Hanns-G HG281D 28" TFT - Multiple Problems

[stevekasian]

Hi,

I have the above mentioned monitor and am attempting to repair it.

I bought it used, as is, and had a problem with it right from the get-go.

First, whenever I would use the RGB input with any computer, the video display would have lots of wavy lines moving around on it... much like one sees when viewing certain finely detailed patterns in HD TV broadcasts using an analog TV.

Then, I noticed that after the monitor would stay on for about 5-10 minutes, the pixels on the screen would start to... how would I describe it... well, the black areas would suddenly start getting speckled with more and more white pixels in a seemingly random pattern, and it would generate a faint buzzing/hissing sound, and then would power down into standby mode (power light still on, in the standby color - red/orange/whatever - I'm partially color blind so I just know it wasn't blue!). I would have to turn the power off and wait about 10 minutes or more before it would come out of standby mode.

So I attempted to use the DVI input. This remedied the wavy lines problem, and also seemed to lengthen the time that it would stay on before going into standby. (I should mention that whenever it did go to standby with a DVI input, the pixel issue described above would still occur just before shutdown, but not so pronounced, and without so much, if any, of the hissing as was the case in RGB mode.)

Sometimes I could keep the thing on for 12 hours or more without any problem. Other times it would go off after about 20 or 30 minutes. Whenever it malfunctioned, I would have to cycle the power several times to get it to come out of standby mode. And whenever I would power it down for any reason, even if it was working properly, it would rarely come back on right away (either by using the power switch or by cycling directly at the power cord).

Interestingly, the power button would often fail to work once it was off, and I would have to push it and hold it in, push it multiple times (and any variation/combination of such) to even get the light to come on at all (in standby mode). Once it did come on and come out of standby mode, sometimes it would go right back off again after a few minutes. Other times it would work perfectly for many hours.

The problem seemed to get worse over time. After I had it for about a year, it shut down on me one day and I finally just couldn't get the thing to come out of standby mode at all.

When this happened for the last time, it was a really, really bad time for it to... and I was having a really bad day... So, like a complete imbicile, I got angry and starting bashing the thing around (banging on the back/sides of it), as sometimes this seemed to have helped in the past. But I turned into a little baby throwing a temper tantrum and finally held it over my desk on it's back and dropped it from a height of about 7 or 8 inches multiple times. Finally the power light stopped coming on at all and it was, indeed, completely dead.

FFWD 10 months to today: I decided to learn how to fix it today because I don't want to pay Hanns-G the $200+ they want to replace the faulty board(s) for me. So after researching monitor repair and the layout of this particular model, I opened it up and found that, on the top of one of the heat sinks/covers on the PSU board, there was mark with melted metal where it had obviously shorted out to something. I noted that the casing to which it is installed has a matching mark on it as well

Upon trying to figure out how in the world this could've happened with a clearance of about 1/8" between the two surfaces, with the PCB firmly mounted to the case and the case being a very rigid metal, I noticed that the PCB has a bit of a bow in it - apparently from the excessive heat build up during it's use (this monitor always ran EXTREMELY hot).

So I've I hypothesized that when I dropped it on the desk, the PCB was very pliable due to it's temperature, and the G forces caused it to make contact with the case for a fraction of a milisecond upon impact, thereby causing the short.

So now I have a monitor with multiple problems, the second of which may or may not be related to the same board that was causing the first.

Based on my description of the initial intermittent forced standby problem, does that sound more like an issue with PSU board or with the main board?

And based on the short of the heat sink/cover to the case, is there a group of parts that would most likely have been affected by said short?

I am posting pictures of both boards for your review.

Thanks! And sorry for the long description - I just wanted to be thorough.

Steve

(sorry, these are the highest resolution images I can make right now)

[stevekasian]

Update:

I've determined that F1 (T4AL/250V) is open.

A Littlefuse #3691400000 should be an exact replacement (@300V). (http://www.littelfuse.com/products/F...691400000.html)

This particular fuse is specified as being for an electronic ballast application. Is there any reason I couldn't replace it with any Slo-Blo fuse of the same rating that fits?

[retiredcaps]

Originally Posted by stevekasian

apparently from the excessive heat build up during it's use (this monitor always ran EXTREMELY hot).

You could have dried up capacitors if this monitor ran extremely hot. See

http://www.badcaps.net/forum/showthr...=HG281D&page=2

To replace all the capacitors on your power board would probably be around $10 USD. Well worth it to save a 28 inch monitor if you ask me.

If you are in the USA, follow PlainBill's instructions on how to order Panasonic FM caps. If FM is not in stock, then go for Panasonic FC.

