Another HannsG HG281D

[budm]

Re: Another HannsG HG281D

Do not worrying about 44mV potential diff (you will always have resistance between point A and Point B for Voltage to be developed, beside, 44mV is way too low to affect logic level), concentrate on as to why you are not getting 12VDC to the T-CON by checking Voltage on that Q14 pins base on data sheet so you can see which pin is the feeding pin., it is more likely to be P-Channel MOSFET, so the 12V should be fed to the Source pin may be via some kind of inductor.

[Capt. Cap]

Re: Another HannsG HG281D

Sorry for the delay in response. My laptop from which I usually visit BCN decided to get corrupted HDD / Windows boot sector.

No worries, I hope you didn't lose anything Sounds like my typical week.

Anyways.
Yes, if T-con is not getting power, then we need to look back on the logic board. T-con usually runs on either 3.3V or 5V. Follow the power pins on the t-con board going back to the logic board. Using this picture as a reference...
https://www.badcaps.net/forum/attach...2&d=1538959176
... you can see that there are 4 pins on the right side of the LVDs connector. After the first one, the next three have a trace that goes to fuse F400. Color-wise, those wires appear to be the just orange and red with the 3rd pin being unused. So follow these two orange and red wires to the logic-board.

On the logic board, there is likely going to be a PNP transistor or MOSFET that switches power to the T-con board. Using this picture uploaded by user Mishannya...
https://www.badcaps.net/forum/attach...3&d=1285531627
... and assuming your logic board is exactly the same (pictures of yours still wouldn't be a bad idea, just so we can verify), it appears that Q14 (8-pin SOIC chip) may be what switches power to the t-con. Because I can't see if that is 100% true, use your multimeter's continuity/lowest resistance setting to find what switching component these two orange and red wires on the LVDS connector connect to. If it's a PNP transistor, it may have gone open-circuit. If it's a MOSFET, it may have a Gate shorted to ground, which won't allow it to turn on.

I'll check resistances on Q14 tonight, see my reply to budm for voltages.
I have v6.0 of the board, it's mostly the same but seems to have less parts populated, pictures are pending.

The issue could also be that this switching part is not getting a signal from the main controller to turn on. In that case, we will have to investigate what exactly controls this t-con power switch and why it is not getting a turn on signal (for example, it could be that the bad caps on the t-con caused too much noise and corrupted the flash chip, which then doesn't allow the main controller to boot and run everything else... though that's unlikely.)

The CCFL switches on and off at the appropriate times when the computer starts / stops sending video to the display, so something is getting signalling from somewhere, though I don't know how much logic board is involved in kicking the CCFL on and off.

All of my cheap red Harbor Freight multimeters are like this. I still use them a lot, though.

If that's not the issue, you may need new probes then.

Lol, how did you know?
Yep, it's a cheap (free) red Harbor Freight multimeter, in this case the problem turned out to be a loose wire in the ground probe - jiggling it causes the resistance to jump around.

I just used another I had in a drawer for recent measurements, probe-to-probe resistance on that one was 0.8 Ω, F400 looks totally fine when using it 👍

Can't have too many multimeters.

[Capt. Cap]

Re: Another HannsG HG281D

Logic board PM549DA3 M06 VER6.0 images attached

Q14 is a 9435GM P-channel enhancement-mode power MOSFET
Q15 is a 2N70002K N-channel enhancement mode MOSFET
Pins 1-3 are source, 4 is gate, 5-8 are drain

I poked around some more with the multimeter while I had the logic board completely detached for the photo session.

For Q14,
LVDS pins marked 1-3 on the logic board (and go to F400 on the TCON) go to this drain
drain to source is 558mV in diode mode
No pins are shorted to ground, though gate sometimes looks like a capacitor charging (resistance quickly rises to infinity over a second or two)

Q15
gate is grounded, source to drain is 577mV in diode mode on the multimeter

10.1kΩ between Q14 drain and source pins (1-3) of Q15
There's > 2MΩ resistance between the +12V supply line and all pins of Q14 and Q15

FB7 & FB8
No resistance across each of them
I get infinite resistance from each FB to source on Q14
FB7 and FB8 both have 509Ω resistance to both source on Q15 and ground

Q8 (obscured by C69 in the photo) is unpopulated


Is gate being grounded on Q15 normal?
Maybe the inductors feed Q15 which in turn feeds Q14?

[momaka]

Re: Another HannsG HG281D

FB7 & FB8
No resistance across each of them

That's a problem. I have never seen small ferrite beads like that read open-circuit. Some had resistance as high as 4-Ohms due to high inductance. But never open.

Before concluding they are bad, try moving and poking harder at them with your multimeter probes. Sometimes SMD components have a layer of flux on top of them after being soldered at the factory. This can make readings appear open-circuit or high resistance until you poke and dig a little harder with your multimeter probes through the flux layer. Once you get through it, you should get an accurate reading. If they are still open circuit, they are definitely bad.

Is gate being grounded on Q15 normal?

If it was like that, then yes. Grounding the Gate of a MOSFET essentially turns it into a diode (due to the body-diode junction in MOSFETs).

Maybe the inductors feed Q15 which in turn feeds Q14?

Could be. Though I don't see why the power going to the T-con would go through two switching devices. (Read: more losses) But there could still be a valid reason for that.

see my reply to budm for voltages.

They look normal.
And I agree with budm about the 44 mV drop on ground cables - it's nothing to worry about. Even up to 1V should still technically not cause any problems. Reason why is because it's DC offset/loss. Now if this was AC noise/ripple... yeah 40-50 mV is the threshold about where things can start to act up on lower voltage rails.

