Hanns-G HG281D, LCD Monitor no power

[momaka]

Originally Posted by Steven_C

Does anyone know who sells the main transformer for this monitor?

Hi Steven_C,
how did you determine the main transformer is bad? Transformers usually have a low-failure rate (LCD backlight inverter transformers aside).

Originally Posted by Steven_C

would it be possible to jumper a 12V and 24V regulated power supply to the location of the transformer pins?

If you know and can provide all of the outputs, then it should be possible. Don't hook up the external PSU to the transformer pin locations though - not unless the transformer is removed. Otherwise, you'll be connecting your external PSU across a short circuit (well, pretty much, since the secondaries of these transformers are only a few turns - which is also why they read low resistance on multimeters).
However, you said the middle pin is connected to a diode which you are not sure what voltage it is - in this case I wouldn't recommend hooking up an external PSU without first knowing what voltage should be present there. To me, it looks like some sort of feedback or power supply for U801. Not exactly sure though - the pics in this thread are pretty good, but just don't have the details I need. Feel free to post your own pictures.

Originally Posted by Steven_C

I don't get 5V although I do get 5VSB. Is the 5V derived from the 12V or 24V transformer output or do I have another board problem?

Going by the pics posted in this thread, the 5v rail does seem to be derived from the 12v output (via Q501 and Q502). But again, this is based on someone else's pictures. It's usually a good idea to post your own pictures, just in case there is a difference in the PSU board somewhere.

[heli2reg]

Originally Posted by Mishannya

OK. I've just found 3 dry caps (C603,606 and 707). Going to buy repair kit and replace all of them. Thanks to every body for your support.

I believe I have a dead power supply as well but simply have no idea where to start with the multimeter, since I have little to no electronics experience.

When I turn on the monitor, the power light comes on for a split second, then goes off. It will remain off then. I have taken the monitor apart and doubt that it is the inverter board. With a dead inverter board, I would expect the power light still remain on.

I shall dare to ask... but will attempt anyways: You got such great images and I am wondering if somebody could do a simple photoshop of how to use the multimeter to test certain important voltages?
Also, by simply plugging the power cord in, should I be able to test the voltages, or does it need the logic board with power button attached to turn on? - I am simply asking because some PC power supplies will need a pin shorted for the power supply to first turn on.

If somebody could help and post some sketches, I would really appreciate it as I would love to keep that 28" screen away from a landfill.

Thank you folks!!!

[retiredcaps]

Originally Posted by heli2reg

I have taken the monitor apart and doubt that it is the inverter board.

1) Post clear focused 2000x2000 resolution pictures of YOUR boards using the manage attachments button. Please do not post inline.

Using someone else's pictures is like asking a surgeon to operate on you using someone else's x-rays.

2) Also post a picture of your multimeter.

[heli2reg]

Originally Posted by retiredcaps

1) Post clear focused 2000x2000 resolution pictures of YOUR boards using the manage attachments button. Please do not post inline.

Using someone else's pictures is like asking a surgeon to operate on you using someone else's x-rays.

2) Also post a picture of your multimeter.

Yes, perfectly understand. Attached please find the images and I hope they will be good enough to get you the info you will need.

Thanks for responding - I really would love to have more electronics background. I hope we can get this puzzle solved.

[jetadm123]

Originally Posted by heli2reg

I shall dare to ask... but will attempt anyways: You got such great images and I am wondering if somebody could do a simple photoshop of how to use the multimeter to test certain important voltages?
Also, by simply plugging the power cord in, should I be able to test the voltages, or does it need the logic board with power button attached to turn on? - I am simply asking because some PC power supplies will need a pin shorted for the power supply to first turn on.

Thank you folks!!!

Not only will you be asked to take voltage readings, but probably resistance readings as well. If you're not well versed in how to use your meter, try viewing some videos on YouTube. There are some very good videos, which are far better than any Photoshop presentation. Just search for "how to use a multimeter".

[retiredcaps]

Originally Posted by heli2reg

Thanks for responding - I really would love to have more electronics background.

1) Those are excellent clear focused pictures. It will be used a bit later.

2) I started in the same shoes almost 1 year ago and have learned a lot.

3) To use your multimeter, there is a written tutorial in addition to the youtube videos at

http://www.sparkfun.com/tutorials/202

4) A starter lcd monitor book can be found (it will explain some of the terms we will be using)

http://www.badcaps.net/forum/showthread.php?t=10987

5) Before taking any voltage readings, connect a working computer with your favourite wallpaper to the LCD.

a) Do you see the wallpaper (even briefly)?
b) If you shine a flashlight onto the LCD, do you see the wallpaper?

[heli2reg]

Originally Posted by retiredcaps

1) Those are excellent clear focused pictures. It will be used a bit later.

