Samsung LE32M86BD continuous power cycle

[Th3_uN1Qu3]

Been brought this set today. Owner said it took longer and longer to turn on, it takes around 20 minutes now. In this time, the TV keeps rebooting. The startup chime sounds, backlights light up briefly, sometimes some stripes flash on the screen. Then the process repeats until it finally turns on. During this cycle, sound cuts in and out, but picture doesn't come on. Also, it doesn't take any less to turn back on even if it's only shut down briefly, so this does not look like a capacitor issue to me.

No visible bad caps anywhere, and all voltages are stable and within spec. I noticed that the power supply shut down briefly in between the cycles. I found that the mobo was commanding it to turn off via the standby signal, so i wired that to the 5v standby rail via a 10k resistor to keep the power supply on and cut the signal from the mobo. Now the PS no longer shuts down, but the mainboard still keeps rebooting, and the standby signal goes with it too.

I took off the shield covering the main ICs on the motherboard and still haven't found bad caps or out of spec rails. Other than attempting to reflow the CPU, i've got no other ideas, feel free to chime in.

[vinceroger69]

Re: Samsung LE32M86BD continuous power cycle

do these suffer from the corrupted eeprom issues that some samsungs do? i am sure i have read something about shorting pins 5 and 6 on the eprom?

[tom66]

Re: Samsung LE32M86BD continuous power cycle

I had a similar issue with an LE32N87BD, and I never solved it. I suspect that there's some kind of protection (such as a supply voltage sense, Samsung have undervoltage detection usually) that's misfiring, or as Vince suggested a corrupted EEPROM.

If the caps are samwha, replace them anyway.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

The caps are Sam Young. Heating them didn't give any result, so i'm pretty sure they're not bad. I'll swap some out anyway, but i don't think it'll do much.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Can you check ripple using your scope, on the supply rails?

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Not sure how much it will help but here's the manual for the set:


Looks fairly detailed with scope shots, schematics and troubleshooting flowcharts. Better than the LE32N73 manual so might be more useful for tracking the problem down.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

My current scope only goes down to 100mV/div with a x10 probe, so i won't be able to see much, but i think it might be enough to spot anything objectionable... Anyway, i've left it to power up, see how long it takes.

I had the manual already, but it isn't too much help, at least with the troubleshooting chart... Will look up how much a new main board costs.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Try entering service mode: with power off (standby) on remote INFO, MENU, MUTE, POWER.

Then do factory reset and see if there's an error log anywhere. Also curious how many hours it has. The NEC plasma I just fixed had a little over 10k hours on it which isn't too bad, but not great.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

That is if i get the thing to power up first, left it for over 20 minutes no joy. It's definitely not the tcon as i've unplugged that to get the same result.

I think i've spotted something tho. I've noticed a fluctuating 12v rail on the sub-board (which isn't coming from the mobo, it's generated locally), which normally sits at 12v, drops down to 11.something as the chime is played and the backlights fire up, then jumps to 12.5v just before the backlights shut down and the cycle repeats.

I've pulled the sub board to take a closer look and it seems we've got us a shorted device, reading unusually low voltage drops on 2 of the pins (not 0, but low enough to suspect it). It's a switching regulator of some sort. Going to look it up now.

The set is about 3 years old, we'll see about the number of hours.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Well, I've noticed that the B13V is generally not very stable on Sammys... but it's usually 13.5-14V unloaded, high 12.ish loaded... so it would seem you may have a problem there. I had an LE40A656 which would get upset by less than 11.5V on B13V (bad caps on that.) Actually, on that one, the ripple on the rails was just 50mVp-p when it was bad, with bulging Samwhas. You wouldn't call it bad, but obviously it was.

Also, I've pulled a Sam Young with high 3 ohm ESR (1000uF 10V) but no bulging.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

That device i mentioned is a LDO, and the "shorts" are just resistors... EN/ADJ to ground reads 160 ohms (spotted the resistor itself as well), VOUT to ground reads 47 ohms... Far from a short at the voltages this thing is running at.

I'm now focusing my attention on where that 12v rail is going.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Can you share some pictures? The SM's pictures are too poor for locating components.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

Will do... But hey wait. For one, i'm in error, that rail does come from the mainboard, and in turn, from the PSU.

Second, you said 13v? I swear i thought it should be 12v... Oh yes, there it is, 13v written on the PSU. *facepalm*. Wait a second here... i'm gonna ask those caps in the PSU a few questions.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

Will do... But hey wait. For one, i'm in error, that rail does come from the mainboard, and in turn, from the PSU.

Second, you said 13v? I swear i thought it should be 12v... Oh yes, there it is, 13v written on the PSU. *facepalm*. Wait a second here... i'm gonna ask those caps in the PSU a few questions.

Every Samsung I have seen uses 13 or 14V instead of 12V and the older "LExxM/R/Nxx" uses 13V mostly. I have no idea why. They also like using 5.3V, or 5.4V rails. Perhaps it's to annoy people trying to bodge in ATX PSUs (hah)... someone did that here with an LG monitor with a frigged power supply.

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

Interesting bit, it's also got a low dropout 12v regulator making 12v from that 13v... And yes i've noticed the 5.3v bit too.

Unfortunately, the 13v cap was okay for ESR. Even replaced, no change. Also tried supplying 13v externally. Still the same thing.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

But the 12V is still dropping out? Is the 13V stable? Maybe the regulator is a dud or wounded. No idea why they would use 12V and 13V!

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

The 13v is what's low, and yes, it is stable when supplied externally. The 12v, in this case is... pretty much the same like the 13v.

EDIT: Some careful googling brought me to this thread in French. Google translate makes it pretty hard to understand, but i know a little French, and that guy says that heating the boards with a hair drier got the TV going, and eventually the fix was to replace "the board between graphic card and tcon" which is the sub board. Gonna hit it with the hot air and report back.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

I know about two words in French - "Oui" and "No" ... I'm not sure what that extra board does. Some kind of video processing? I had a 1080p Philips similar to that with a board in between the T-con and main board, called the "1080P BOLT ON MODULE", apparently it converted duplex LVDS into two separate streams. Though, I would expect a failure in that module would leave it with no picture or graphical issues. If the 12/13V is dropping out, the problem is likely on the PSU, unless somehow the boards are drawing too much for the PSU (which seems unlikely... smoke would likely leak out of something when you're talking about a ~1.5A 13V rail.)

[Th3_uN1Qu3]

Re: Samsung LE32M86BD continuous power cycle

Though, I would expect a failure in that module would leave it with no picture or graphical issues.

And, it does. I managed to keep it on by heating the sub board and repeatedly pressing the Source button at the same time. It's all garbled randomly colored horizontal lines, can vaguely see the outline of a menu. Quickly put it into standby and fired up again, et voila, a clean "No Signal" screen and a menu. Put it into standby and fired up a third time, garbled screen again.

Time to take that shield off and reflow the BGAs.

[tom66]

Re: Samsung LE32M86BD continuous power cycle

This is going to turn into another BGA saga, I just know it. Combined with lead free solder I'll bet and it creates a lot of problems.

Maybe I should have tried that with the LE32N73. I'm not sure but I think the RAM was BGA, though the main processor was large pin count QFP.

Come to think of it, a user by the name of Graham on here had a problem with a 58" Samsung plasma not powering up intermittently. He got it working by grill/oven reflowing the board, but it was only temporary and it died again. Board replacement solved it but I wonder how many more have died - I wouldn't mind such a TV if I got one with that fault...!