Samsung HL61A750 weird blanking issue

[YamahaFreak]

(I'm surprised there isn't a board dedicated to rear projection TVs, now that I think about it.)

This is a weird one. I LOVE this TV, I saved it from the curb many years ago when it needed its DMD replaced (did it myself) and it's been in pretty much constant use since. It's just turned 16 years old and I recently had the blue LED go out, so I went ahead and replaced them all. The issue is unrelated. This ONLY happens on the component video inputs, NOT over HDMI. When I am playing games or watching TV and a scene happens that makes most or all of the screen white or very bright (white screen, flashes, explosions, etc.) the TV will just...drop the signal. I temporarily lose video and audio until the onscreen image darkens back down again. It's as if someone changed the video input (OSD appears briefly once the set regains its footing). If the screen remains bright for long enough, I actually get the 'Mode Not Supported' dialog...very puzzling. I didn't think that would display unless I'd connected something with a resolution the TV couldn't handle? (E.g. feeding a 4K/2160p signal into it) The Wii U game console I have plugged into the component jacks is outputting 1080p and otherwise is just fine, no issues unless and until the screen suddenly gets bright. I'd previously been using the same game console on an HDMI input and had no issues. I moved it to component because I needed the last available HDMI port for a new Roku Express streaming stick.

Anyone have any thoughts on why this could be happening? If needed, I can try and reproduce it and video it.

[JohnCT]

I had a Samsung DLP (lamp type) do exactly that, but I don't remember what I did to fix it..

I seem to recall we didn't fix it because of the cost of the board. We had eliminated the DMD board IIRC and I *think* we had identified the main as the cause. Sorry I can't be of any more help than that.

John

[old_tv_nut]

Wild stab: something involving sync separation that goes bad when the average video level is high? A leaky or open cap somewhere in the sync circuit?

[YamahaFreak]

Originally Posted by JohnCT

I had a Samsung DLP (lamp type) do exactly that, but I don't remember what I did to fix it..

I seem to recall we didn't fix it because of the cost of the board. We had eliminated the DMD board IIRC and I *think* we had identified the main as the cause. Sorry I can't be of any more help than that.

John

No need to apologize! Any insights are welcomed.

[YamahaFreak]

Originally Posted by old_tv_nut

Wild stab: something involving sync separation that goes bad when the average video level is high? A leaky or open cap somewhere in the sync circuit?

I'll go on the hunt for bad caps next, thanks!

[JohnCT]

Originally Posted by YamahaFreak

I'll go on the hunt for bad caps next, thanks!

One thing about bad electrolytics - most of them can be ferreted out with heat - they love the heat and hate the cold. Try heating one board at a time and see if the symptom improves or the problem goes away. These years of Samsung DLPs did have bad caps. There were a couple right on the DMD board that would cause either no start or intermittent shutdown (the smd "fish" caps). I'd heat the DMD board and if the projectors ran OK, I'd change the caps (lower right corner IIRC).

I used to heat boards and if the board improved, I'd put the board in the refrigerator for an hour then go over it with an ESR meter.

If you can access the boards and run them live, use your scope and look for noise on the positive side of every electrolytic. If you find noise, check the neg side to make sure it's not a floating ground. If the cap is grounded and has a high noise signal, it's bad.

John