Another HannsG HG281D

[Capt. Cap]

I'm working on a recap for a HannsG HG281D monitor with a Phihong PSM-217-404-H-R rev. A1 power supply.
There are quite a few threads on this monitor at badcaps, and I've read through all of them, but have a few questions related to my particular situation.

The monitor worked fine until about a year ago. I usually would power off the monitor completely when not using it (I don't trust the plug-an-play stuff to not fry the HDMI port on my laptop), and it would not turn back on without a couple of power button presses. Once powered up into standby mode (orange LED color) it would go into normal operation (blue LED color) just fine and not have any issues during use. Getting the monitor initially powered on started to become a bit of a chore, so I started leaving it in standby mode and doing the plug-and-play thing. As long as I didn't accidentally flip the switch on the surge protector, I would be fine. Then it started to turn itself off completely while sitting in standby mode after a week or so; getting it turned back on would be quite time consuming, though sometimes it would just kick itself back on (this monitor seems to revert back to its last state after power failures). Getting the power back on became harder and harder, and now I have not been able to get this thing powered on since the last time it turned off.

From my reading about the HG281D in other threads, it appears this is likely a power supply issue, in particular, a startup capacitor problem (as mentioned here https://www.badcaps.net/forum/showpo...2&postcount=34) does that sound about right to you guys?
Which exactly are the startup caps on this board?

Sounds like the C603, 606 and 707 are also problematic, so I was planning on recapping the entire board (except for C3). I'm wondering if film capacitors would work for the 100V and 50V capacitors or would the ESR be too low? I'd like to understand which places on the power supply board are important to get low ESR, where some ESR may be necessary, and where GP caps are OK.

According to this picture linked from another thread http://www.directupload.net/file/u/4...fvxoqk_jpg.htm the primary is everything to the left of the transformers in the middle, the secondary is everything to the right. This follows a white silkscreen line printed on the back of the PCB. However there is a low ESR cap (C108) on the primary and a GP cap (C707) on the secondary - are those just bad choices? Where is the PFC on this board?

I've attached pics of my particular PSU, also an annotated pic with the cap PCB number + specs to help identify all of the caps.
Also, that picture linked above is a nice reference (it's of the rev. A2 board, all capacitor values are the same).

PCB # / brand series breakdown is as follows:
C203 C114 are Jamicon TK series (general purpose) https://cdn.badcaps-static.com/pdfs/...0a384e50a9.pdf
C205 C606 are Taicon VT series (general purpose) https://cdn.badcaps-static.com/pdfs/...6f416a420a.pdf
C601 Ltec TH series https://cdn.badcaps-static.com/pdfs/...710cf29b67.pdf
C603 C707 C111 Ltec TK series (general purpose) https://cdn.badcaps-static.com/pdfs/...eff471caef.pdf
C108 Ltec LZG series (low ESR) https://cdn.badcaps-static.com/pdfs/...3154c18b5e.pdf

C3 Nippon Chemi-Con CLA https://cdn.badcaps-static.com/pdfs/...41a221bc5e.pdf
Everything else is Nippon Chemi-Con KY (low ESR)

I also plan to replace the DC filter caps on the logic board https://www.badcaps.net/forum/showth...ghlight=HG281D

[Capt. Cap]

Re: Another HannsG HG281D

Looks like I missed C406 in that first annotated photo. Can that picture be replaced?
The corrected picture is attached.

[Capt. Cap]

Re: Another HannsG HG281D

I ended up replacing just C603, 606 and 707 since I already had low ESR 22μF and polypropylene 1μF 100V capacitors on hand, and it's worked since.

However, I've recently started to get a blank white screen after the monitor has been on for an hour or more, computer puts monitors to sleep after inactivity, and then attempts to wake it back up.
Works fine again if I let it cool off for an hour or so and then turn it back on.
I may be revisiting this one soon.

[momaka]

Re: Another HannsG HG281D

Did you recap the entire video/logic board or just a few caps as suggested in the thread link above.
I personally recommend recapping as many caps on the logic board as possible. And *don't* use general purpose (GP) caps, even if the original ones were. There are a few hot linear regulators on that board, so it's probably best to go with long life entry-level low ESR electrolytics (such as Rubycon YXJ, Nichicon PW, Panasonic FC, and etc.)

[Capt. Cap]

Re: Another HannsG HG281D

Did you recap the entire video/logic board or just a few caps as suggested in the thread link above.