Lol, how did you know?
Yep, it's a cheap (free) red Harbor Freight multimeter, in this case the problem turned out to be a loose wire in the ground probe - jiggling it causes the resistance to jump around.

I started with a really cheap meter (not HFT, though) when I got into electronics some 15+ years ago. Went through a lot of headaches during troubleshooting until I realized that 1) my probes were messing everything up and 2) meter dial contacts also caused issues to some extent (though it's a lot worse on HFT meters.) So when I started getting coupons in the mail for Harbor Freight stuff and got those meters for free (like you ), I immediately knew what to expect. One of the first things I did when I got that multimeter is stuff the probes with hot glue around where the wires exit out of the plastic handles. Believe it or not, that made the probes survive over 3 years with medium use and no problems. This only left me with the dial contacts being bad once in a while (due to high humidity here, they oxidize). Spinning the dial cleans them for a while and everything is well for a little bit. Opening the meter and cleaning everything with IPA sometimes helps for a bit longer... but I don't bother anymore.

FWIW, those HFT multimeters are not too bad for low-voltage, low-power circuits. I wouldn't trust them for high power stuff, though. There are also a few thread here on these HFT meters (and one by me, where I explain in more detail how to glue the probes and why.)

Can't have too many multimeters.

Completely agree. I got some coupons ready for those HFT meters again, next time I go in the area near the store for whatever reason.

[budm]

Re: Another HannsG HG281D

FB7 & FB8, the inrush current through those two inductors is probably 5A or more when T-CON first getting the power, they use two of them in parallel but they may be marginally rated at best.

[Capt. Cap]

Re: Another HannsG HG281D

That's a problem. I have never seen small ferrite beads like that read open-circuit. Some had resistance as high as 4-Ohms due to high inductance. But never open.

Sorry, I should have stated that clearer, by no resistance I meant 0Ω, not open-circuit. Or in this case, 0.8Ω with my HFT special

I bothered mentioning because, just like you said, they checked out bad at first due to a layer of crust over the solder. They're really finicky to check, the only reliable place to probe seems to be the very skinny top metal edge of the bead. I hate drilling the probe tips into the solder, makes me feel like I'm going to break these tiny SMD components, but it seems like the only way to get a reliable reading most of the time.

If it was like that, then yes. Grounding the Gate of a MOSFET essentially turns it into a diode (due to the body-diode junction in MOSFETs).

Ah thanks, I didn't see why they wouldn't just use a diode there, but it sounds like this is common practice, so not the issue.

Could be. Though I don't see why the power going to the T-con would go through two switching devices. (Read: more losses) But there could still be a valid reason for that.

I'm trying to figure out where the Q14 source pins' supply is comes from, but the traces are pretty hard to follow on this board. It seems like the nearby FB7 & FB8 only supply Q15, I'm not sure where to check next - should I power it on and just probe around looking for the same voltage as is at the source pins?

Now if this was AC noise/ripple... yeah 40-50 mV is the threshold about where things can start to act up on lower voltage rails.

I'll try my new scope probes later today, but the reading was very steady, so hopefully not noise.

I started with a really cheap meter (not HFT, though) when I got into electronics some 15+ years ago. Went through a lot of headaches during troubleshooting until I realized that 1) my probes were messing everything up and 2) meter dial contacts also caused issues to some extent (though it's a lot worse on HFT meters.) So when I started getting coupons in the mail for Harbor Freight stuff and got those meters for free (like you ), I immediately knew what to expect. One of the first things I did when I got that multimeter is stuff the probes with hot glue around where the wires exit out of the plastic handles. Believe it or not, that made the probes survive over 3 years with medium use and no problems. This only left me with the dial contacts being bad once in a while (due to high humidity here, they oxidize). Spinning the dial cleans them for a while and everything is well for a little bit. Opening the meter and cleaning everything with IPA sometimes helps for a bit longer... but I don't bother anymore.

FWIW, those HFT multimeters are not too bad for low-voltage, low-power circuits. I wouldn't trust them for high power stuff, though. There are also a few thread here on these HFT meters (and one by me, where I explain in more detail how to glue the probes and why.)

Thanks for pointer to your hot glue thread, I'll have to try that out!
I've never had oxidation issues on the dials, but I tend to fry or lose them before they get too old.
Another issue I've come across with these multimeters is that the probe plugs don't fit into the multimeter body tightly enough giving a bad connection there; I've found that pushing a knife into the plug slats to spread them out a little yields a nice tight fit.

[budm]

Re: Another HannsG HG281D

So at this point what Voltage do you have on the Source pin of Q14, 0V?
0V also on the two FB?
There should be big wide copper trace from the POWER 12V pin on the connector all the way to the Source pin of the MOSFET or to the inductor first before getting to the Source pin.

[Capt. Cap]

Re: Another HannsG HG281D

I figured out why I was having such a hard time following the +12V to the Q14 source pins:
Q14 source is connected to pin 4 of the power supply header, which is 5.05V and goes through FB14
1.5Ω from Q14 source to power pin 4.

Also I think I had a short between the logic board and a screw terminal the last time I took voltage measurements - I had placed an antistatic bag behind it for insulation but just noticed that it slips around bit. I hope that didn't do any damage. I'm now seeing 4.88V at Q14 source, 4.86V at drain and 0V at gate.

Apologies for the bad info guys, I'll work on getting the TCON numbers now...

[budm]

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.

[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.

[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

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.

[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

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?

[budm]

Re: Another HannsG HG281D

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

[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

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.

[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

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

[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...