Samsung LED Monitor (S27B350H) -- Bizzare Failure!

[wraper]

As TerraHertz said, he suspects the issue is to do with the video processor not corrrectly synchronising to the input video waveform, specifically not extracting the timing pulses. They normally use something called a Phase Lock Loop to adjust a local oscillator to synchronise with the incoming signal.

Doubt that, monitor's own OSD on the video is exactly the same.

[Obsidian_ShadowHawk]

Hi

Randomly changing components may, or may not, fix the problem.

Good engineering practice is to find the root cause and fix that.

Wow, glad to hear someone can back me up on this!  I will not change components unless I'm have diagnosed it beyond a shadow of a doubt. Throwing parts at the problem is bad practice--can you even call that "troubleshooting"? If I did that at work (airframe mechanic) I'd be fired on the spot.  The definition of troubleshooting is performing tests and making observations to narrow down the cause of the problem.  Not to mention that my sub-par soldering skills and equipment will probably make EVERYTHING worse if I'm try to hack off every cap on the board. Haha. I'm will need to spend alot of time on a practice board before I feel comfortable changing components like this.

Anyway, I'm could not find any data on the two main chips. The one is a proprietary Samsung Magic Color part, and the other chip only appears in the block diagram of the LCD panel datasheet (manufactured by CMO). The only pin out I have to work with is for the standard LVDS cable, and some labeled teat pads on the bottom of the board (thanks Samsung!) :
Also, when in the failure mode, the high pitched buzz noticrd in the video I definitely coming from one of the chip-on-flex parts at the top edge of the panel, on the left end, not the main CPU board as originally suspected.

I got better pictures of everything last night, will post them when I get back to my comouter (at work now).

if the problem disappears after a time, the first thing I would do is to grab a can of ice spray and use it to spot the problem source.

Good idea, and I did try that a few times. But two cans of spray every way i could think of got me nowhere.

[CJay]

Totally agree with Mosher, good engineering practice is to diagnose a fault based on evidential means.

But, and this is a big one, experience can play a huge part in diagnosis of any fault.

You are, in essence, applying the benefit of that good engineering practice from the past to the current 'patient' from accumulated memory.

If you've spent 30+ years repairing electronics, you  develop a sixth sense for faults, that 'gut' feeling is not just a wild guess, it's based on the accumulated experience of diagnosing things by attaching test gear and understanding how electronic items work.

TerraHertz used exactly that experience to make his suggestion, my suggestion that it could be capacitors is likewise based on my experience of repairing consumer goods (and some really rather expensive non consumer hardware).

Good clean power supply rails are incredibly important and the main cause of power supply problems are failing capacitors.

The order of fault finding is always ensure power supplies are good, check reset lines and clock signals.

After you've verified all those are in good order then you can proceed into the more esoteric areas of the design.

[MosherIV]

CJay Sorry if I got the wrong end of the stick. It looked like the OP was being encouraged to replace every cap on the TV.

I agree completely about making sure the PSU is working correctly.

Not sure what can be done if documentation is not available. Maybe trace the video signal to the big ASICs. Need to then check with scope what is coming out of the ASICs. Hopefully, there will be something that is the same freq as the line or frame/field and shows jitter.

What do you think CJay?

[CJay]

CJay Sorry if I got the wrong end of the stick. It looked like the OP was being encouraged to replace every cap on the TV.

I agree completely about making sure the PSU is working correctly.

Not sure what can be done if documentation is not available. Maybe trace the video signal to the big ASICs. Need to then check with scope what is coming out of the ASICs. Hopefully, there will be something that is the same freq as the line or frame/field and shows jitter.

What do you think CJay?

Well with some pieces of equipment the cost of capacitors and the need to remove them from circuit to test them means testing by substitution is more economical than the time taken to remove test and refit so it makes sense to replace them wholesale, they're essentially a 'wear part' at that price point, while it's not 'educational' it is a valid troubleshooting method.

Chances are also that if one has shuffled of it's mortal coil then the others are likely to be on their way too.

When the caps are something 'special' (high voltage, high cost, non-stabndard etc.) then of course it doesn't apply.

 Consider the whole monitor  assembly as the airframe and the capacitors as the bolts or rivets (or whatever 'must replace' parts are on an airframe) holding bits onto it to place it in the OP's frame of reference.

Tracing an LVDS signal isn't going to be easy, could be hundreds of megabits per second but it should be possible to trigger on some combination of the clock signal, frame or line sync and at least see the jitter.

Working out why is another matter entirely if the basics I outlined don't fix the problem.

I'd be reading LCD panel application notes if I were more interested in troubleshooting this sort of fault.

[Rasz]

I suspect randomly changing capacitors will not fix the issue, but I wait to hear your results.

just listen to the clip, its nor random