That is the minimum I can do on my side since you are providing such excellent help.

Originally Posted by retiredcaps

2) I started in the same shoes almost 1 year ago and have learned a lot.

That sounds truly motivating ... I will get this monitor back up and running.

Originally Posted by retiredcaps

3) To use your multimeter, there is a written tutorial in addition to the youtube videos at
http://www.sparkfun.com/tutorials/202

4) A starter lcd monitor book can be found (it will explain some of the terms we will be using)
http://www.badcaps.net/forum/showthread.php?t=10987

AC/DC, power and voltage is pretty clear, but checking resistors, capacitors, that I have no clue of. Thanks' for the link, I will keep studying.

Originally Posted by retiredcaps

5) Before taking any voltage readings, connect a working computer with your favourite wallpaper to the LCD.

a) Do you see the wallpaper (even briefly)?
b) If you shine a flashlight onto the LCD, do you see the wallpaper?

After disassembling the entire screen to the last screen I thought I will post my response without putting it back together. Glad I did not do that, but truly built it back together and turned it on.
Wow... what a surprise. I hit the power button. Three flashes on the blue power light indicator on the screen within a half second. I was ready to post as this is what I have seen before. I waited a but, hit the power button, three flashes rapidly within a split second. Third try, same thing. Fourth try, everything remained dark. Fifth try ... wooooow ... there is the screen. Fully lit up and working with the big exception that the image appears extremely jittery towards the sides (horizontally), like somebody were shaking the image sideways at a high frequency rate, but only about 2mm. Everything is pretty legible and clearly visible.

OK, so now I got this new finding... any idea where to go from here?

Thank you again very much!

[heli2reg]

Originally Posted by heli2reg

[...]
Fifth try ... wooooow ... there is the screen. Fully lit up and working with the big exception that the image appears extremely jittery towards the sides (horizontally), like somebody were shaking the image sideways at a high frequency rate, but only about 2mm. Everything is pretty legible and clearly visible.[...]

Latest update: After responding here on the forum, I got back to the screen, and the picture was perfectly fine, clear, no issues. Even the computer could restart and everything came back up perfectly fine. I almost wanted to think that I love self-healing monitors, but I knew I would put it to the test when turning the monitor off and back on.
In fact, I did. I hit the power switch. Monitor off. Hit power switch, monitor remains off - no power light at all, not even a flicker as earlier. Multiple repeats, monitor remains off. If I give it a few hours and try again, I may see some flickers again and potentially get it to work for a short time.
I'm lost where to start from here.

[PlainBill]

Originally Posted by heli2reg

Latest update: After responding here on the forum, I got back to the screen, and the picture was perfectly fine, clear, no issues. Even the computer could restart and everything came back up perfectly fine. I almost wanted to think that I love self-healing monitors, but I knew I would put it to the test when turning the monitor off and back on.
In fact, I did. I hit the power switch. Monitor off. Hit power switch, monitor remains off - no power light at all, not even a flicker as earlier. Multiple repeats, monitor remains off. If I give it a few hours and try again, I may see some flickers again and potentially get it to work for a short time.
I'm lost where to start from here.

I've scanned your other posts and see no sign that you have replaced any capacitors. The symptoms you describe are consistent with bad capacitors (but could have other causes).

PlainBill

[retiredcaps]

To expand on PlainBill's comments:

1) Capacitors (C designation on the PCB board) die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

2) Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, and United Chemicon are suggested. A list of recommended caps can be found at

http://www.badcaps.net/forum/showthread.php?t=2280

If you live in the USA, you can order capacitors from digikey.com and get them in 2 days for $2.75 shipping costs. Most here will recommend Panasonic FR/FM or FC caps. PlainBill has instructions at

http://www.badcaps.net/forum/showpos...33&postcount=2

3) What might be happening is that as the lcd starts to get warm, the ESR (ohms) of the capacitors drop enough to let the SMPS start properly.

One test you could do is to use a hair dryer to briefly warm up sections of the power board where the capacitors are. If the lcd starts and stays on, then you know it is likely the capacitors.

[mockingbird]

If you list your caps, someone will be glad to advise you on which parts to replace them with. Incidentally, I will probably be doing a re-cap of this monitor very soon so I can post a list of what I'll be using as soon as I get my hands on the PSU and logic board.

Note that the logic board on these models also uses cheap electrolytics (Which is not uncommon, but a lot of cheaply capped PSUs at least have polymer SMD caps on the logic board (Which almost never need replacing). These caps are small and difficult to replace, and should not be attempted unless you are willing to risk destroying the logic board. Most likely they do not need to be replaced, but I always do.

