Repair time (LG Flatron)

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Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 1:27 pm

My girlfriend's flatron just died. Wouldn't turn on this morning. Disconnected it, tried a new power plug, and it lit up. Put it back in place, no dice. Then it would no longer light up anywhere. Tried various outlets too just to be sure.

So, like any good gerbil, I opened it up. I took it apart carefully and i think I located the problem:

http://imgur.com/a/dU80x#0

Hopefully that clearly shows what happened. I'm far from an expert electronically so I come to you for advice. I don't even have a solder iron anymore, but I'm picking on up shortly, I have an Xbox wireless received to repair as well. Anywho - iit looks like just that resistor popped. It is a monitor from around 2007 or so, so it's not brand new, but why throw away a perfectly good thing if only 1 piece is bad right?

So it's totally apart and as you can see the damage bubbled onto an adjacent black.. thing? After I heat the pins on remove the resistor to replace, how do I cleanup the leftover gunk? Should I even bother trying to clean it up? Is it at all corrosive or dangerous? What am I dealing with? Thanks for your time! I'm fairly certain this busted resistor is the source of all the problems, I'm hoping it's a clean and easy fix before I shell out for a new monitor.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 1:46 pm

It's a diode, not a resistor, looking at the markings on the PCB and the cylindrical black package.

Edit: oh, there's more photos. Yeah, the diode (the black thing) probably died. Not the resistor.


Edit2: can you give a overview picture of the whole PCB? It might give a clue as to what the functionality of the diode and resistor was.
Last edited by Orwell on Sat Apr 05, 2014 2:12 pm, edited 3 times in total.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 1:49 pm

Orwell wrote:It's a diode probably, not a resistor, looking at the markings on the PCB and the cylindrical black package.


The black thing isn't the problem (I don't think) - I thought it was the resistor given the colored striping on it though. That and the label, usually C- is a capacitor, R- is resistor, etc.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 1:55 pm

OH ok I see what you're saying. Yeah I can take some more photos, I was running out the door and didn't expect a response so quick! Thanks, I'll take some more for you in a bit.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 1:57 pm

If a resistor fails when too much voltage is applied to it it will basically burn to a crisp until it stops conducting. This one doesn't look broken.

This more looks like the PCB has been taking a lot of heat from the diode next to it (or some other short circuit nearby).

FYI, the black thing is a diode doing anything except rectifying on the primary side of the power supply. The primary side of a power supply is the really dangerous side to do repairs on if you don't know what you're doing.
Last edited by Orwell on Sat Apr 05, 2014 2:14 pm, edited 2 times in total.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:01 pm

That's odd, I've never heard of a resistor leaking stuff.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:17 pm

If I had to make an educated guess now without any further information on the PCB and part number of the transformer, I'd say you fried some traces in the PCB and one or two components around it that caused **** to happen in the first place. The first part isn't fixable unless you buy a new power supply board.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:28 pm

Problem is, without knowing more about this circuit we don't know whether the leaking/melting component is the original cause of the failure, or merely collateral damage from another failed component elsewhere. Also can't really tell whether it is the diode or the resistor (or both?) that has failed here; that does not look like the sort of stuff I would expect to come out of either type of component. The puddle does look to be more centered on the resistor though.

Depending on what other components are connected to them, you may be able to figure out which one is bad using a multimeter.

Or, I suppose you could just try replacing both (assuming you can ID the type of diode), and see what happens. Worst case (if something else triggered the failure) it just fries again the same way.

Edit: Some wire-wound resistors have a plastic core. My current best guess is that you've got a failed plastic core, wire-wound resistor there. But still no idea whether the fried resistor is the ultimate cause of, or a symptom of, the overall failure.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:34 pm

After your advice and knowledge, I think that nothing leaked from either component, but like you said the traces heater the PCB enough to cause the coating to bubble. It's probably FUBARED. I wonder if I should try to purchase a new power supply board for it.. Hmm.
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:37 pm

Looks like I can get a replacement board on ebay pretty cheap.

http://www.ebay.com/itm/Power-Board-For ... 2c63a7699e

Certainly forth $17 to try, eh?
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Re: Repair time (LG Flatron)

Postposted on Sat Apr 05, 2014 2:38 pm

FWIW that does *not* look like burned circuit board to me; I'm sticking with my "melted plastic core resistor" theory. But yeah your best bet is still to replace the whole board if you can.

Try poking at the resistor with a screwdriver. If it bends or breaks, then the core is gone.
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Re: Repair time (LG Flatron)

Postposted on Mon Apr 07, 2014 12:24 pm

I did in fact order the power board replacement from ebay. First ebay purchase since probably 2000 or earlier. I didn't pay close attention to the shipper though, looks like it's coming from Taiwan or somewhere else overseas. 2 weeks :'(.

Gonna ask IT if I can borrow a loaner for my GF so I can get my dual setup back. My desk looks so naked.

I decided against a repair due to fear of blowing something up or starting a fire since I'm not that well schooled in this sort of thing. Probably safer in the long run - plus I have no idea if the board itself wasn't damaged too when it failed. /shrug

Thanks all for the help and tips!
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Re: Repair time (LG Flatron)

Postposted on Wed Apr 16, 2014 8:08 pm

update: Got the replacement board in today, installed it, and we're golden. Feels good to have 2 monitors again :D
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