Detect if electronic coil is damaged?

@bob2300nx-Ec9D7j • Oct 24, 2024

Oct 24, 2024

1.0K

Hi, I honestly do not know much about electronics but my plasma tv recently died. I opened it up and didnt see anything strange. Only thing I find weird is there are three electronic coils on the power supply board, but one of them is discolored. When I power on the tv I can tell that the three coils get power (using a voltage detector), now when I turn the tv on the tv clicks and shows an error led (instead of how it would normally turn on). As soon as the error comes on the the discolored coil stops getting power, while the other two coils maintain power.

I took a picture of the three coils. One of them is discolored (slightly darker than the other two). Could you please tell me if you notice if this could mean the coil is damaged.

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skipper

@skipper-wJtaxo • Jun 11, 2009

It's just a little tricky to get more than a "maybe it's that thing" impression with a picture or a casual look.

My advice is: take it to a shop that has the equipment, or get some yourself. I would also recommend the manual specifically for the TV model you want to look at fixing, a book on Electronics will be useful but you want to do as little debugging of the circuit design as possible - it saves a lot of time for starters. You don't have to be an expert etc.

What your picture appears to show are choke coils across, maybe, the power rails to smooth the AC. If one of the rails is dead or overvoltage I would not recommend powering it up, you can still investigate the circuit when it's not live.
From experience, the top coil of the three does look discolored. Can you notice a burnt smell when you get close to it? Does it or the other coils warm up? Usually the enamel cooks or goes dark when you cook a coil. If you get an internal short the coil is DOA.
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bob2300nx

@bob2300nx-Ec9D7j • Jun 11, 2009

skipper
It's just a little tricky to get more than a "maybe it's that thing" impression with a picture or a casual look.

My advice is: take it to a shop that has the equipment, or get some yourself. I would also recommend the manual specifically for the TV model you want to look at fixing, a book on Electronics will be useful but you want to do as little debugging of the circuit design as possible - it saves a lot of time for starters. You don't have to be an expert etc.

What your picture appears to show are choke coils across, maybe, the power rails to smooth the AC. If one of the rails is dead or overvoltage I would not recommend powering it up, you can still investigate the circuit when it's not live.
From experience, the top coil of the three does look discolored. Can you notice a burnt smell when you get close to it? Does it or the other coils warm up? Usually the enamel cooks or goes dark when you cook a coil. If you get an internal short the coil is DOA.
I can not find really any info on this tv. It is made by electrograph which went out of business 3 weeks ago. Tv is about 4 years old so its not worth taking to a tv man.

I smelt it and did not smell anything unusual. I did find a broken fuse which I doubt is the only problem but I am going to start with that.
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skipper

@skipper-wJtaxo • Jun 11, 2009

An experienced engineer might mention that replacing a blown fuse is often the shortest path to another blown fuse. You have to uncover why the coil looks discolored, why the fuse blew or you'll be replacing fuses.

Have you looked at replacing the PS or not much hope of finding one?
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bob2300nx

@bob2300nx-Ec9D7j • Jun 11, 2009

skipper
An experienced engineer might mention that replacing a blown fuse is often the shortest path to another blown fuse. You have to uncover why the coil looks discolored, why the fuse blew or you'll be replacing fuses.

Have you looked at replacing the PS or not much hope of finding one?
Yes I have. Surprisingly all the boards inside that have a manufacture listed are samsung, which makes finding it much easier. This board on ebay has the same model number as the board in my tv. There are slight differences like a few extra heatsinks. But I suspect is that electrograph took the basic board from samsung and added a few extra touches.

#-Link-Snipped-#

What im doing now is I figure if im throwing the board out anyways might as well try some cheap parts. Also if I have to buy a board and then solder on it then I figure I might as work on the board I have. I am pretty sure that board is the problem though as to which part I have no idea (other than the coil), reason being is that the other boards have very few capacitors, resisters, or anything that I would think could go wrong. The other boards are mostly for fans and AV input.

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skipper

@skipper-wJtaxo • Jun 11, 2009

Ok , have you considered that the coil isn't or wasn't faulty? The problem could be because a power transistor has failed, or an op-amp somewhere. Coils, resistors and capacitors are more robust. Usually electrolytics burn out first, then coils; capacitors and resistors are entirely passive they only make heat. Other parts can 'vibrate' to a thermal limit, when this is exceeded all the smoke inside them, is released. (?)

Smoke is a very important component, that you really want to keep inside these parts. If you see smoke, it's usually already too late (to put it back)...

p.s. that last is from the anecdotal engineer's manual, btw.
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