Samsung LE40A656 random restart mystery ???

[tn245]

Hi there. I got this TV originally with one swollen cap on the secondary of the PSU. Changed it and its friends for some nice Panasonics and sent it on its way. About a month later it came back to me as it was randomly restarting.

Often after about 15 minutes - though sometimes it can go hours - it shuts off and then immediately comes back on.

• Tried a hairdryer on all the boards and couldn't trigger the problem. Checked and retouched soldering on the PSU with no effect. Tried a factory reset.
  
• Have replaced main board, and then PSU and still the problem persists.
  
• Wiggled all connectors to see if I could make it do it. Nothing I do seems to trigger it.
  
• It doesn't play the melody when it shuts down, though it does as it starts back up, which rules out the buttons and remote sensor. Plus I have tried it with those disconnected and still it restarts.

I can't imagine it would be the backlight inverter board or the t-con as those would result in no picture and not a restart. So what could it be?

Did I coincidentally get a replacement main board/psu with the same problem?

I don't really know how to troubleshoot this as it happens so randomly and quickly that I don't know how to catch it happening.

Any ideas would be very welcome as it's doing my head in and I would like to see the back of it.

[dick_barton]

Re: Samsung LE40A656 random restart mystery ???

I am not 100% certain that this is the correct firmware file but I'll attach it in the event it may be. There's more information at:-

https://www.avforums.com/threads/sam...update.936598/

where they refer to a file of the same name once you unzip and run the exe file.

[dskall]

Re: Samsung LE40A656 random restart mystery ???

Hard to pin down. you will probably have to monitor power supply and mainboard voltages and see if any go out of spec. or vary. Strange that a power or mainboard did not fix it.

[tn245]

Re: Samsung LE40A656 random restart mystery ???

Thanks! I did successfully apply the software update as suggested by dick barton. I haven't seen it restart yet but will keep watching it.

It is hard to pin down as it's unpredictable when it's going to happen so not sure how I would monitor it besides sitting watching it with probes attached waiting for it to happen. I've got better things to do.

Just don't get how the problem persisted with different boards. Wouldn't be surprised to get a bad board from ebay but not one with the exact same problem which doesn't seem to be a common one.

[cliff_hootarski]

Re: Samsung LE40A656 random restart mystery ???

If the updated firmware doesn't fix it, take a picture of the back of the mainboard. Perhaps this has the dreaded C102 problem since it is a "A" model TV.

[tn245]

Re: Samsung LE40A656 random restart mystery ???

No resets so far since the software upgrade. Hopefully that's done it. No C102 on this one. All the parts have 4 digit codes and I can't see any similar cap.

[dskall]

Re: Samsung LE40A656 random restart mystery ???

Well I suppose if it was a firmware issue both boards could have the same problem with the same firmware version. So you could update old board and have a good main and power board.

[tn245]

Re: Samsung LE40A656 random restart mystery ???

Yup, I did update both boards and it seems stable on both, so got good extra boards which is nice.

[tn245]

Re: Samsung LE40A656 random restart mystery ???

Well it was all going so well. Had it running all morning today but then this afternoon it did reboot once. So I guess not as solved as I thought. No idea what to do now besides trying another main board maybe.

[dskall]

Re: Samsung LE40A656 random restart mystery ???

What is voltage on main cap while on? Have you tried heating inverter and t-con boards?

[tn245]

Re: Samsung LE40A656 random restart mystery ???

391V on main cap. I did try heating inverter and t-con and got no effect. Is there a way inverter or t-con could cause a full restart on this model? I figured an inverter issue would only shut down backlight circuit not the whole TV, and t-con likewise would just cause no image or bad image and wouldn't restart the TV. Or is there a fault detection system that would restart it?

It doesn't appear to be heat related. If it was I would expect it to happen more frequently once TV has warmed up and it has happened once, but it seems totally random.

[dskall]

Re: Samsung LE40A656 random restart mystery ???

Well seeing as you have replaced power and main board you either inherited the same problem, possible. Or it is on a different board. I have heard of wifi module causing problems, or button board. So at this point nothing is off the table

[tn245]

Re: Samsung LE40A656 random restart mystery ???

It runs with sound playing with all boards except psu and main unplugged. So I'm thinking to leave it running that way for a while. If it doesn't restart it doesn't conclusively prove anything I guess, but if it does do it it means it's in the main or psu and I just got unlucky with the replacement. Conceivably it could also be a connector or cable issue but I have given them a good wiggle test and haven't triggered it.

[tn245]

Re: Samsung LE40A656 random restart mystery ???

So, guess what.. turns out it was the t-con. Ran it as I said with combinations of t-con, inverter, or both unplugged over the course of several days and the only time it did restarts was when the t-con was in the mix. I didn't think that was possible but at one point I did remove the lvds cable while it was on and it triggered a restart, so the main must reboot the TV when it loses connection to t-con. Got a replacement t-con in and all seems good so far.

[dskall]

Re: Samsung LE40A656 random restart mystery ???

Well could be bad connection on lvds cable was intermittent

[tn245]

Re: Samsung LE40A656 random restart mystery ???

Could have been. My test for this was to wiggle the connectors and cable a lot to see if I could trigger it. Nothing happened. Only restarted if connector was unplugged. If I get another same model in I'll put this t-con in for a while and see if it does the same thing.

[Davi.p]

Re: Samsung LE40A656 random restart mystery ???

14 posts to arrive at the tcon.. mmmh ...some logic holes here...
12v input on the tcon is near directly connected to psu, if a semiconductor goes short with the heat (semi-short) psu goes in protection, much probably there is a power mosfet or power diode, 'cause tcon main processor and others runs from a modified voltage that comes from a protected dc-dc converter, or... since you said that tv restarts when you pull lvds, also a tcon main chip can be a culprit, it goes short, dc-dc goes in protection, i2c communication stops on lvds cable and tv restarts.. who can say it?

[dskall]

Re: Samsung LE40A656 random restart mystery ???

14 posts to arrive at the tcon.. mmmh ...some logic holes here...
12v input on the tcon is near directly connected to psu, if a semiconductor goes short with the heat (semi-short) psu goes in protection, much probably there is a power mosfet or power diode, 'cause tcon main processor and others runs from a modified voltage that comes from a protected dc-dc converter, or... since you said that tv restarts when you pull lvds, also a tcon main chip can be a culprit, it goes short, dc-dc goes in protection, i2c communication stops on lvds cable and tv restarts.. who can say it?

Hindsight is 20/20

[tn245]

Re: Samsung LE40A656 random restart mystery ???

14 posts to arrive at the tcon.. mmmh ...some logic holes here...
12v input on the tcon is near directly connected to psu, if a semiconductor goes short with the heat (semi-short) psu goes in protection, much probably there is a power mosfet or power diode, 'cause tcon main processor and others runs from a modified voltage that comes from a protected dc-dc converter, or... since you said that tv restarts when you pull lvds, also a tcon main chip can be a culprit, it goes short, dc-dc goes in protection, i2c communication stops on lvds cable and tv restarts.. who can say it?

Interesting. Wish you'd been around a bit earlier to chip in. Could have saved me some time.