[heli2reg]

Originally Posted by retiredcaps

To expand on PlainBill's comments:
1) Capacitors (C designation on the PCB board) die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

With the ESR tester, can capacitors remain on the PCB?

Originally Posted by retiredcaps

2) Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers.

What's a realistic price range for replacement capacitors for the power supply I posted?

Originally Posted by retiredcaps

3) What might be happening is that as the lcd starts to get warm, the ESR (ohms) of the capacitors drop enough to let the SMPS start properly.

Hmmm... not so sure, because after it was on for a lengthy time, I could not turn it back on immediately after turning it off. I had to disconnect the monitor from the A/C for a couple of hours, and when I hit the power button after that long "cooling off" period, I had to go through the same process as in my test this morning: Hit the power button, power light came on for a split second, and it went off. After approx two seconds, I would hit the power button again, power light comes on for a brief split second and goes off. I repeat that about 5-7 times with the cold monitor, and then eventually it stays on.

How do I get the full part list of all capacitors that I need? Take them all off the board? - I should practice some soldering skills with a dead graphics card or similar first I assume before working on a SMPS PCB that I want to resurrect.

[retiredcaps]

Originally Posted by heli2reg

With the ESR tester, can capacitors remain on the PCB?

For best results and to avoid false readings, it is best to test the capacitors removed from the circuit.

What's a realistic price range for replacement capacitors for the power supply I posted?

If you are in the USA, probably around $10 to $15 shipped.

How do I get the full part list of all capacitors that I need?

Just read the capacitor sleeve. It has all the info on it. For example, it might say Samxon GF 1000uF 10V. Measure the diameter and height of each as well.

Replacing the caps may not solve the problem. The symptoms could be cap related, but at this point, we are still gathering information.

[Lumberjack777]

It's possible you have at least one bad cap. Very probable even. But with your intermittent "works perfectly" problem I would also suspect a bad solder joint. Your pictures are excellent, and after inspecting the bottom side of the power board I can see quite a few suspects. Looks like lead free solder; and it has been known to crack or produce a less than perfect connection. But I'll leave you with the experts. They'll help you track it down

[retiredcaps]

Originally Posted by Lumberjack777

Looks like lead free solder; and it has been known to crack or produce a less than perfect connection.

I thought about that too. The photos are nice and clear, but it doesn't beat actually holding the board and using a 10x magnifying glass/loupe to look for bad solder joints.

Examples.

http://workmanship.nasa.gov/lib/insp...uirements.html

[heli2reg]

Originally Posted by Lumberjack777

It's possible you have at least one bad cap. Very probable even. But with your intermittent "works perfectly" problem I would also suspect a bad solder joint. Your pictures are excellent, and after inspecting the bottom side of the power board I can see quite a few suspects. Looks like lead free solder; and it has been known to crack or produce a less than perfect connection. But I'll leave you with the experts. They'll help you track it down

Would you be able to point me to some of the locations so I could possibly visually inspect the areas in question?

The screen has been on now for about 3 hours without a problem. Perfect picture and everything. I anticipate that it won't come on again after I turn it off now. I will atempt soon and take it apart again.

Since this trouble-shooting may be well over my head, I am thinking about sending it out to somebody for a reasonable repair price, if that's possible. With inexperience I am more suspect of making things worse than better as well. Plus I do not have adequate soldering equipment (only a propane pen soldering torch). I assume more precise equipment with temp settings etc. will be required for proper workmanship.

I will post off-site download links for the best images. I have 4-8MB original images that are way beyond the 2000x2000 mark (3500x2625 sections). Some of you may get a better view on details.

Many thanks everybody for hints and pointers!

Oh yes, and BTW: I am in San Luis Obispo, CA.

[heli2reg]

Originally Posted by heli2reg

The screen has been on now for about 3 hours without a problem. Perfect picture and everything. I anticipate that it won't come on again after I turn it off now. I will atempt soon and take it apart again.

Now that the screen was on for 3 hours non-stop and got nice and warm/hot, I have turned it off. Came back on right-a-way after turning it back on and I performed the turn-off-on cycle with 2-3sec wait periods about 5 times. After about 5 times, it would not come on. I had to hit the power button another 5 times or so. Then the power light would briefly flicker 3 times for a split second at each subsequent attempt turning the screen on. Finally, it remained on again.
So that's the symptom it's showing. Hence I think the inverter is out of question.

[Lumberjack777]

Originally Posted by heli2reg

Would you be able to point me to some of the locations so I could possibly visually inspect the areas in question?

Sorry for the slow response. I'm at work and only get access here every couple hours.

