Plasma switches itself off

Tuck1 · 19 Apr 2011

Hi, have an LG50PS3000, 16 months old. 3 weeks ago picture occasionally would go slightly fuzzy & pink tint. Then tv would switch itself off & have to be switched back on.

Last week it switched itself off & would not come back on at all. Well, it would light up the screen for a split second then go off.

Called a local tv repair guy who took it away for asessment. He reported that the power supply unit had overheated 'like they do on these tv's' due to the power supply being 'not up to the job of coping with the heat'. Also may have affected a pcb next to the psu.

£200 later! the tv was returned with new psu fitted. When repair guy connected tv, the picture was again a bit pink & fuzzy, but some mumbling about 'switch power off & on again' and all seemed ok

This has since happened 3-4 times since, although hasnt switched itself off. He has advised to try to narrow the fault down by running the sky hd through a scart instead of hdmi. Doesnt ring true to me?

He has obviously fixed something, but not fully. What you reckon?

wotan · 23 Apr 2011

I reckon he still has an obligation to you, to repair it correctly, if he's taken £200 off you and fault is still there, he's not repaired it correctly.

Wotan

carlramsay · 18 Jun 2011

no tv expert but recently had this with a samsung, had something to do with the switches on side of tele. disconected circuit board to tv side buttons (unplugged board). can no longer use these buttons ...but can use remote for functions and tv stays on now... This is also a common fault if your tv reduces volume on its own...just disconnect board and see what happens

Mickymoody · 24 Jun 2011

Plasma TV's have a lifespan of generally 5 years. They are a false economy to people that buy them...

But these initial problems always crop up....

ALWAYS ON PLASMA TV's..

The Power supply isn't balanced corectly, for your local power supply, so a local adjustement is required, when this doesn't happen, the PSU, fails, then is replaced, but not setup correctly, and displays screen errors again, until, it once again, blows up. The replacement PSU cannot be setup locally, as it is setup from the factory.

gblades · 26 Jun 2011

Mickymoody said:
The Power supply isn't balanced corectly, for your local power supply, so a local adjustement is required, when this doesn't happen, the PSU, fails, then is replaced, but not setup correctly, and displays screen errors again, until, it once again, blows up. The replacement PSU cannot be setup locally, as it is setup from the factory.

Utter ******. Switch mode power supplies are very resilient to variation in input voltage and there would be nothing you could adjust in them. Many power supplies even work from 100 to 250v although higher power versions tend to come in two versions but thats mainly so the transformer used inside can be optimised to be more efficient at a particular voltage.

The power supply in the TV was very likely to be the cause of the main problem as its always the weak point in those TVs. When they fail the capacitor that fails often then causes other components in the power supply to get hotter and cause secondary failures. Sometimes this heat or the poor voltage stability from the power supply can cause other failures.

I wouldnt rule out your TV having two separate failures near the same time which are unrelated to each other.

Mickymoody · 27 Jun 2011

gblades said:
Mickymoody said:

The Power supply isn't balanced corectly, for your local power supply, so a local adjustement is required, when this doesn't happen, the PSU, fails, then is replaced, but not setup correctly, and displays screen errors again, until, it once again, blows up. The replacement PSU cannot be setup locally, as it is setup from the factory.

Click to expand...

Utter ****. Switch mode power supplies are very resilient to variation in input voltage and there would be nothing you could adjust in them. Many power supplies even work from 100 to 250v although higher power versions tend to come in two versions but thats mainly so the transformer used inside can be optimised to be more efficient at a particular voltage.

The power supply in the TV was very likely to be the cause of the main problem as its always the weak point in those TVs. When they fail the capacitor that fails often then causes other components in the power supply to get hotter and cause secondary failures. Sometimes this heat or the poor voltage stability from the power supply can cause other failures.

I wouldnt rule out your TV having two separate failures near the same time which are unrelated to each other.

You state utter ****, then agree that the PSU is faulty, and I gave a detailed explaination why.....

gblades · 27 Jun 2011

I explained in the first paragraph. It was the comment about the power supply needing adjustment I disagreed with not the fact that the power supply was faulty.