I actually skipped the logic board entirely as I didn't have any suitable caps on hand.
I'll definitely pull out the logic board and do some replacements the next time I have it open.

I was thinking this could be a VGL issue. Do you think it's logic board related?
I have a scope now so diagnosing might be a little easier - any suggestions?

[budm]

Re: Another HannsG HG281D

I would at least replace those two caps for the regulator circuit on that logic board.

[momaka]

Re: Another HannsG HG281D

I was thinking this could be a VGL issue. Do you think it's logic board related?

Since the white screen issue is intermittent (only happens from time to time), I doubt VGL, VGH, and AVDD/AVCC are bad.

So yes, I suspect the logic board for that first. Definitely replace at least the two regulator caps that budm suggested. I personally suggest to replace all of the "bigger" caps on the logic board as well as everything close to the linear regulators, as those areas typically get hot and will kill cheaper caps over time.

[Capt. Cap]

Re: Another HannsG HG281D

Since the white screen issue is intermittent (only happens from time to time), I doubt VGL, VGH, and AVDD/AVCC are bad.

Maybe not so intermittent after all... I haven't been able to get the screen to display an image at all today, even on first attempt

[momaka]

Re: Another HannsG HG281D

Well, as the old (likely bad) caps on the logic board age, they will eventually dry out more and more until they get to a point where your monitor no longer works at all. I think it would also be easier to change those caps first than assuming there is an issue with the T-con rails. There still might be one, but if there isn't, we will be looking for a problem that doesn't exist, and this can complicate the troubleshooting process. In other words, let's try to eliminate the simple (potential) issues first. (i.e. the caps on the logic board)

[Capt. Cap]

Re: Another HannsG HG281D

I opened up the monitor and broke out my multimeter and oscilloscope as I wanted to get an idea of the difference any modifications make.

Apologies for the _s, I couldn't get it to align correctly with spaces.
Here are the measurements I took:



line_V______%off_______Vpp__interval_f
------------------------------------------
1.8V_1.767V_(-1.83%)_|_17mV_200ms____7.5Hz
3.3V_3.27V__(-1%)____|_38mV_200ms_____16Hz

VSB5V_4.96V_(-0.80%)_|_35mV__200ms____8Hz
+5V___5.09V_(+1.80%)_|_22mV__200ms____9Hz
+12V_12.10V_(+0.83%)_|_48mV__200ms____5Hz
+24V_23.7V__(-1.25%)_|_132mV_200ms____5Hz


Vpp should represent noise on the line, the interval is for the sample rate on the DSO138, and frequency is what I was showing more or less for the noise oscillations at that sample rate. Not really sure what is normal there, but these don't look like they're ridiculously out of line. The +5V line had some weird resonance thing going on (frequency on the noise would sometimes slowly speed up and then suddenly slow down again). All of this was measured as AC at the 10mV sensitivity with the CCFL powered on. I don't think the DSO138 is sensitive enough for measuring noise in DC mode. Also, there were oscillations going on at 60/120/240Hz but that's probably normal right?

I can replace those regulator caps on the logic board tonight, was wondering if the above info changes anything though?

[momaka]

Re: Another HannsG HG281D

When you are measuring PSU noise with a scope, You need to add two small capacitors to the osciloscope's probes. I forgot what value these were supposed to be and how to place them.... but in esscence, without those two caps, your oscilloscope's probes will act like an antenna and pick up more noise than there is. Granted none of your measured noise above appears to be too terrible (132 mV on the 24V line is not that great, though). Still, the 3.3V and 1.8V rails are linearly regulated, so the noise should be a lot lower than you measured. Not sure if that's due to picked up noise (as mentioned above) or if the caps on the outputs of those regulators really bad. But with linear regs, often times you will see less than 10 mV noise.

[Capt. Cap]

Re: Another HannsG HG281D

When you are measuring PSU noise with a scope, You need to add two small capacitors to the osciloscope's probes. I forgot what value these were supposed to be and how to place them.... but in esscence, without those two caps, your oscilloscope's probes will act like an antenna and pick up more noise than there is.

Regarding the noise measurements, I checked ground from one side of the logic board to ground on the other side of the logic board and got 14mV of noise - I figured anything much greater than that would be legitimate noise. I also got some real probes with the capacitance built-in since then, but haven't really used them yet.

