repaired, but then decided to attempt a repair this time.

[momaka]

Re: Another HannsG HG281D

I was looking at the power supply board with a magnifying glass, forgot it was still plugged in running in standby mode, and accidentally touched the metal frame of the magnifying glass across some pads or traces on the back of the board on the low frequency side.

I heard a bzzzzzzzzzzzzt, quickly moved the magnifier away, but it no longer kicks on.

I get the orange and blue LED power standby lights, but when it tries to turn on, I just hear a quick, faint ticking noise coming from the power supply.

Shouldn't be too hard to repair, as it sounds like you just have damage on the secondary side. Since you do get standby power, then just check the main PS secondary-side - i.e. the rectifying diodes and of course feedback circuit (TL431 and associated resistors).

[Capt. Cap]

Re: Another HannsG HG281D

I was looking at the power supply board with a magnifying glass, forgot it was still plugged in running in standby mode, and accidentally touched the metal frame of the magnifying glass across some pads or traces on the back of the board on the low frequency side.

I heard a bzzzzzzzzzzzzt, quickly moved the magnifier away, but it no longer kicks on.

I get the orange and blue LED power standby lights, but when it tries to turn on, I just hear a quick, faint ticking noise coming from the power supply.

[Capt. Cap]

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.

[Capt. Cap]

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]

Re: Another HannsG HG281D

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.

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.

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.

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!

[momaka]

Re: Another HannsG HG281D

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.

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.

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.

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.

[Capt. Cap]

Re: Another HannsG HG281D

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]

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

[Capt. Cap]

Re: Another HannsG HG281D

Some more good news!

I removed FB14 and soldered in some copper wire across it, and got a consistent image on the right side of the display.

By gently pressing around on the ribbon cable at CN501 (right side of the TCON), I can nudge it into a position that yields a normal image on the right half of the display

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

VCC   3.31
VGL  -10.14
VGH  23.3
VGH_M 19.99
VDDA  13.57
VDDR  3.30
VDD+18V 1.80

F400 4.87
L200 left side 5.40 (moving around)
L200 right side 4.82

Gammas
V1 13.25
V2 12.91
V3 10.68
V4 9.80
V5 9.27
V6 8.41
V7 7.35
V8 7.13
V9 5.57
V10 4.49
V11 3.92
V12 2.96
V13 0.66
V14 0.22

Other
DEO 0
OE 0.61

SDA 3.30
SCL 3.30
TCONDRY 2.97

STV 0.01
CPV 1.07
MLG 1.84

VCOMs
VCOML_A 5.53
VCOMR_I 5.47
VCOML_O 5.56
VCOMR_A 5.55
(some of the VCOMs are hidden behind a foam pad)

U300 pin1 13.57
U301 pin1 13.57

STHF 0.01
FR0n 2.37
FR0p 0.13
FR1n 1.26
FR1p 1.24
FR2n 1.25
FR2p 1.31
FR3n 1.31
FR3p 1.18
FCLKn 1.25
FCLKp 1.25
FG0n 1.27
FG0p 0.13
FG1n 1.27
FG1p 1.24
FG2n 1.25
FG2p 1.24
FG3n 1.32
FG3p 1.18
FB0n 2.37
FB0p 0.12
FB1n 1.25
FB1p 1.24
FB2n 1.25
FB2p 1.24
FB3n 1.32
FB3p 1.18

STHB 0.01
LOAD 0.15
PCL  1.61
BR0n 2.36
BR0p 0.12
BR1n 1.26
BR1p 1.24
BR2n 1.26
BR2p 1.35
BR3n 1.30
BR3p 1.20
BCLkn 1.25
BCLKp 1.25
BG0n 2.37
BG0p 0.12
BG1n 1.26
BG1p 1.24
BG2n 1.25
BG2p 1.25
BG3n 1.30
BG3p 1.20
BB0n 2.40
BB0p 0.12
BB1n 1.26
BB1p 1.24
BB2n 1.26
BB2p 1.23
BB3n 1.30
BB3p 1.20

Let me know if there's anything else that would be of use here!

Momaka - resistances as follows were taken with board screwed into ground and ribbon cables in place, but disconnected from logic board (and power disconnected)

VDDA 1.90kΩ
VGL 141.8kΩ
VGH 20.3kΩ
VGH_M > 2MΩ

I attached a picture of the display, not a very good pic but I was trying to prop it up with one hand and snap a photo with the other while keeping everything from falling apart...

[budm]

Re: Another HannsG HG281D

OK, sorry I got your thread mixed up with another thread about boards swapping.

[Capt. Cap]

Re: Another HannsG HG281D

One thing that is not really clear to me is that you said you use all the boards from working monitor to connect it to this LCD panel, does mean you also use the T-CON board from working monitor also?
I also see 4 IC's on the tab bonding boards also.

