Seiki SE421TT,Powers on and off. No picture, no backlights.

[budm]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

"I get 40V across the left cap (CF5), 40V at the left diode (DF4), 24V across the center cap (CF6), 24V at the right diode (DF1), and 24V across the right cap"
Do you mean measure at the Cathode (the silver band on the body of the diode is Cathode) of the Diode?
You should get 40VDC (Using chassis as GND ref) at Diode DF4 Cathode for that power supply, also 40V at Diode DF1 Cathode for the second power supply.
So DF1 power supply section is not right.

[budm]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

OK, I understand now, so yes, you have problem in that DF1 drive circuit section, start checking the diode and caps, you can swap them to see if the problem will follow, those caps in that section get pretty due to the heat form the circuit.
I saw some of the board has two diodes connected in parallel with DF1, DF4.

[freakaftr8]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

I'll be eagerly watching this. My supplies now to the point where it doesn't light up the LED strips at all all the sudden. Before it would flash abruptly upon power up but now nothing

[johnboy1313]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

Well, I replaced the driver IC and double checked the mosfet and the diode and nothing changed from my last post. I'll poke around a bit

[johnboy1313]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

I found a used board for less than $35 on a site called bonanza.com. I figured it was worth a shot so I pulled the trigger. It showed up today, I installed it, and everything seems to work correctly. On this power supply, I have (from left to right) 20V, 40V, 20V, and 40V. All three caps below the LED connectors and both diodes show 40V. Like I said, it seems like everything is working.

[budm]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

That is the same Voltage readings as my TV, glad to hear you get it running again.

[johnboy1313]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

I'm going to try to use this PSU to get the other PSU working, install the other PSU once it's working, and see if I can sell the good one on eBay.

[johnboy1313]

Re: Seiki SE421TT,Powers on and off. No picture, no backlights.

I found a broken trace between the driver IC and the series of strips that weren't working on the bad PSU. I soldered a jumper in, now I see 20V, 40V, 18V, and 35V. I see 35V at that diode and cap as well. There is some mild flicker in the backlight. I'm guessing the flicker is due to the low voltage. I broke a few traces from that IC when I pulled the original. I "fixed" the broken traces with jumpers. The jumpers are pretty close to the same length as the broken traces. One is slightly longer than the trace. I can't find anything else wrong with this board. Is it possible that the longer jumper would cost me 3-5V? On the good board there is no resistance between the pads with good traces. On the bad board there is no resistance between the jumpered pads. Any thoughts?