TV flicker at start up

[DIYspanner]

Technika LCD 32-270

The TV is usually left on standby. When switched to ON, the screen flickers for about a minute then settles to a good picture.

Loose connection effected by circuit warm up perhaps?

Comments on a fix very welcome.

 

[Harry Bloomfield]

Have you tried tapping the set, to see if you can reproduce the issue. Most sets, take a while to fully boot up, might it be still booting up?

 

[DIYspanner]

I've got an Hitachi brand and that has a steady picture at startup.

What I know about the Technika is the flickering started in recent months. I tried switching on from the wall with all accessory cables unplugged but still got the initial flicker.

Noted about the tapping test. Will investigate further.

 

[Harry Bloomfield]

Noted about the tapping test. Will investigate further.

If that proves positive, then it could be an easy fix for someone with the skills.

 

[DIYspanner]

Hunting around, I found this article about capacitors in the very same TV.

I took the back off and found three capacitors with a slight bulge so perhaps the culprits?

 

[Scally-Ho]

If a capacitor had failed, then IMO the flicker would not have stopped after a few minutes. Although the flicker must be in some way heat dependent which indicated to me there is a dry joint somewhere that closed up as the set's temperature increases.

 

[Harry Bloomfield]

I took the back off and found three capacitors with a slight bulge so perhaps the culprits?

Those definitely need to be replaced, irrespective of whether it fixes the problem..

 

[DIYspanner]

If a capacitor had failed, then IMO the flicker would not have stopped after a few minutes. Although the flicker must be in some way heat dependent which indicated to me there is a dry joint somewhere that closed up as the set's temperature increases.

Perhaps the capacitor circuit only works when the TV is booting?

I'll get the capacitors replaced. Perhaps one of them have a dry joint.

 

[DIYspanner]

These caps are the same spec stated in the article I quoted above.

Are they suitable replacements?

 

[Harry Bloomfield]

These caps are the same spec stated in the article I quoted above.

Are they suitable replacements?

They are the same type, electrolytic, so that part is fine, as is the style. The other two things to watch for are the voltage, which must be the same or higher, and the capacitance value, which must be exactly the same as the originals.

Note they are polarity sensitive, so must be inserted the correct way round.

 

[DIYspanner]

I've checked and the caps in my TV are the same spec as those in the article. 35v 470uf

I've also noticed that the PCB the caps are mounted on is marked HOT and COLD, the faulty caps being on the side marked COLD.

 

[Harry Bloomfield]

I've checked and the caps in my TV are the same spec as those in the article. 35v 470uf

I've also noticed that the PCB the caps are mounted on is marked HOT and COLD, the faulty caps being on the side marked COLD.

I can't say I have ever seen that before, my best guess is it refers to the mains input side, live - hot, and the low voltage side - cold

 

[DIYspanner]

Searching ebay, I found this listing sold by seller who's worked in the electronics industry. Having sent them a photo of the caps in the PCB, they claim the ebay listing are a premium brand and more reliable compared to the brand already installed.

I asked them about the HOT and COLD marking on the PCB.
I quote their reply,
"
HOT represents all of the high voltage side of the board, and COLD, the 'safe' low tension voltage side of the board. You see in your photo, the small 4 legged Optoisolator bridging between the high voltage and low voltage side of the board, this allows the low voltage side of the board to give control signals back to the high voltage side, without electrical connection, its done by light inside the optoisolator.
"

 

[freddiemercurystwin]

Once (if) you fix it something else will probably go wrong, could buy another TV for £20 or even get one for free off Marketplace, bonkers.

 

[Harry Bloomfield]

HOT represents all of the high voltage side of the board, and COLD, the 'safe' low tension voltage side of the board. You see in your photo, the small 4 legged Optoisolator bridging between the high voltage and low voltage side of the board, this allows the low voltage side of the board to give control signals back to the high voltage side, without electrical connection, its done by light inside the optoisolator.

Exactly as I suggested then.