[Capt. Cap]

Re: Another HannsG HG281D

I went ahead with replacing all of the caps on the logic board.
Unfortunately, I'm still seeing the same issue (all white screen).

I was pretty hopeful this would work as the 100μF caps near the regulators were really bad, as were some of those 10μF caps.
It could be that I did a crappy job of replacing them - I used some new solder and just wasn't getting very good flow-out on the pads on the top side of the board, it could also be that they were oxidized from age and not taking the solder well.
But seeing as how the symptoms are exactly the same, I'm thinking it could be something else.

What should I check next??

[momaka]

Re: Another HannsG HG281D

What should I check next??

T-con board.
That's the one permanently attached to the TFT screen and usually located at the top of the monitor, under a metal shield. It's possible the badcaps may have cause damage to the t-con board.

Take some pictures of the t-con board and post them here. The are of most interest is where around the LVDS connector (from the LVDS cable that comes from the logic board) and also there should be a round inductor and a fuse on the t-con. The round inductor is where the main boosted rail and other secondary charge-pump rails get produced. The fuse should be near the LVDS connector. Start with checking the fuse.

Post pictures and results here.

[Capt. Cap]

Re: Another HannsG HG281D

Pictures of the TCON are attached.
Let me know if there are any others I can take that would be of help.
Thanks!

[Capt. Cap]

Re: Another HannsG HG281D

Also, I checked F400, was getting some resistance there (~35 ohms) but I get that just touching the tips of the probes together.
I need to dig up my good multimeter, but in the meantime I think F400 is ok.

[Capt. Cap]

Re: Another HannsG HG281D

I started checking resistances and voltages on the TCON, the voltages were all way off (VGL, VGH, and VGH_M are all 0V) and eventually got back to F400 which has 0.84V on both sides.

Not sure what the supply voltage is supposed to be to this TCON, but it seems U404 and U406 are not going to be cranking out VCC and VDD+1.8v respectively from 0.84V.

So back to the logic board, V18S is 1.784V and V33S is 3.30V, but the pin 1 of the TCON LVDS (which carries power to the TCON) was only 816mV (same as was on the TCON at the time, it fluctuates a bit).

Any ideas which components are responsible for the supply voltage to the TCON?

[momaka]

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.

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.

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.)

Also, I checked F400, was getting some resistance there (~35 ohms) but I get that just touching the tips of the probes together.

Some cheap multimeters will do that when they have bad contacts in the dial.
One way to remedy this, temporarily, is to push down on the dial and rotate it quickly several times through the resistance scales. Then check the resistance again. Should be much lower now. Also, cheap meters have bad switch positions sometimes, so getting the lowest possible resistance on the lowest resistance scale may require to play with the dial a bit by pushing left or right on it (without changing to another scale) to find where it makes better contacts. 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.

[budm]

Re: Another HannsG HG281D

BTW, when you are testing the DCV at the fuse of the T-CON board, you have the monitor connected to the running PC?
Di you have 12VDC feeding the logic board?
And yes, Q14 is the switched MOSFET so some of the pins should have 12V feeding Voltage on the pins.

[Capt. Cap]

Re: Another HannsG HG281D

BTW, when you are testing the DCV at the fuse of the T-CON board, you have the monitor connected to the running PC?

Yes, connected, sending signal over HDMI, made sure it's not asleep, and the CCFL is powered on.

The CCFL does power on / off with connecting and disconnecting HDMI, and when the computer goes to sleep, so there is some sort of signalling still working there.

Did you have 12VDC feeding the logic board?

Yes, also checked all of the power input pins, they're as follows:

1 yellow 12.03
2 orange -0.04
3 red 4.89
4 green 5.05
5 brown -0.04
6 black 3.14
(ground reference is an on-board screw hole pad)

+12V measured on the power supply board is 12.08V

I apparently have a steady 44mV potential difference between the power supply and the logic board grounds - the logic board is not screwed into the chassis right now. I thought the ground wires running between the two boards would be good enough, I should probably do something about that. Though that could also just be providing an easier path for something shorted to ground on the logic board?

And yes, Q14 is the switched MOSFET so some of the pins should have 12V feeding Voltage on the pins.

Q14 voltages are the following (where pin 1 is the top rightmost in this pic and pin 4 is the top leftmost):
pin# voltage
1-3 1.30 - 1.56V
4 0V
the bottom 4 pins were all 0.20 - 0.35V