Flat screens

[Refugee]

One of these horrors pushed in for some workshop time today.
It was the usual old story and fortunately the fault was quick to diagnose.
Off with the stand and then no screws
Out with the paint scraper and with a couple of bashes on each side it was open and the panel removed to expose the power supply.
One capacitor replaced and it was working again.
It was actually quicker to do than the ones with 20 screws holding the back on.
No more nagging about that computer screen not switching on and staying on.

[pamphonica]

It's nice to see that even these flats-creens don't just get junked. Good repair.
I have a bit of a phobia about switched mode supplies, even though I have successfully replaced quite a lot of faulty caps in such supplies in my time.
The phobia came after I spent all day replacing 8 damaged FETs buried in a UPS (Uninterruptible Power Supply). A very fiddly dis-assembly job. I switched on 6 hours later to be greeted with an almighty bang and I now had 16 FETs showing nothing more than three blackened stumpy legs each. No sign of the plastic packaging at all! Gave up....

[Refugee]

I used to repair 700W SMPSUs that fitted in printers thae were as big as large filing cabinets. The boards cost £500 each.
What the board manufacturer had done was to fit 4 FETs on opposite sides of the heat sink with two thin screws and holes so that the insulators got crushed.
They used to blow all the FETs apart and randomly blow cmos chips and diodes all over the place. I had to check everything.
Once I realized what was going on I ordered some of those FETs with insulated tabs and countersunk the holes that still had sharp edges.
The new FETs were a quarter of the price of the originals and they never came back under warranty.

[Geordie McBoyne]

Yesterday, I accepted a Sanyo branded Vestel flat  TV for repair.  I got lucky with this one, and so did the set's owner.  The fault was a bulged 2700MFD 16volt elco.
Like the flat TV which is the subject of this topic more time was expended removing the replacing the back cover screws.
The remote control handset needed fixing as well.

Geordie McBoyne.

[Nick]

This was a pretty common problem with older flat screens from about 10 years ago - this was at the tail end of the fake/bad electrolyte scandal in Japan - also affected a lot of pc motherboards. There are loads of references to this on the web.

Our own Samsung R74-series flat screen had the same issue in the PSU a few years ago - an easy fix in the end....

[Murphyv310]

The thing with flat screens is that although a lot of problems can be PSU related and often down the the Electrolytic caps, that’s not the full scenario.
To do the job properly engineers need to invest in a cradle, to support the set when dismantled, proper de-soldering stations need to be purchased to cover the many different types of chips used, these are not cheap by any means.
Blown FET's and other semiconductors pose their own problems as although you may be fitting the correct type of component, often the original has a different mask number from the replacement and the component can fail in a short time.
The next problem is the manufacturer, so many come from China and to obtain parts can be a nightmare, boards are sometimes the only way to effect a repair, often a costly way to go. then the customer refuses the estimate.
This then leads me to two things, firstly a deposit must be taken when the set comes in, If a customer drops in a set and has no cash I would never look at the set until he or she returned with the deposit. Often this weeds out the time-wasters and of course there are very few that would pay as much as £100 on a repair to an LCD.
These sets have more and more features by the week and many just see a new set as an upgrade anyway.
Its funny though so many now watch catch up on their phones and tablets, TV sales are down as is Licence numbers, the TV "trade" is gone nothing like it once was, so many though seem to think it will come back, that is just living in fools paradise!

[Nick]

All my soldering equipment is Metcal - used to have a QX2 rework station but sold that as the heads were simply too expensive to have one for every type of package, it was too big and it wasn't used nearly often enough to warrant the desk space.

Love the MX-500(0)s and the DS1s - never let me down.

[Refugee]

I have seen flat screens that loose all there firmware if the capacitors go open circuit. You have to "hack" a known good set to get the firmware back on it again.
The best bet is to get another set that has a broken panel and "rob" it for the boards and be sure to replace the same caps on the replacement before they kill the firmware again.

[Murphyv310]

I have seen flat screens that loose all there firmware if the capacitors go open circuit. You have to "hack" a known good set to get the firmware back on it again.
The best bet is to get another set that has a broken panel and "rob" it for the boards and be sure to replace the same caps on the replacement before they kill the firmware again.

Hi.
You would need to be lucky to do that, having another set identical with the same firmware in would be a fluke. In my experience there are so many variations of flat panel sets it's a nightmare.  Even ones with identical model numbers can be totally different inside

[Refugee]

It would need to be the same panel part number and then the set of boards could have any firmware revision otherwise there is a scrap set lurking.