Samsung HL61A750 weird blanking issue

[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 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