PN42B450 No Video

[war6763]

Good evening everyone!

I'm working on a Samsumg PN42B450 42" TV and I'm stumped. I can't figure out what's going on with this TV; here's what I've done:

• Tested the Y-Buffer PCB. No shorts or burned components.
• Tested the main power board. All voltages correct, trimmed, and present. Powering off the TV kills the PSU, turning it on causes all voltages to stay steady.
• Tested the Y-main board. No issues with voltage, no shorts on the ICs connected to the heatsink, caps all look good. No shorts.
• Tested the X-Main board. No issues with shorts on ICs or Caps, no shorts, etc.
• Tested the main board, LED blinks properly, all connectors in good, properly seated condition. Running the test pattern yields no image.
• Tested all fuses, they're all good!!

All the capacitors look good, no components are burned or show signs of dying, etc.

One thing to note, the screen will sometimes start showing an image for a split second. Sometimes because I was moving a capacitor or tapping on something on the Y-Main board. This may have also been a fluke.

If you look at the screen while activating the menu on the remote, you can see a change in the "black" screen. It becomes slightly lighter. I'm also not sure if invoking the screen test by shorting pins 3 and 4 on that connector on the Main Board should also produce sound. If it should, then I can't hear anything!

Please let me know what you guys think!!

[war6763]

Re: PN42B450 No Video

Can I get a mod to fix the title? I goofed and didn't add the make.

[capkid]

Re: PN42B450 No Video

You mentioned that the LED is blinking normally. Did you mean the logic board's LED? Did you check for bad solder joints?

Regarding test patterns, is the test you performed? https://www.badcaps.net/forum/showpo...61&postcount=2

[war6763]

Re: PN42B450 No Video

You mentioned that the LED is blinking normally. Did you mean the logic board's LED? Did you check for bad solder joints?

Regarding test patterns, is the test you performed? https://www.badcaps.net/forum/showpo...61&postcount=2

That's right, the logic board's green LED is blinking at about 1Hz. I checked the Y and Z boards for cold solder joints.

[tom66]

Re: PN42B450 No Video

Any subtle glow from the plasma panel in a dark room?

[war6763]

Re: PN42B450 No Video

Any subtle glow from the plasma panel in a dark room?

There is! The glow will also change when I press the "menu" button on the remote!

[capkid]

Re: PN42B450 No Video

How is your VE voltage on the X-main?

[tom66]

Re: PN42B450 No Video

It could be a control board issue...

[capkid]

Re: PN42B450 No Video

Yeah, it appears to be either the X-main or the control board. The fact that you have no test pattern onscreen, if the test was performed correctly, and the LED is blinking normally seems to point to a bad control board. I'd still check the VE on the X-main.

[war6763]

Re: PN42B450 No Video

Yeah, it appears to be either the X-main or the control board. The fact that you have no test pattern onscreen, if the test was performed correctly, and the LED is blinking normally seems to point to a bad control board. I'd still check the VE on the X-main.

On this particular model VE comes from Y-Main directly, and measuring that on the board is 90V (as expected), at least at the connector.

I've been suspecting the control board as well.. Let me get one on order and I'll get back to you guys!

[tom66]

Re: PN42B450 No Video

Even if X-main were bad completely you'd still get a partial picture unless control board gets confused by a bad board and stops driving panel properly.

[war6763]

Re: PN42B450 No Video

No dice. I just installed the replacement control board and the TV is doing the same thing.. Anything else you guys might recommend?

[war6763]

Re: PN42B450 No Video

Can anyone help me find some test points to look at with the scope? I would love to figure out what's wrong with this TV..

[jjanssen7]

Re: PN42B450 No Video

I have the exact same TV with the exact same symptoms. If there is anything you want me to look at mine to help you with a solution let me know!

[war6763]

Re: PN42B450 No Video

I should also point out that the "screen glow" is no longer present after replacing the board. Also, the Z-sustain board is VERY loud. Maybe that has something to do with why I still can't get an image on this TV?

[jjanssen7]

Re: PN42B450 No Video

Maybe Tom has some advice, all I know is that mine has the exact same symptoms (have done the same tests as you)... I have not replaced my control board, but If you Google the board number and dig a little there are others out there that feel this control board might be suspect after testing as normal y & X boards. How sure are you that the control board is good?

[tom66]

Re: PN42B450 No Video

Can anyone help me find some test points to look at with the scope? I would love to figure out what's wrong with this TV..

What scope do you have?
Do you have a 10X 400V probe available?

[war6763]

Re: PN42B450 No Video

What scope do you have?
Do you have a 10X 400V probe available?

I've got a 500MHz scope with a couple of 100, 400, and 1kv probes.

[jjanssen7]

Re: PN42B450 No Video

WAR6763, where you able to get anywhere with this symptom?

[tvtimmy]

Re: PN42B450 No Video

I had one that had screen glow. It turned out to be a blown fuse on the E or the F board.