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revjames

Massive TV with black screen

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revjames

Currently trying to repair a Cello C85ANSMT-4K LED TV. Its just over 2 years old and cost over £2K new. Customer says it just went blank when he switched it on one morning. Still playing sound but no picture at all. TV powers up but no backlighting coming on hence lack of picture. Backlighting is made up of 4 circuits of 2 strips running horizontally. PSU board also feeds backlighting, tuner and picture boards which are all getting respective voltages, 5V, 12V etc from PSU. I'm told customer has had settings for brightness and contrast at 100% so LEDs been running flat out. Tried to measure voltage going out to the backlights and it starts at over 100v quickly dropping to 0. 

 

I think the LED backlights are cooked but how do you test them? not sure what voltage to apply to them and little info available online.

 

So its either the LEDS or the PSU board but need to know a bit more. Any TV experts out there? 

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ProDave

Probably the LED's.  Best of luck fixing that.  Why they are not made to be easy to replace beats me.  I have done a couple and usually you have to very carefully dismantle the actual LED panel which is a very delicate operation and risk of damaging the screen very high.  The larger the screen, the more delicate job it is. My success rate has been about 50% I would only attempt it on the basis the customer accepts the risk and if the screen breaks that is just too bad.

 

BUT before you try a repair, if it's only 2 years old they should try a claim on the supplier under the sale of goods act I think that generally expects something to work for 3 years.

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revjames
3 hours ago, ProDave said:

Probably the LED's.  Best of luck fixing that.  Why they are not made to be easy to replace beats me.  I have done a couple and usually you have to very carefully dismantle the actual LED panel which is a very delicate operation and risk of damaging the screen very high.  The larger the screen, the more delicate job it is. My success rate has been about 50% I would only attempt it on the basis the customer accepts the risk and if the screen breaks that is just too bad.

 

BUT before you try a repair, if it's only 2 years old they should try a claim on the supplier under the sale of goods act I think that generally expects something to work for 3 years.

 

The 'customer' doesn't want it back. if I can fix it its mine :) if it were mine I would have been on the phone to Cello, but I don't know all the circumstances, if all else fails it will go in the WEE skip.

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ProDave

If you can't fix it, strip out the pcb's (often only one on a modern set) and put it on ebay.

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Geoff1946

Once upon a time I understood TV sets and could fix them. I won't say how long ago that was but they were full of fire-bottles and doubled up as space heaters!

Does anyone know of any publications available which describe how the modern sets work and goes into the practicalities of diagnosing and repairing backlights and so on?

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ProDave

You could try this forum https://quuq.org/forum/index.php

 

But what you will find is most tv "repair" now is board swapping.

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revjames

Well pretty sure its backlights. I have ordered a tester for a few quid which will power up the LED strips if they still work and will tell me if they don't. If they don't its likely its scrap as I can't find replacements. If the strips are OK then I know its the main board with the PSU etc and thats £53. worth a go as theres no labour charge and if I get it going it could be worth a grand.

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Geoff1946
3 hours ago, ProDave said:

You could try this forum https://quuq.org/forum/index.php

Thank you. That looks interesting.

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revjames

just tried to register unsuccessfully.... can't search for anything unless you are a member

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Geoff1946

I failed to register too. It just says "an error occurred".  Thought it was just me.

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revjames

Just an update on this, bought an LED tester for £12 and revealed that the LED strips are divided into 4 circuits, 1 is non functioning. Good news is it looks like the rear of the TV will come off rather than the usual way of removing the LCD panel to get to the LEDs. Still not sure where I can get replacements from...

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ProDave

Good news on the LED strips possibly being accessible.

 

Ebay is a good source of tv parts,  have a look at these https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=Cello+LED+strip+&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=Cello+LED+strip+C85

 

I don't see your set listed there.  If you can get to the LED strips and get the faulty one out, look for any part numbers on the actual LED strip and search for that.

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revjames

its now scrap. I was trying to lift it up onto a frame I built to work on it, I inadvertently managed to scratch the screen in 2 places and cant be polished out as theres some kind of coating on it. Gutted

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ProDave

Don't give up.  Treat it as a training exercise or practice run.  If you can get it working you might find the scratches are barely noticable?

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revjames
50 minutes ago, ProDave said:

Don't give up.  Treat it as a training exercise or practice run.  If you can get it working you might find the scratches are barely noticable?

No its no good, tried to polish scratches out but thats taken off some kind of coating so its toast. However, I have learned a huge amount about these kind of TVs and know how to test for backlighting etc and prove the backlighting with tester before ordering replacement boards etc. Don't know if its cost effective where you have to remove the bezel and the LCD panel and diffusers to get to the LED strips. I won't go looking for TVs to fix but at least when they do come along I'll be more keen to have a go. I have had a considerable amount where the problem is simply a 20p diode.

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Sharpend

So what’s the purpose of this coating? Surely it is not a necessity for its operation? If so I can see a lot of insurance claims when the kids scratch the screen? 

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revjames
Just now, Sharpend said:

So what’s the purpose of this coating? Surely it is not a necessity for its operation? If so I can see a lot of insurance claims when the kids scratch the screen? 

Probably anti reflection. I have a 10 year old plasma with a glass screen and thats terrible for reflections

 

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