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

[stevekasian]

Thanks for the advice.

Is it probable that another component may have been destroyed before the fuse blew?

Is it possible that any of my newly installed caps might be damaged/destroyed if there is another problem with the circuit other than bad caps and a blown fuse?

Thanks,
Steve

[seanc]

Do you have a camera you can use to take photos instead of your phone?
The ones you have provided aren't good enough to make out any useful markings.

[jetadm123]

Originally Posted by stevekasian

Thanks for the advice.

Is it probable that another component may have been destroyed before the fuse blew?

Is it possible that any of my newly installed caps might be damaged/destroyed if there is another problem with the circuit other than bad caps and a blown fuse?

Thanks,
Steve

There's always the chance that another component blew before the fuse did. As for the newly installed caps: what brand/series of caps did you use? Not all caps can be used for monitor repair. Also, please post a photo of your power board with the cover(s) over the heatsink(s) removed.

[retiredcaps]

Originally Posted by stevekasian

Is it probable that another component may have been destroyed before the fuse blew?

Is it possible that any of my newly installed caps might be damaged/destroyed if there is another problem with the circuit other than bad caps and a blown fuse?

With your multimeter, there are a number of checks you can do. Check for shorts on the bridge rectifier, transistor and mosfets.

Just to confirm, does the picture in post #1 show your new caps? I suspect no because all the felt pen marks are on top of the caps.

Moreover, you are probably asking if I order new caps and install them, will they be harmed by some other component?

[stevekasian]

Originally Posted by retiredcaps

Just to confirm, does the picture in post #1 show your new caps? I suspect no because all the felt pen marks are on top of the caps.

No... I haven't done anything but disassemble the unit and remove the open fuse from the PCB. I'm waiting to get all my parts (and a camera for better pictures to post!) before I tear it down any further.

Originally Posted by retiredcaps

Moreover, you are probably asking if I order new caps and install them, will they be harmed by some other component?

That is precisely my question. Any thoughts on that?

I apologize that I am not ready to follow any more instructions at present, as i really do appreciate everyone's eagerness to help. I just wanted to get some preliminary information at this point to aid in deciding whether I am ready to tackle this or not.

I've determined that I am, therefore I'll need to buy a multimeter and some other tools. I also have parts on order which won't get here until I am gone for the Christmas holiday, so I won't be able to do anything more until I get back next week.

As for the brands/types of caps, I'll be following retiredcaps recommendations in his previous response.

Have a Merry Christmas! And thanks again!

Steve

[retiredcaps]

Originally Posted by stevekasian

I've determined that I am, therefore I'll need to buy a multimeter and some other tools.

If you are in the USA and not in a rush, there can be some wicked deals on ebay for multimeters. I bought an used working Meterman 15XP for 99 cents.

If you search for Amprobe, Meterman, you can find some that are less than $10.

Many say Fluke is the king and I don't disagree, but even used, you will pay a premium for them. Having said that, I managed to get a working Fluke 75 (probably 20 years old) for $20 CDN locally.

Whatever you do, don't buy the 830 multimeter variation on any kind from any asian vendor. It is total crap. I know. I bought one and luckily for me, it never worked. The build quality is horrendous.

[stevekasian]

Yeah, Flukes are tha bomb 4 sure. I used to sell them in an electronics store when I was a kid. Best you can get. Worst priced too though :-(. It's true that you get what you pay for, but I am broke - that's why I'm repairing this monitor myself!

I'm gonna go with this little 4 day special at Fry's Electronics - It's a VELLEMAN DVM850BL for $8.99. I know it's a piece of crap, but at least it's got more functions than the Radio Shack models for 20 bucks and up. It'll have to do for the first few projects.

I checked eBay for the Amprobe & Meterman units but it looks like you cleaned everyone out. lol

SK

[stevekasian]

Hope everyone had a merry christmas!

In the absence of a proper camera with which to take pictures of the board, I proceeded to troubleshoot it on my own. Here's what I've come up with so far:

I checked all components on the board for shorts and open circuits, including all diodes, transistors, schotkeys, the rectifier IC, SMDs and caps. I found none. (I did not properly check the transformers though.)

I changed out the fuse, reassembled the unit and plugged in the power cord. Immediately the slo-blo fuse popped (loudly) again, the lamp connected to the same outlet dimming dramatically in the instant before the fuse blew.

I took the board out again and rechecked for any visible damage. Only the fuse seems to have blown.

So I read up on LCD monitor repair, learned a bit more and then checked the transformers out with my multimeter (digital, unfortunately).

