Samsung Ps42b451 no picture losing vs voltage

[Azza111111]

Hi guys,

Got myself a Samsung ps42b451 going cheap,

Has no picture but has sound, to be honest a replacement ysus was cheap at £15 so I tried replacing it to no avail.

I removed the buffer board and checked all its ic's for shorts with a dmm. It checks out fine and all ic look undamaged.

However when I check for vs voltage with the buffer board attached I have no voltage, when I remove the buffer board I have full vs voltage again.

Could the buffer board still be bringing the set down even if it appears to have no shorts?

I was thinking of getting another buffer but that's another £20 and if that doesn't work a cheap tv starts to get expensive Lol.

One other thing I've noticed a couple on times when turning the tv on is a quick flash of part of the screen lighting up, I've only seen this twice in about 20 times turning on though.

Tv has sound and responds to button presses and remote.

Any help would be greatly appreciated.

[freakaftr8]

Re: Samsung Ps42b451 no picture losing vs voltage

Yes I would say most likely still a bad buffer board. I have found in some cases very rare but they don't test shorted however the reading might be down and K ohms instead of M ohms. Shorted is still shorted replace it. The reason you see partial screen lighting up is because the protection circuit hasn't kicked in fully by the time screen tries to light.

What is the average reading across all pins?

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

Yes I would say most likely still a bad buffer board. I have found in some cases very rare but they don't test shorted however the reading might be down and K ohms instead of M ohms. Shorted is still shorted replace it. The reason you see partial screen lighting up is because the protection circuit hasn't kicked in fully by the time screen tries to light.

What is the average reading across all pins?

Thanks for the information that's great, I will check again with a meter and post the results. Happy to get another buffer if there's half a chance I'll fix it 😮but will test again first...

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

The average readings were .700 m ohms to ground across that whole board +/- .10 m ohms...

[freakaftr8]

Re: Samsung Ps42b451 no picture losing vs voltage

What happens if zsus is disconnected and ysus buffer installed?

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

What happens if zsus is disconnected and ysus buffer installed?

Unfortunately the tv still doesnot light up with zsus disconnected.

Do you think the buffer readings look ok? Cheers

[freakaftr8]

Re: Samsung Ps42b451 no picture losing vs voltage

Well the buffer board reading sound about right you don't have a couple pins that short to ground? All readings across all pins are .700 or so megohms?

Also there probably will not be a picture however are you sustaining proper voltages with the zsus disconnected? And is this the model that the ysus carries the power from the power supply and the zsus gets the power from the ysus? If so the power supply may not come up and stay on with one sustain board disconnected.

Interesting how the vs stays up while the buffer board is disconnect. This only leads to a short in the buffer

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

Well the buffer board reading sound about right you don't have a couple pins that short to ground? All readings across all pins are .700 or so megohms?

Also there probably will not be a picture however are you sustaining proper voltages with the zsus disconnected? And is this the model that the ysus carries the power from the power supply and the zsus gets the power from the ysus? If so the power supply may not come up and stay on with one sustain board disconnected.

Interesting how the vs stays up while the buffer board is disconnect. This only leads to a short in the buffer

OK I've done some more testing, disconnected zsus still gives me the same voltage drop on vs.

I think my information may have been a little poor as I've realised that I have the 207v with ysus disconnected but I lose it as soon as I reconnect the ysus.

Definitely no shorted pins on the buffer by the way...

So maybe I've been sent a faulty ysus? Or something is killing them?

Sorry for the misleading info.

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

OK now I'm confused, with the ysus disconnected I had a steady 207v.

I then reconnected and tested and lost the 207v.

I disconnect ysus again and the 207very is gone.

So with ysus and buffer out I have no 207 heading that was but have the 207 to the zsus.

Maybe intermittent psu???

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

Checked the power board, all caps look and test ok and I re soldered any cracked joints/iffy look joints. Still no different.

[freakaftr8]

Re: Samsung Ps42b451 no picture losing vs voltage

Interesting. I wonder if the ysus is bad and now destroyed power supply, do you still have 5 volts on standby pins

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

Interesting. I wonder if the ysus is bad and now destroyed power supply, do you still have 5 volts on standby pins

Yeah I still have my 5v standby and power on.

Weirdly I've now got the 207 volts back with buffer disconnected, for some reason it's lost for a minute or so after the buffer is plugged in.

I think I should replace the buffer board, it pains me to do so as it meters out ok but what else could it be?

Really appreciate the help you've given by the way.

[freakaftr8]

Re: Samsung Ps42b451 no picture losing vs voltage

It's gotta be the buffer board.

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

It's gotta be the buffer board.

I think so
Thanks for you help dude. I will post back once done.

[Azza111111]

Re: Samsung Ps42b451 no picture losing vs voltage

It's gotta be the buffer board.

I thought I'd post back, got the tv working. It was all a bit weird, I purchased another buffer board and fitted it. It still didn't work.

I then put back in the original ysus ( that I replaced a small capacitor on which looked ok but tested bad) and the set fired up and worked great.

I think both ysus and buffer were faulty but I will take a look at the spare ysus as faulty from an eBay seller which is odd.

Thanks for all your help, made a nice tv for cheap. Thanks again.

Aaron