Sceptre X42GV-KOMODO, sound but NO PICTURE

[Paul678]

Ok, I picked this unit up. All marked DC voltages on the power
supply check out good, and no bulged caps or any sign of damage
on the power supply. On/Off switch toggles the red/blue LED
indicator on the front.

A healthy +24.8 Volts is reaching both inverter boards (they are Inverter Board 4H.V1838.371/C2), but after
cautiously checking for an AC voltage on the primary side of the
high voltage transformers, I found absolutely nothing on either
board, so clearly nothing is getting to the CCFLs.

Both the "M" board (on left side of tv, while viewing from back)
and the "S" board have 14 pin ribbon cables, which have no voltages
on them except a +1.3V on pin 13 of M, and a +1.3V on pin 2 on S.

Shouldn't the inverters automatically turn on when the TV is powered
up? Or are they waiting for a "turn-on" signal from the main board,
through the ribbon cables?

Maybe these inverters are good, and it's the main board that is defective?

Any help greatly appreciated.....

[PlainBill]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Usually the inverters are controlled from the main board; the main board ALWAYS controls the brightness and usually turns them on and off.

Pictures of the inverters help us help you. Usually the On/Off and brightness signals come in on one of the power cables. The 14 pin ribbon cables synchronize master and slave inverters.

PlainBill

[tom66]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

"4H.V" part number sounds like a Darfon. Very typical of these for the inverter transformers to go open circuit, but that usually causes two seconds to black. There are also several fuses on the Darfon inverter boards, so check them too. 24.8V is a high side 24V (but still fine, the maximum rating for most of these boards is around 25.5V.) Might drop a bit under load.

[Paul678]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

"4H.V" part number sounds like a Darfon. Very typical of these for the inverter transformers to go open circuit, but that usually causes two seconds to black. There are also several fuses on the Darfon inverter boards, so check them too. 24.8V is a high side 24V (but still fine, the maximum rating for most of these boards is around 25.5V.) Might drop a bit under load.

Yes, this is a Darfon, and here is the Master board:




On the power connector in the second picture, assuming pin1 is on the left,
there is a +4.5V on pin12, and a +3.3V on pin 13, that both come on after
a delay of about 4 seconds after I press the On/Off button. Hopefully
these are the "turn-on" signals, because.....

......in about the center of the second picture, there is a fuse labeled
F1, with a big "D" on it, that is completely open! (I'm trying not to
get excited here....) All the other fuses have a big "TP" on them, but
all these are fine.

Additionally, on the slave board, all the TP fuses are good, but the
one "D" fuse (also labeled F1) tests at about 1 Ohm (my meter shows about 0.3 Ohm when shorting the test leads), which may show a fuse that is going
bad.

If I wanted to temporarily solder fuses to both F1s, what current and voltage rating should I use? Fast-blow, right? I'm sure surface mount replacements
would be expensive from Mouser.....

Thanks for any advice....

[PlainBill]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

It looks like you are doing fine. 'D' indicates it is probably a .25 amp fuse. That certainly isn't handling the drive power, it's got to be for the control circuitry.

PlainBill

[tom66]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

When probing SMD fuses, the solder coating makes it kinda hard to probe sometimes, giving a higher than expected resistance. Fuses, unless poorly designed -always- fail on or off, never half on half off. Whilst it wouldn't be the first time counterfeit parts have been found in TVs, Darfon inverters are generally pretty good (including using high quality capacitors.)

If that powers the inverter control, nothing will happen. Could have failed due to thermal stress - common on LCD T-cons.

I would use a 0.5 - 1 amp automotive fuse, if they even exist. I haven't seen ones below 5 amps.

[Paul678]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Ok, jumpered F1 with a 1/2 A pico fuse, and......

The lamps turn on, "Analog Channel 2" shows snow briefly.....
and the Goddamned screen is CRACKED!!!!



F*$@!!!! ARRGG!!!

Ok, it's possible the seller didn't know about this, because he
was selling another TV which he admitted had a cracked screen,
so I don't know why he would have lied about this one. It's
possible his little kid (who was running around when I bought
it) smashed into the screen during the 6 months it's been
dead. Plus he sold it to me out of his house, so this leads
me to believe it's possible he didn't know about this. When
the lamps are off, the cracks are invisible even when
using a flashlight on the screen.

Let this be a warning to all would-be repair people. This
is why you should buy most broken tvs like they are trash,
because that's what most of them are.

Ok, but as I paid $15, I can still make some cash on Flea-Bay,
as an inverter set went for like $75, and I still have the main
board, T-con, and power supply.

I hate Ebay, as I've gotten my first 2 negative feedbacks, but
where else can you go to sell this kind of stuff? Craig'slist
is too local......

oh well, thanks to Tom and Bill anyways...... haha

[tom66]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Yeah, I'd guess that they wouldn't lie about that, it would be rather strange for them to blow that fuse deliberately, rather than just pull the fuse out of the plug or something.

I got a negative on eBay but I just shrugged it off. Sold quite a few TV parts, but first time selling equipment, in that case it was a variac.

Even broken, a big screen LCD can sell for $50+ but that's on eBay.

[Paul678]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Ok, well I have one more question:

When I turn on the TV, it's mainly black with colored
vertical lines. Then the "Analog Ch. 2" shows up for
a second, followed by actual TV "snow" in the background.
But after a few seconds, it goes back to the black background.

Why doesn't the TV "snow" stay on longer? Does
this mean the main board is also having problems? Or
is the main responding properly to the cracked screen?

I'd just like to know if I have to sell the main board "as-is"
and "for parts only" on Ebay.

[tom66]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Ok, well I have one more question:

When I turn on the TV, it's mainly black with colored
vertical lines. Then the "Analog Ch. 2" shows up for
a second, followed by actual TV "snow" in the background.
But after a few seconds, it goes back to the black background.

Why doesn't the TV "snow" stay on longer? Does
this mean the main board is also having problems? Or
is the main responding properly to the cracked screen?

I'd just like to know if I have to sell the main board "as-is"
and "for parts only" on Ebay.

No, I expect with no signal it stops displaying snow. Some TVs go blue, some go black.

[Paul678]

Re: Sceptre X42GV-KOMODO, sound but NO PICTURE

Ok, thanks.

E-BAY TIME!!!