T2 & T3 checked out ok in circuit, but T1 seems to be shorted between all pins on the secondary ("B") except pin 4. Resistance measurements between pin 4 and all other pins on B seem to be consistent at .6 ohms. Measurements between all other pins in B come up as close to 0 ohms as the meter will get (.3).

Resistence between 1 & 2 on the primary ("A") measures .4 ohms.

I have been attemting to remove the transformer from the circuit but have found my soldering iron to be inadequate for the task. Time for a new iron I guess. It is an Unger 35 watt. It's about 25 years old. It could just need a new element or I might need a hotter iron. Any suggestions in this regard would be very much appreciated!

Is it necessary to remove the transformer from the circuit to check it properly with a meter? Unfortunately I don't have a flyback tester - and I can't even find a single repair shop within 100 miles that uses them anymore. (What is wrong with all these "repair shops" nowa-days?? They don't even do component level work anymore, they just replace entire modules!)

Thanks!
Steve

[retiredcaps]

Originally Posted by stevekasian

I checked all components on the board for shorts and open circuits, including all diodes, transistors, schotkeys, the rectifier IC, SMDs and caps. I found none. (I did not properly check the transformers though.)

For the bridge rectifier, they usually have 4 pins. Did you test 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4 for shorts?

Is it necessary to remove the transformer from the circuit to check it properly with a meter?

Generally no, but yes for 100% accuracy.

[stevekasian]

Yes, I checked all of the pins in all combinations.

Thanks,
Steve

[retiredcaps]

Originally Posted by stevekasian

I have been attemting to remove the transformer from the circuit but have found my soldering iron to be inadequate for the task.

I usually add a little 60/40 solder to the joint so that everything is molten. Then I use my solder sucker to remove the solder. Seems to work fine, but sometimes multiple applications may be necessary.

[stevekasian]

I'm using solder wick and the iron isn't even heating up the joint enough to melt the solder in any reasonable amount of time. Introducing the wick into the equasion seems to be just a little too much. It sinks enough heat away that the solder won't melt. I try priming it with fresh solder and it helps, but it's pretty much unworkable.

Do you think a 35 watt ** EDIT!! 25 WATT ** pencil should be the proper size for this type of board work? If so it is probably the heating element just needs replacing. Just don't want to replace it with a higher wattage iron if it'll end up being overkill.

[retiredcaps]

Originally Posted by stevekasian

Do you think a 35 watt ** EDIT!! 25 WATT ** pencil should be the proper size for this type of board work?

I tried with wick in the first one or two lcd repair, but switched to the solder pump. I had poor results with the wick. If you can get the joint to molten status, the pump works great.

I suspect my poor results with the wick is that it is really cheap wick.

My soldering irons are 30W and 40W sort by ebay lowest price. I paid maybe $4 USD for them and they work fine. A solder pump is also around $3 off ebay.

The local electronics store wants $30CDN for a solder pump.

[stevekasian]

Ok. Thanks. I just found a 30 watt @ Fry's for $2.99. The pump I'll have to research, as the cheapest Fry's or Radio Shack sells is about $10. It's too bad, cuz I have a Stanley sucker with a bad tip on it. It's got the replacement PN printed right on it but nobody sells the tips anymore. :-(

Based on my measurements of the transformer, does it sound shorted to you? I understand the resistance should decrease the farther you get along the secondary coil taps.

If so, do you have any suggestions on how to go about replacing it?

[retiredcaps]

Originally Posted by stevekasian

Based on my measurements of the transformer, does it sound shorted to you? I understand the resistance should decrease the farther you get along the secondary coil taps.

What is the part number of the transformer?

[stevekasian]

Where there's a will there's a way. I figured out a way to use the broken tip with my solder sucker and removed the transformer. Here are the results of the test:

Primary pins 1 & 2 are measuring .04 ohms between them.

Secondary pins 1, 2 & 3 are all measuring short between them, and all the rest of the pins are completely isolated from these (no continuity at all).

Pin 4 to 5 measures .6999 ohms
Pin 4 to 6 measures .65 ohms
Pin 4 to 7 measures .60 ohms

Pins 5, 6 & 7 all seem to measure short between them.

Markings on the transformer are as follows:

26002170001 PHIHONG
E149666 FIS-B1
904040-001 0728 RA3
HI-POT

[stevekasian]

Oops, I just realized that I confused/swapped the primary & secondary sides of the transformer in my description. :-p

And I also realized i screwed up on the bridge rectifier test. I don't know how in the world that happened, but it did.

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?