Hanns-G HG281D 28" TFT - Multiple Problems

[Rtech]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Certainly a very bad thing,and apart from the Bridge and fuse,it probably feeds a Mosfet on a heatsink,and you will need to check that as well.If you have not done that before,then this may of help.
http://www.4qdtec.com/mostest.html

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Ok, Recifier looks dead for sure. It's a general purpose bridge rectifier, 10Amp 600V type. Data sheet attached. Replace both fuse and bridge rectifier with similiar ratings.

The best way to test transformers is to do a resistance check as you are doing and perform a check with a 'ring tester' and if you search here there are many discussions on that topic. I have the 'Blue Ring Tester'.

See https://www.badcaps.net/forum/showth...highlight=ring

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Thank you much.

Ordered the bridge rectifier from Mouser.

As for the ring tester, I can't find any for sale, couldn't afford to buy one if I could, and don't have the patience or the funds to buy all the parts, etch the board and build one. So I think I'll pretty much have to cross my fingers and hope those low/no resistance readings on the windings are normal. If they're not, there doesn't seem to be any way to order a replacement at this point, which means I'd have to somehow procure a non-working Viewsonic or Hanns-G for cheap and use it for parts.

I have a feeling that if the bridge rectifier shorted when the heat sink touched the chassis and blew the fuse, there's probably a good chance the transformer was saved. That being said, I have absolutely no idea what I'm talking about so here's to hoping!

@ Rtech - Thanks for the pointer on the Mosfet. I'll definitely make sure I learn how to properly check all of the components this time, rather than just checking for shorts/diodes/etc.

SK

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Steve,
It's ok if you are on a budget! That's the whole point, and you will learn more by solving the issue rather than throwing parts or test equipment at the problem.

Forget about the traffos for the moment. Focus on the Mosfet, I would check that right away. Post the markings on it so I can check the data sheets, as sometimes there are diodes and or resistors built into the device that casue confusion. Then check for shorts, firstly in circuit, and if low readings are obtained, remove the device from the circuit.

Reason to do it now: Save on shipping costs with one order from Mouser!

FYI: AnaTek Ring tester can be found at http://www.anatekcorp.com/bluert.htm price is $42. If you were doing alot of electronics repairs, I'd recommend one!

Can you identify the MOSFET?

[retiredcaps]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

It's a 4 pin D10XB60. 1+ 2~ 3~ 4- Pins 3 & 4 are shorted, either way you look at them.

Dumb question: This is a bad thing, isn't it?

If you look at a picture of the bridge rectifier like here

http://upload.wikimedia.org/wikipedi..._rectifier.jpg

you will see it is made of up 4 diodes. When the pins are shorted, the fuse will likely blow.

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Phihong Technology Company in Taiwan manufacture this power supply and it's found in several other Monitors/TV's also. The link below shows a very similar PCB to your board.

http://www.phihong.com.tw/tw/ViewProduct.php?p_id=165

If you do get it running, expect a 5V standby voltage, and once the monitor powers on 5Volt, 12Volt and 24Volt outputs.

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Focus on the Mosfet, I would check that right away. Post the markings on it so I can check the data sheets, as sometimes there are diodes and or resistors built into the device that casue confusion. Then check for shorts, firstly in circuit, and if low readings are obtained, remove the device from the circuit.

I have done a very quick check of the Mosfet in circuit and it acts like a transistor on the meter somewhat - no low readings, only in certain directions, etc. Haven't taken it out and followed the guide yet.

Part # 2SK3568
Here is the datasheet on it: http://www.vishay.com/mosfets/list/product-91207/

There are 2 identical FETs next to it.

Part # RFP22N50A
FETs datasheet: http://pdf1.alldatasheet.com/datashe...SK3568_09.html

There is also a 2-pin TO-220 type diode on the opposite side of the Mosfet bolted to the heat sink. The diode tests ok.

As for that link to the Phihong Power board - Hells yeah!! Thanx!

@retiredcaps: This is a GOOD thing!

SK

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Ok,

From the data sheets you will see that both types of MOSFET have a diode connect in reverse across Drain - Source.

If you are getting low resistance in a particular direction, can you clarify what pins you are checking, what colour leads are connected and what values you measure? What range are you using on your DMM etc?

In fact all 3 MOSFETS should give pretty similiar results on your meter. The problem is what 'What's is similar or typical?' So report what you measure, there is enough experience in this fourm to guide your next steps.

You may not need to pull them out just yet!!! It can be alot of extra work!

Just to note: If you do decide to remove the MOSFETS individually, there may be some insulating material between the device and the heatsink. It's not always needed, but if it's there, it electrically isolates the drain of the MOSFET from the Heatsink which is grounded, be carefull not to damage this material, better still replace it with a new one when refitting. There will be a white/grey residue stuff which is heatsink compound, and it improves the thermal contact between the device and the heatsink. This helps dissipate heat from the surface of the device more efficiently. You will need some of this also.

