Samsung SP-P4231 "Sparkles"

[iam87x]

Hey everyone! Was hoping someone could help me with my Samsung. Here is my original post on reddit to detail my issue,

Got the above listed tv for free and thought it would be perfect for in my daughters room for the Wii we are planning on getting her for Christmas. When I turned it on the screen was almost completely blue with scattered pixels, Not dead as they were moving around. The TV was responding to inputs as I plugged in my laptop via VGA and got a clear display from the laptop, but was still receiving random pixel issues across the screen. The menu created most of the issues, maybe something to do with the brighter colors being used or something (my background is black on my laptop). I couldn't find a service manual online, but I teach electronics for a living so, I felt safe opening up the back and taking a look for bad components. I didn't see any issues with any of the caps or resistors being bad, but I saw test points and a chart telling me what they are supposed to read, so I made the measurements. The results are below:
TP - Measurement - (value as indicated on chart)
VA - 70V (70V)
VSC - -70V (-70V)
VS - 182V ( 175V)
Ve - 99V (165V)
Vset - 175V (173V)
Obviously the Ve is low and adjusting the variable resistor labeled Ve did nothing for my numbers. I don't know the tolerance for the VS, so that could either be good or bad. Secondly, I don't know what any of these test points are measuring. Also, both fuses that I saw tested 0 ohms. Normally when a fuse goes bad it creates an open, but I was getting a short.. so that's weird. If anybody can help me, this would be extremely awesome. Thanks.

I was able to fix the VS from being too high, but the Variable resistor for Ve has no effect on the voltages at the test point. I have found a service manual for the S42SD-YD05 through YD07 (attached), but my PDP is YB03, which I haven't been able to find online. Also, I found the schematic for the PSU (BN96-01217A), but I haven't had much success using it to troubleshoot.

I really hope someone can help me out with this.
Thanks.

[iam87x]

Re: Samsung SP-P4231 "Sparkles"

Oh and I was having a brain fart on the fuses.. they were good as well. For some reason I said fuses, but was thinking resistors. All of the fuses checked out good. So, My question is, What would cause the 60V drop in Ve? A changed value or bad resistor in the a parallel, but that doesn't explain why the Variable resistor doesn't have any effect on voltage reading.

[freakaftr8]

Re: Samsung SP-P4231 "Sparkles"

So what you're saying is the VE pot has no effect on the output voltages forve coming off the power supply and if that's the case I would consider you may have a bad optoisolator controlling that circuit along with a zener diode that goes to the VE potentiometer

[iam87x]

Re: Samsung SP-P4231 "Sparkles"

Yes. That is what I was saying. I was suggested to heat the logic and see if the display changes..but I wasn't give any specifics on where on the logic board to heat, how hot to get it and for how long. I don't have a hair dryer, but I do have a heat gun. So I know leaving it in a certain spot will eventually end up liquefying some of the solder joints. How do I go about troubleshooting the potential issues you explained or would it just be more reasonable to get a new _____ Card that those components belong to?

[ReeceyBurger123]

Re: Samsung SP-P4231 "Sparkles"

Turn Vs up by 5v should sort it.

[freakaftr8]

Re: Samsung SP-P4231 "Sparkles"

Oh and I was having a brain fart on the fuses.. they were good as well. For some reason I said fuses, but was thinking resistors. All of the fuses checked out good. So, My question is, What would cause the 60V drop in Ve? A changed value or bad resistor in the a parallel, but that doesn't explain why the Variable resistor doesn't have any effect on voltage reading.

I've worked on this power supply before and its Phillips Magnavox variant. Although I haven't run into any issues I've run into b-scan out from a shorted buffer board causing the power supply to blow and opto-isolator in the Vscan circuit along with the zener diode that goes to the potentiometer. It's very possible that you have a bad opto-isolator and zener diode combination coming off the VE pot on the power supply. If I recall this power supply goes to its minimum operating characteristics on that circuit if the optoisolator is not working. What is the number associated with that VE potentiomete? Whatever it is look for a small zener diode this would be a glass diode with a red end on one side. The optoisolator would most likely have a P number associated with the same last number of the number associated with the potentiometer.

[freakaftr8]

Re: Samsung SP-P4231 "Sparkles"

Check components PC5 and C142 to start.