Samsung HL61A750A1FXZA LED DLP TV repaired

[james_s]

My mother's Samsung TV croaked the other day, this LED DLP set is almost exactly 10 years old but still in good shape. Worked in the morning then she turned it on later and the red LED would blink but the screen never lit up.

Pretty quickly discovered that the 16V DC-DC converter that powers the light engine had no output. The main converter IC as well as a small SMPS IC that provides power to that were both dead, 33 ohm fusible resistor open. I replaced the ICs and powered it up on the bench, output looked good. This board takes ~380VDC in and puts out 16VDC at a good amount of current. Seemed good so I put it back in the TV, hit the power button, BANG! The little IC and the fusible resistor exploded, main converter IC also checked bad again. Did more poking around, discovered that the main bulk filter capacitor was completely open, desoldered it and a pin fell off. I replaced that and replaced the ICs and resistor again, this time the TV powered up and is working fine again.

Apparently what happened is with the bulk filter capacitor doing nothing, the inductance of the 3 feet of wires between the DC source and this board formed a boost converter that exceeded the max rating of the IC. Should have tested all the capacitors to begin with but it's rare that I find a big bulk filter to be bad. Anyway with a little luck this thing will go another 10 years.

[highdesert56]

Good info, thanks for sharing.

Isn't that fun when things test good on the bench only to blow up when put back together?

At least it didn't take even more stuff with it.