I would recommend you desolder all 4 components and pull the heatsink out with all components still attached if that makes sense. Don't disturb them on the heatsink if you can avoid it! Then Check them all again!

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Ok. I will check them in circuit and report my readings, scale, etc.

As for the heatsink, unfortunately this particular heat sink rail is soldered onto the board with very large pegs, and my iron is not near strong enough to tackle them (especially with it being an actual "heatsink" and all ;-). So I'll have to work within the bounds of what I have ATM and hope these in-circuit readings are acceptable. If they're questionable, I guess I'll need to go out and get a bigger iron right away.

Here we go: ("~" = infinity) ("*" = Reads for 1 second on 2K scale, counting up and going to ~)

Q101 - IRFP22N50A
Pin Combo | Reading | Scale
-1 +2 _______ ~ _____ ALL
-1 +3 ______ .744 ____ 2K
+1 -2 _______ * ______ 2K
+1 -3 ______ 1.100 ___ 2K
-2 +3 ______ .507 ____ 2K
+2 -3 _______ ~ _____ ALL

Q102 - K3568
Pin Combo | Reading | Scale
-1 +2 _______ ~ _____ ALL
-1 +3 ______ .767 ____ 2K
+1 -2 _______ * ______ 2K
+1 -3 _______ * ______ 2K
-2 +3 ______ .554 ____ 2K
+2 -3 _______ ~ _____ ALL

Q103 - K3568
Pin Combo | Reading | Scale
-1 +2 _______ ~ _____ ALL
-1 +3 ______ .733 ____ 2K
+1 -2 _______ * ______ 2K
+1 -3 _______ * ______ 2K (Or reads ~ immediately, apparently depending on state of Q102)
-2 +3 ______ .542 ____ 2K
+2 -3 _______ ~ _____ ALL


By "depending on the state of Q102" I mean that the DMM introduces a voltage into the device on the 2K and lower scales and apparently changes it's state.

SK

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

I pulled out a resistor from right next to the bridge rectifier, as it was measuring .04 ohms and the meter zeros out at .03 ohms. It was covered in black shrink tubing. Upon removal of said tubing, no visible damage.

Color codes are: Brown Black Gray Gold Red.

If it's a resistor, it should mean 1 0 8 .1 2% - which is 10.8 ohms at 2%. Not really sure if the first band is brown or red, but if it is red that puts it up to 20.8... which makes a reading of .4 even more of a problem.

The gray band looks VERY silver to me, but there is no possibility for that in color coding of either resistors or caps, so I am going with gray.

Also, in person the red/brown seems to be reversed. In other words, what appears red in the images appears brown in person and vice versa. But I have a real hard time believing this is a 1%er, and my eyes are bad, so I just don't know.

(My phone camera sux, so I used a lense component as a makeshift macro lense, thus the weird circle.)

Any help would be much appreciated! Thanks

Steve

[Badcappy]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

That is likely an inductor.

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Appreciate the problem removing the Heatsink. You would need a stronger iron to do it.

Looking at the MOSFET readings, I would say leave them where they are for the moment. All readings are at least a couple of hundred ohms.

I would expect something like a 001 ohm reading on the 200ohm lowest scale if there was a dead short. You could still have open circuit or other failure modes. Some might suggest removing and doing various tests at this point.

For the looks like 'Resistor component'
Are there markings on the board where this component came from? Is it designated R, L or C in the same way that the MOSFETS have Q meaning transistor printed on the PCB??
Look for clues.

If you can post some better pictures of front and back of PCB with all shields removed. Indicate where it was taken from?

And I make the colours Brown, Black, Grey, Gold and GREEN! Making it a resistor of 10.8 Ohm +/-0.5% if the board confirms an R designation. Is that just me?

Right, I'm off!
Happy New year!!

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

For the looks like 'Resistor component'
Are there markings on the board where this component came from? Is it designated R, L or C in the same way that the MOSFETS have Q meaning transistor printed on the PCB??
Look for clues.

If you can post some better pictures of front and back of PCB with all shields removed. Indicate where it was taken from?

And I make the colours Brown, Black, Grey, Gold and GREEN! Making it a resistor of 10.8 Ohm +/-0.5% if the board confirms an R designation. Is that just me?

Aaah yes... the PCB item number markings. DOH!

It's a resistor. R106.

I have checked it against "standard" green used in resistor marking and it seems way too dark to me. That being said, I am only color blind between certain shades of red, brown and green. lol

BTW, earlier I meant to say that it is located next to the filter capacitor, not the bridge rectifier.

