TV repair?

[chart75]

Hi all, I've been trying to repair my folks TV, with no multimeter or oscilloscope. The picture is blinking on/off, and it seemed to be exacerbated when other appliances are on in the house. I therefore assumed a pose issue, so opened it up and lo and behold, one cap was bloated, so I replaced all the caps except the large filter cap in the centre. Issue hasn't stopped. Anyone got any idea of anything else I could try? Model is a samsung LA40F81BDX/XSA, which has a common issue with caps, so maybe replacing the big central one is worth a shot? Despite no bulging. Thanks! -Chris.

[chart75]

I also should mention its been repaired before, last time they paid for a technician to come out he said that the issue was 'a computer in the tv that didn't know if it was turning on or off', gave me a good chuckle, but in any case one of the caps had been replaced before (which is what i think the tech actually did last time, and asked for the small sum of $250 to do). Has anyone come across anything like this before at all? Such a shame to throw away a good panel.

[BurningTantalum]

I did an LA32something many moons ago. The PSU caps brought it back to life but the backlight was blinking on and off. Can you still see a picture during the 'off' periods? Shine a bright torch across the screen and peer closely.
BT

[chart75]

Hey BT, that's exactly it, the issue is probably the backlight. The image does seem to stay and the menu doesn't pop up after every 'off' session either so I think you're absolutely right. Did you manage to fix the backlight?

[fable]

Does it have led backlight or ccfl ? if it is ccfl you should check caps on inverter board.
Sorry for my bad english.

[chart75]

Hi Fable! Thanks for the suggestion, I've had a look at the inverter board (Pics to come once I've figured out how to compress the darn things) Though the SMD caps on it all look okay (Tell me if you don't think so, I'm definitely no expert) and there doesn't seem to be any throughole caps. Any other suggestions?

Thanks again!

[Srbel]

Could be dead fluorescent tube. But, if there are more then one, than I don't think it is likely for all of them fail at the same time, so it is the inverter. Or maybe the tubes are old, and are tripping the protection in the inverter.

[chart75]

Thanks Srbel, think it's worth trying to replace the whole board?
Pictures finally attached but I think the compression has killed them anyway.

[Srbel]

It could be old backlight tubes. If it is easy to access them, you can at least see if there are black marks on their ends.

In TV they are much thinner, but those black marks look like this: http://cdn1.tmbi.com/TFH/Projects/FH08SEP_REPBUL_01.JPG

[chart75]

Thanks again Srbel, I don't think the tubes themselves will be easy to access (Looks like it'll take totally dismantling the darn thing), I think it might be best to just pick up an inverter off ebay for ~$15 before I go to those kind of lengths. Thanks so much for the help guys! Really appreciated!

[Srbel]

Oh, well if it is not expensive, and you don't have time to troubleshoot, then go for it.

[BMack]

Before you replace the inverter you'd probably be better off to borrow or buy even a cheap DMM to make sure the voltage going into the inverter is good. Voltage going into the inverter should be 24v DC. Do not check voltage elsewhere on the board. If the voltage is steady, replace the inverter. If the voltage is low or pulsing, unplug the inverter and check the cable going in, if it's stable, replace the inverter. If it's still low or pulsing without the inverter plugged in, replace the power supply.

Do you hear any buzzing coming off the inverter?

[BurningTantalum]

Sorry for the delay-
I cannot recall what the fault was in the end. I obtained a replacement scrap inverter PCB that turned out to be totally inoperative. I seem to recall replacing an inverter chip (BA something) after replacing some caps and cobbling up a potential divider to identify the fault but can't remember if it was on the original board or the scrap one.
I found a manual for the LA32M61 quite easily and it may be fairly similar if the LA40 is not available.
Beware high voltage on the outputs of the transformers (1600V ?)
Regards, BT

[Gyro]

Before messing with the inverter board you should take the basic step of checking the power supply. If one capacitor has already been replaced then there could well be others on the way out. Check the power supply caps related to the backlight inverter supply for bulged or split tops (check them all actually!).

This step seems to have been missed (explicitly anyway) from previous replies. 

[BurningTantalum]

Agree with Gyro.
In my previous post I mentioned 'inverter chip'- I meant comparator chip, sorry.

BT