OK. Since it does come on and work perfectly, that's a very good sign. It's most likely one of two problems. It is possible you have at least one capacitor that is reaching a high ESR and throwing the whole curcuit out of balance. BUT..... for my money I'd suspect a bad solder joint. When I looked at your excellent picture of the backside; you could see what are known as "dry joints". They are the ones that are not shiney. They have a dull gray appearance. Some are half and half.
It sounds like you may not be comfortable soldering. But this is not hard to fix, even for a rookie. Just get your hands on a decent soldering iron that is well tinned on the tip. I use powerful reading glasses when I solder. Just touch the tip to the main solder joints and let it melt. Like the transformer pins. The caps. The transistors. Diodes. The larger soldering joints. If I see really dry solder I will wick it off and put in fresh solder. But you don't have to worry about that the first time. Just melt all the main solder points and see if that doesn't fix the problem. Make sure to pull straight up on the iron after you melted the joint. I'd avoid the smaller SMD components if you are not confident yet.
I'd give it 60/40 chance this will fix the problem. If not, you can always go back and remove really bad solder (and reflow it) or replace the caps.

L-J-7

P.S. Retiredcaps, you always have the best URL's to learn and watch from. Thanks for those

[momaka]

Hi heli2reg,
From the pictures you posted (which I too should say are absolutely excellent), notice in the last pic in post #64, IMG_3872, how the top-right corner is slightly darker than the rest of the board. This indicates excessive heat in that area. Now if you turn the board over (and look at IMG_3871), you will see that there are small electrolytic capacitors in that area. Chances are, they have been baked dry from the heat and are likely bad, so I would definitely recommend you replace all of them in that area. They look like CapXon KM or KF series as well - if they are indeed, you should definitely replace them because CapXon have a high failure rate, especially in hot places like LCD monitors.

As for the output electrolytic capacitors on the power supply, they look like United Chemicon KY series - those are generally very reliable capacitors and probably don't need to be replaced. I usually leave good caps alone, unless they have been heat-abused, but other members here may not agree. Also, price-wise it might not be that much more expensive to get replacements for them too.

I think a good start would be to post the info on all of the capacitors such as:
1) Brand (or logo if there is no brand name - you can already see this on the brown capacitors on the right side of the 3rd picture you posted - those are United Chemicon, which are identified by their shield logo).
2) Series (usually a 2,3, or 4 letter code, like KM, GL, etc...)
3) capacitance (uF rating) and voltage (V rating)
4) diameter and height in mm
Also list how many of each type you have and which board they came from.

[heli2reg]

Originally Posted by momaka

Hi heli2reg,
From the pictures you posted (which I too should say are absolutely excellent), notice in the last pic in post #64, IMG_3872, how the top-right corner is slightly darker than the rest of the board. This indicates excessive heat in that area. Now if you turn the board over (and look at IMG_3871), you will see that there are small electrolytic capacitors in that area. Chances are, they have been baked dry from the heat and are likely bad, so I would definitely recommend you replace all of them in that area. They look like CapXon KM or KF series as well - if they are indeed, you should definitely replace them because CapXon have a high failure rate, especially in hot places like LCD monitors.

As for the output electrolytic capacitors on the power supply, they look like United Chemicon KY series - those are generally very reliable capacitors and probably don't need to be replaced. I usually leave good caps alone, unless they have been heat-abused, but other members here may not agree. Also, price-wise it might not be that much more expensive to get replacements for them too.

I think a good start would be to post the info on all of the capacitors such as:
1) Brand (or logo if there is no brand name - you can already see this on the brown capacitors on the right side of the 3rd picture you posted - those are United Chemicon, which are identified by their shield logo).
2) Series (usually a 2,3, or 4 letter code, like KM, GL, etc...)
3) capacitance (uF rating) and voltage (V rating)
4) diameter and height in mm
Also list how many of each type you have and which board they came from.

Hi momaka,

I have tried my best at taking a soldering iron and reworking some of the dark gray and not so shiny soldering points. The result is that it really did not change anything.

However, I read through your post a couple times and it seems (correct me if I am wrong) that the power supply board may be OK despite the darker area that I could see on that as well. You clearly point out IMG_3871 and IMG_3872, which is the logic board, am I correct?

I now carefully inspected that board and found something that I wanted to share with you. I tried my best with the cam and took image P1010223.JPG.
Is that irregularity on the side of the capacitor something abnormal? Does it indicate any problem at all, potentially, or most definitely?

Logic board (IMG_3871):
As you correctly analyzed, they are all CapXon KM.

The one in question is 5mm high, has a diameter of 4.15mm
The reading says 16V, 10uF, P735
There are 12 of these total, 5 in the area you mentioned.

The others are 16V, 100uF, P729, 11mm high, 5.25mm dia, 5 total, 2 in the area you mentioned.

The 3rd type is 16V, 470mF, P735, 13mm high, 8.10mm dia, 3 total.