[pedro]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

I pulled out a resistor from right next to the bridge rectifier, as it was measuring .04 ohms and the meter zeros out at .03 ohms. It was covered in black shrink tubing. Upon removal of said tubing, no visible damage.

Color codes are: Brown Black Gray Gold Red.

If it's a resistor, it should mean 1 0 8 .1 2% - which is 10.8 ohms at 2%. Not really sure if the first band is brown or red, but if it is red that puts it up to 20.8... which makes a reading of .4 even more of a problem.

The gray band looks VERY silver to me, but there is no possibility for that in color coding of either resistors or caps, so I am going with gray.

Third band silver =10^-2 multiplier - so a 0.1 ohm resistor.

As posted in another thread, see attached ex http://en.wikipedia.org/wiki/Resistor_color_codes

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

OOOOH! The Samsung comment. ouch! My friend just bought a Samsung monitor. lol

Thanks Pedro. Got it.

So Mikeley - and anyone else willing to help me on this project - I've put the resistor back and now I'm just waiting on my bridge rectifier to arrive. I've also checked all SMDs again, just to be sure I didn't miss anything, and desoldered and checked the optocouplers. No problems there. Is there anything else you suggest I do before installing the rectifier and letting her rip one more time?

I decided against changing out the caps until after I get the fuse blowing issue resolved, just to be sure I'm not introducing any new problems into the equasion before I troubleshoot that. Is this a good idea or not?

Thanks,
Steve

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Will have fingers crossed tha the rectifier is the problem here.

Check for short capacitors/MOV's circled and perhaps ensure the varistor is ok, ie high resistance at room temperature and if you heat gently with a hairdrier, resistance should fall rapidly. This component protects the circuit from high inrush currents when the circuit is energised from the mains.

Also check your filter Cap. Any signs of leakage? They rarely fail, but sometimes do. Measure resistance and capacitance, aside from that without an ESR meter or scope, substitution is the only option.

You almost certainly will need new capacitors else where, and if you have them, intstall before powering up again.

In a workshop situation, I would take precautions to further limit the current into the powersupply after a repair by using a lightbulb in series with the mains. I have a purpose built jig that I can plug into. In your case, be ready to remove power quickly! Take precaustions working on the mains. The fuse will pop again if a short exists. Do not be tempted to short this fuse out.

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Checked Caps & MOVs. Don't have a capacitance meter, but cap works - I charged it with a 9v and lit up an LED with it several times/checked voltage/etc. Looks excellent too.

Will have to order caps - none on hand. Fortunately, I ordered 4 fuses and a PCB mount holder for them, so I have 3 left and can plug/unplug them easily. (Glad I thought ahead on that one! ;-)

Will report back when I get her all put back together. Thanks!

SK

[stevekasian]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

I received my bridge rectifier the other day and all my power board caps today. I put it all back together and wallah! I'm looking at a 28" 1920x1200 display as I type this :-).

So I fixed the power board problem. And in the process, I've eliminated the power board as the cause of my screen blanking issues, as it is still doing the same thing it was before. It just turns on now, and doesn't seem to run nearly as hot.

My next step is to order the caps for the main logic board and hope that replacing those remedies my issues. After having learned a whole lot more about how these monitors work and then reexamining the symptoms, it would seem logical that it's the logic board (no pun) causing the remaining issues.

I will radio back once I swap those babies out and let you know how I did!
Steve

[Mikeley]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Now that is good news and result! I would not rule out the capacitors on power supply yet.

In the absence of an ESR meter, the most reliable way to solve your problem is to replace the electrolytic caps on the PSU board. These caps are stressed most by high ripple currents, and harmonics in filtering the rectified output from the power supply. Typically these caps are the issue. Post the make, values and any other numbers on the PSU Caps. Measure height and diameter and order accordingly.
See post #3

By all means eliminate caps on the video/logic PCB also. These tend to to be stressed less, but depending on the make/series may just be poor quality and at or near end of life. I count 19 there.

[inkragonor]

Re: Hanns-G HG281D 28" TFT - Multiple Problems

Hello all... I am brand new to this forum, and a novice with electronic repair. But I have the EXACT same monitor as stevekasian, the Hanns G HG281D 28" monitor, min was manufactured Sept 2007. Mine also has the EXACT same problem. Over time, it's gotten less likely to turn on from completely off mode (no light). Once it's on... beautiful! Works fine, can go from On to Standby without problems.
The last time we got it started, we left it on for at least three or four weeks. Then, it got turned off by a power outage and we cannot get it to turn on at all. I searched around the internet, and thank God I found this forum.

I'd like to repair this monitor. I can send photos once I take it apart... but I'll need some help with what to do once inside. Stevekasian, if you can offer me any advice as I get into this, please let me know. I'll get some hi-def pictures to post.

It seems that the Hanns G had it's problems, but apparently they can be fixed.

Thanks in advance!