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

[freakaftr8]

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

both IC'S drive one side and one drives the other I know that this set work off balance for considerable amount of time from what it seems make sure that you're getting proper connections on all pins if ICF1 and ICF2. also you will want to ohm each LED strip against ground to make sure that you're not grounding out especially on the left hand side the bracket that holds the LEDs comes down to a sharp point where the wiring goes into the strip really crappy design. But I almost guarantee that you're shorting out or you have a bad connection

[johnboy1313]

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

I found one strip with a short. I fixed it. All four strips bench test ok. Now I can get three of the four to fire but then they fade after a second.

[johnboy1313]

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

both IC'S drive one side and one drives the other

Is that correct? Both drive one side. One drives the other.

[johnboy1313]

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

At the four connectors for the LED strips, I see 12V, 24V, 12V, and 24V. In that order, when looking left to right from the back of the TV. I'm suspecting one of the driver ICs either failed because of the shorted strip or isn't soldered down correctly.

[freakaftr8]

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

well now you are in my boat. If you remember I'm working on a Haier 42 inch same exact TV. Same problem I replaced all the bad components on the power board but I never check the strips yet. so I powered it up and I had a split second flash. Now that's all it does. I do believe you might have shorted a driver IC with that bad shorted strip. You could check the regulator diodes upon the very top the big ones I forget that socket number but there's two of them you might have shorted one out at least I found one of mine shorted and cracked on the bottom they are right next to the output connectors remember though one strip goes into the other strip so the outer connector goes serial into the inner connector on both sides so if both strips are not working or one shorted it will kill the whole side and if you look at the strips when you power the TV up one will be a little dimmer than the others that's your shorted strip. But if they all ohm with no resistance then I would definitely say one of the IC's have failed again.

[freakaftr8]

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

also those voltages seem rather low. most likely because it doesn't stay powered up enough to see the real voltage

[budm]

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

It should be about 40VDC.
One of my string has shorts to chassis after warm up.
You can also have just one plug in on connector at a time since there is no open LED detection circuit, only over current protection circuit.
I can run mine with just 2 strings.

https://www.badcaps.net/forum/showpo...3&postcount=47

[johnboy1313]

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

Wow bud, you are awesome!

[freakaftr8]

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

for me instead of ordering a power supply I'm going to see if I can locate these two LED driver IC's and replace them again now that I know that all my shorts are taken care of so stay tuned

[budm]

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

Correction: "You can also have just one plug in on connector at a time since there is no open LED detection circuit, only over current protection circuit."
It SHOULD BE ONE PAIR of LED STRING.

[johnboy1313]

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

for me instead of ordering a power supply I'm going to see if I can locate these two LED driver IC's and replace them again now that I know that all my shorts are taken care of so stay tuned

I got four ICs from a U.S. supplier via eBay for $9.27 shipped.

Correction: "You can also have just one plug in on connector at a time since there is no open LED detection circuit, only over current protection circuit."
It SHOULD BE ONE PAIR of LED STRING.

Even if I could get the two side strips to work, I'd be happy.

[budm]

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

@johnboy: I did not take the screen apart so where are the location of the LED strips?
Left and right edge, or top edge and bottom edge?
The two outputs of the power supply should stay on and put out 40Vdc without LED connected.

[freakaftr8]

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

One on each side and two at the bottom. the sides are where the problem is the metal brackets that hold the LED strips on come down to a sharp point on the bottom where the wires go into the LED strips of course the red anode lead is on the bottom right near the sharp angle and it cuts into the wire . under many heat and cool cycles it finally rubs through.

[johnboy1313]

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

Three of the strips have clearance for the wires. Like this (I'm on my phone and can only post one pic at a time.

[johnboy1313]

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

The left side strip doesn't have the same clearance.

[johnboy1313]

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

At the four connectors for the LED strips, I see 12V, 24V, 12V, and 24V. In that order, when looking left to right from the back of the TV. I'm suspecting one of the driver ICs either failed because of the shorted strip or isn't soldered down correctly.

I touched up a bad solder job on one of the LED drivers ICs. Now I see 20V, 40V, 4V (yes 4), and 20V. I'm going to keep playing with it to see if I can figure it out. To be honest, I could live with the backlight as it is if I knew for sure the low voltages wouldn't screw something up in the future.

[budm]

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

When I test the Voltage at the output, when you first turn on the TV, the Voltage is at 20V and then seconds later it jumps up to 40V, I guess it is some kind of soft start in case there is shorted circuit so the current draw will not be too high and cause bad damages.
The reading of 4V looks like where the shorted circuit is.

[johnboy1313]

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

I'll repace that IC and report back.

[budm]

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

If you can get the 40V (using chassis as GND ref) at the Cathode of both Diodes without the LED strings attached an the Voltage stays at 40V without going into shutdown, then you will know the circuits are working.

[johnboy1313]

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

With the LEDs connected or unconnected, 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 (I can't read the label in the pic).