Hanns-G HG281D 28" TFT - Multiple Problems

[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.

[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

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?

[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

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

[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

[stevekasian]

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

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?

[stevekasian]

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

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

[retiredcaps]

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

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]

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

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]

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

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]

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

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]

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

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]

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

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

Thanks,
Steve

[retiredcaps]

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

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]

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

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

[stevekasian]

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

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

[retiredcaps]

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

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]

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

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.

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]

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

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?