Samsung LA46F71B hiccuping

[dkneyle]

Purchased as uneconomical to repair. Fault evident shortly after startup. Fail state goes to coloured vertical stripes displayed in defined rectangular blocks, before set goes through a re-boot procedure and comes back displaying the same fault symptoms and goes repeatedly through that pattern.
When I received it and observed these faults I assumed an intermittent connection. I've jiggled and wriggled and have never been able to ever again get the set to start up normally.
I've replaced all the electros on the power board other than the main supply capacitors. I disconnect the T-Con board and the hiccupping remains. The backlights look OK and light up fine before the TV shuts itself down. I've disconnected them and the hiccupping remains.
I'm coming back around to assuming a power supply fault. The original intermittent nature of the fault was suggestive of an easy fix, but not so far!
By the way, it does respond to the remote control. If I select 'menu' I can ses the patterning on the screen change (just before it shuts itself off again).
Anyone want to throw a suggestion into the ring?

[dkneyle]

Re: Samsung LA46F71B hiccuping

I think I've narrowed it down to the mainboard. Remember the old axiom: "the most obvious reason is probably the fault".
I've measured power supply voltages and they all seem OK, and they hold up. I can see the inverter 'on/off' signal line going up and down in sympathy with the inverter switching off; that signal comes from the mainboard. And when I pulled out the mainboard it showed signs of a liquid (coffee?) having being spilled over it. I tried washing it down with methalyted spirits (alcohol) and removed most signs of the coffee but the result was no better. Looking at the board with a magnifying glass I believe I can see a powdery residue that looks like a white/grey oxide sitting between and underneath the legs of many of the SMT ICs.
Anyone want to suggest any radical solutions to see if I can recover this situation? The fact that the TV has shown signs of working intermittently at start up before it dropped into permanent fail mode as I tried to fault find it suggests that it might be recoverable. Is there some alternative product I could soak the board in? I've got nothing to lose. The cost of a mainboard is too high to justify, and I can't see any readily available on the net anyway. (I can see this set going into storage and one day I might come across the same model at the tip and be able to scrounge parts.)

[tw2005]

Re: Samsung LA46F71B hiccuping

Pity you did not take some pictures before you cleaned it. One would have to ask how coffee would get on the board. Could it have been leaking electrolyte?

Going by post one it sounds mainboard and possibly badcaps on the main, maybe on the 5V line.

I had a Jbhifi special which would pop and squeak, screen would freeze then crash with digtal noise, vertical lines of green and red.

That one I found a dry joint on a 100uf cap on the 5v line. That was on the PSu.

have you tried heating the board up at all?

That's my limit of experience with LCD (next to none)

probably not much to gain in these posts , one is bloated with a lot of silly posts

https://www.badcaps.net/forum/showthread.php?t=9651

https://www.badcaps.net/forum/showthread.php?t=9651


http://www.electronicsmarket.com.au/...01-c-1713.html

[dkneyle]

Re: Samsung LA46F71B hiccuping

G'Day again Mate,
Yep, hit it up with a heat gun hoping it might be a dry joint. No joy. It certainly looked more like a spill of liquid rather than an exploding capacitor. And it was brown, and didn't look like rust. The voltages on the Power Supply all seem OK from my preliminary measurements, the 5 volt looked more like 5.5 volts. I've replaced all the electro caps just hoping that would be it. No, I'm pretty sure it's a crook main board.

[tw2005]

Re: Samsung LA46F71B hiccuping

That's our biggest problem over here, no recycled parts. I try and avoid any TV with a suspect mainboard. easier said than done.

did look like a lot of parts may be available at component level for the main, but that would be a challenge and big gamble

[dkneyle]

Re: Samsung LA46F71B hiccuping

I brought back 4 TVs from Sydney so I could have a go at learning to repair them. I thought this Samsung would be the easiest because it was working on start up, then dropping into fault mode. I thought it would be the old capacitor problem for sure. So I got all the others going but this one looks like being a write off. I notice on the web that it sold for more than $5,000 when released onto the market in about 2006. One of the first to have 1080 resolution. Seems sad to see it end its life this way, given that the panel works OK.