Mickymoody · 28 Jun 2011

gblades said:
I explained in the first paragraph. It was the comment about the power supply needing adjustment I disagreed with not the fact that the power supply was faulty.

I know of 10 cases off the top of my head, where adjustment has had to be made, due to screen distortion, that eventually led to total PSU failure. A modern switchmode PSU should work out of the box, and be autoranging. But due to a Plasma TV being so large, any slight error on the voltage lines are magnified, due to the current drawn.

A satellite receiver has the opposite problem, it doesn't need a switchmode PSU, so is basically running in standby all the time, that causes it to overhead, because it is efficient, but underrun, that in turn drys the caps out, and the thing fails. But this is a forum, everyone is allowed their opinion, so the OP can get a better understanding what may be wrong with his tv.

gblades · 28 Jun 2011

You said "for your local power supply" which implies the local mains feed. If you had said the power supply output voltage it would have made it clearer for everyone.

A underused switchmode power supply wont cause the capacitors to dry out. A switchmode pules current into a capacitor to keep its voltage topped up. Capacitors heat up due to ambiant temperature and internal heating due to their internal resistance. A psu powering a satellite receiver in standby mode is putting far fewer pules of current into the capacitor to maintain the voltage and therefore less internal heating.
The main cause of satellite psu failure is the same as a lot of equipment - poor quality components.

Mickymoody · 30 Jun 2011

gblades said:
You said "for your local power supply" which implies the local mains feed. If you had said the power supply output voltage it would have made it clearer for everyone.

A underused switchmode power supply wont cause the capacitors to dry out. A switchmode pules current into a capacitor to keep its voltage topped up. Capacitors heat up due to ambiant temperature and internal heating due to their internal resistance. A psu powering a satellite receiver in standby mode is putting far fewer pules of current into the capacitor to maintain the voltage and therefore less internal heating.
The main cause of satellite psu failure is the same as a lot of equipment - poor quality components.

I'm not going to carry on this game, the sets are setup on a regualted 240v 50Hz setup. And work fine at the factory, they are setup, and adjusted to this voltage.

Unfortunately in the UK, many are limited to 210V 49-52Hz, so the setup from the factory is now out of spec. Hence my origional post.

Sat receivers, as you are expanding to; the switchmode PSU is underrun, so overrun, due to inefficiency, then overheats, and then that causes cap failure.

Are you repairing these, seeing these, or going off heresay? Stick your meter in the mains, on the correct setting, and see what your mains is running at, certainly NOT 240V 50Hz. But when in the factory, that is what they were set to, as the market suggested. I seen them, I fixed them, why do you carry on with your game?

Monkeh · 30 Jun 2011

Mickymoody said:
I'm not going to carry on this game, the sets are setup on a regualted 240v 50Hz setup. And work fine at the factory, they are setup, and adjusted to this voltage.

Unfortunately in the UK, many are limited to 210V 49-52Hz, so the setup from the factory is now out of spec. Hence my origional post.

210VAC is below the minimum specified voltage, and both 49Hz and 52Hz are outside the legally defined frequency range for the grid. Such conditions are rare.

Many SMPSUs are designed to operate on a wide voltage range. In fact, most are now designed to operate from 100-250VAC, 50-60Hz.

Stick your meter in the mains, on the correct setting, and see what your mains is running at, certainly NOT 240V 50Hz

241VAC. I lack the equipment to check the frequency, but the grid is 50.050Hz at the time of this post.

Mickymoody · 30 Jun 2011

Monkeh said:
Mickymoody said:

I'm not going to carry on this game, the sets are setup on a regualted 240v 50Hz setup. And work fine at the factory, they are setup, and adjusted to this voltage.

Unfortunately in the UK, many are limited to 210V 49-52Hz, so the setup from the factory is now out of spec. Hence my origional post.

Click to expand...

210VAC is below the minimum specified voltage, and both 49Hz and 52Hz are outside the legally defined frequency range for the grid. Such conditions are rare.

Many SMPSUs are designed to operate on a wide voltage range. In fact, most are now designed to operate from 100-250VAC, 50-60Hz.

Stick your meter in the mains, on the correct setting, and see what your mains is running at, certainly NOT 240V 50Hz

Click to expand...