All of these parts are original with my HG281D. The logic board / TCON / display combo is what was slapped together at the factory.
Some fine HannsSpree engineering for you there

[budm]

Re: Another HannsG HG281D

One thing that is not really clear to me is that you said you use all the boards from working monitor to connect it to this LCD panel, does mean you also use the T-CON board from working monitor also?
I also see 4 IC's on the tab bonding boards also.

[momaka]

Re: Another HannsG HG281D

TCON measurements follow

VCC  3.32V
VDDR 3.30
[b]VDDA 4.59V
VGL  0.46V
VGH  0.59V
VGH_M 0.18V[/b]
F400 4.85V
VDD+1.8V 1.80V

Those in the bald text are all problematic.
VDDA should be at least 10V, and not uncommon to have it to 12-15V.
VGL should be negative and VGH at least 3-8V higher than VDDA.

So it looks like Q202 is indeed not getting switched and you are just getting a diode voltage drop from the input at F400 to VDDA (normal when nothing is happening).

With power turned OFF and the t-con disconnected, what resistance do you get to ground from test points VDDA, VGH, VGH_M, and VGL?

Voltage was sagging back to 2V at Q14 source, I started poking around on the 5V line, and noticed that the right hand side of the display flashed when I touched FB14. This time, there was a kinda stripey, greyed out image on the right quarter of the display.

Could this be a bad ferrite bead?

Any ideas what a suitable replacement would be?
How bad of an idea is it to just jumper over the thing?

Since it is a ferrite bead, YES, you can jumper across it.

What you never want to jumper across is any inductor (i.e. any "L"s). For example, the 6R8 inductor on the t-con board that is connected to MOSFET Q202 is an essential component in the generation of the VDDA, VGL, and VGH rails. So if you jumper across that one, you may blow Q202 and possibly other parts.

Ferrite beat FB14 on the other hand... no problems to jumper it.

[budm]

Re: Another HannsG HG281D

For testing, you can bypass the Ferrite bead inductor and see what happen.

[Capt. Cap]

Re: Another HannsG HG281D

I was poking around the circuit boards again today, and when I checked the front of the screen, on the right half of the display, a sort of faded, discolored image was showing!



I took all new TCON measurements (numbers look much better), had the computer go back to sleep while doing so, and when it kicked back on, the screen was all white again.

Voltage was sagging back to 2V at Q14 source, I started poking around on the 5V line, and noticed that the right hand side of the display flashed when I touched FB14. This time, there was a kinda stripey, greyed out image on the right quarter of the display.

Could this be a bad ferrite bead?

Any ideas what a suitable replacement would be?
How bad of an idea is it to just jumper over the thing?

[Capt. Cap]

Re: Another HannsG HG281D

TCON measurements follow

VCC  3.32V
VDDR 3.30
VDDA 4.59V
VGL  0.46V
VGH  0.59V
VGH_M 0.18V
F400 4.85V
VDD+1.8V 1.80V

TCONDRY 2.97
OE 0.61
DEO 0
SDA 3.3
SDL 3.3

V1 4.49
V2 4.37
V3 3.62
V4 3.33
V5 3.14
V6 2.85
V7 2.50
V8 2.41
V9 1.89
V10 1.52
V11 1.33
V12 1.00
V13 0.22
V14 0.07

4.83V on each side of L200

Let me know if there are any other pads of interest!


Also, I started checking out Q202 which is a 4468 30V N-channel MOSFET.
gate & source are all 0V, drain is 4.83V - seems like this should be getting switched on but it isn't?

[Capt. Cap]

Re: Another HannsG HG281D

Never mind I just re-read your edited post #28, so now you do have 5V at the T-CON fuse then, correct?

Yes, 4.85V at F400

What is the LCD panel model number? HSD280MUW1-A00 REV 0?

Bingo!

If it is, then it runs on 5V instead of 12V that your main board version is designed for.

Well at least we know it's getting the right voltage input now.

[budm]

Re: Another HannsG HG281D

Never mind I just re-read your edited post #28, so now you do have 5V at the T-CON fuse then, correct?
What is the LCD panel model number? HSD280MUW1-A00 REV 0? If it is, then it runs on 5V instead of 12V that your main board version is designed for.

[Capt. Cap]

Re: Another HannsG HG281D

So the resistance between Source pin and the Power pin 4 (5.05V pin) is about 1.5 Ohms? I doubt that the T-CON for that 28" LCD panel will be running at 5V supply.

Yep, it's 1.5 Ohms and I just double checked all of the power pins, no continuity with anything else and Q14 source. BTW, this meter reads about 0.8V at continuity so 1.5 isn't that far off.