241VAC. I lack the equipment to check the frequency, but the grid is 50.050Hz at the time of this post.

You have no simple meter to check mains voltage? I think you will be shocked! As you cannot define the argument, then why still disagree with it? You lack the equipment to check the mains, then quote 50.050Hz? Hence you have the ability to read the frequency?

241V @ 50.050Hz is certainly out of range when the TV is setup, to 220V 50Hz, at the factory, hence the faults. Thus you just disproved your own idea. Incorrect voltages, cause issues on Plasma Tv's..

gblades · 30 Jun 2011

Mickymoody";p="2035797 said:
gblades said:

Are you repairing these, seeing these, or going off heresay?

Click to expand...

I am going from prior experience of designing and building switch mode power supplies.
You seem to be under the impression that a fluctuation in input voltage will somehow affect the output voltage.

Mains comes in and is rectified and passed into a reservoir capacitor.
A control circuit measures the output voltage and if it is too low it pulses the rectified mains through a transformer and the output of the transformer is then used to top up the charge in the output reservoir capacitor. All this happens about 100,000 times per second.

So if the mains voltage is lower all that happens is that the control circuit has to put a pulse of current into the capacitor more often. So if you have a power supply which needs to supply 400W with a 240V input but you want it to be able to work at voltages down to 200V then you need to design the power supply to cope with this. The end result is that at 240V the power supply will effectively be capable of supplying 480W.
Thats why it is common to see low power, power supplies capable of being able to be used with 110V and 240V (in addition to the fact that they are the devices that most people will want to take abroad) as it adds minimal cost designing them to be able to supply a little extra power. For large equipment however a dual voltage power supply is more expensive and less efficient.

Monkeh · 30 Jun 2011

Mickymoody said:
You have no simple meter to check mains voltage? I think you will be shocked! As you cannot define the argument, then why still disagree with it? You lack the equipment to check the mains, then quote 50.050Hz? Hence you have the ability to read the frequency?

I have no equipment to check the frequency myself. I do however have access to the grid frequency via other means. I do have equipment to check the voltage, which was 241VAC last night, and is presently 243VAC.

241V @ 50.050Hz is certainly out of range when the TV is setup, to 220V 50Hz, at the factory, hence the faults. Thus you just disproved your own idea. Incorrect voltages, cause issues on Plasma Tv's..

You said 240V, not 220V.

Once again, SMPSUs are not set up for a fixed voltage. They can operate on a wide voltage range and don't particularly care about frequency.

Mickymoody · 2 Jul 2011

Monkeh said:
Mickymoody said:

You have no simple meter to check mains voltage? I think you will be shocked! As you cannot define the argument, then why still disagree with it? You lack the equipment to check the mains, then quote 50.050Hz? Hence you have the ability to read the frequency?

Click to expand...

I have no equipment to check the frequency myself. I do however have access to the grid frequency via other means. I do have equipment to check the voltage, which was 241VAC last night, and is presently 243VAC.

241V @ 50.050Hz is certainly out of range when the TV is setup, to 220V 50Hz, at the factory, hence the faults. Thus you just disproved your own idea. Incorrect voltages, cause issues on Plasma Tv's..

Click to expand...

You said 240V, not 220V.

Once again, SMPSUs are not set up for a fixed voltage. They can operate on a wide voltage range and don't particularly care about frequency.

They can operate on a wide voltage range and don't particularly care about frequency

Upto the point that screen faults, and PSU issues occur....which then kills the TV....now naive is that comment? The TV 'works' for a short time, with screen issues, then blows up, as the PSU is not calibrated correctly. Obviously they do care about frequency variation, as they show screen defects, and PSU issues, due to the local supply....

If you are unaware of such issues, best not to post, if you don't understand the issues, and never repaired them.

The sets DO obviously care for overvoltage/over frequency mains, as they were set to a testbed of general voltage in the UK, and 241V @ over 50Hz isn't the norm. Then wonder why these these sets fail. They are mass produced in China or wherever...if your local supply is overvoltage to the rest of the UK, then, it will fail. The general supply is 220v @ 49Hz.

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Plasma switches itself off

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