Samsung HP-R5052 snow at top and bottom of screen (pics)

[2dbit]

I have got a plasma that blew out it's power supply. I replaced the power supply with one from fleabay, and was happy to see that the tv now turned on, but has image issues at the top and bottom of the screen. Here's some pics:







All output voltages are set to match the TV's sticker, using a DVM they're all reading within 0.2v.

I attempted to mess with settings like the timing, but doing so only made the picture worse, and resulted in additional snow...what is being seen in the pictures is actually the best it can be(timing wise)

I hooked up my oscilloscope to the VS and VA outputs, and this is what I've got. (this is back probing the connectors while all still attached and powering the TV)





Any thoughts?

[freakaftr8]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Looks like a ysus issue. I see a lot of static in the voltages on the oscilloscope. Try disconnecting ysus from power supply and check waveform. Also with a dmm what's the vs and va look like. Fluttering voltage or stable?

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Went ahead and pulled the connector off the Y-Sus board. I took readings with the same scaling and at the same point as before. here's the result...

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

When checked with a DVM, both were rock solid. I was surprised to see that much noise, especially on the 200v rail. would have expected to at least flip around 0.1v or so!

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

With that kind of image, you're pulling more than rated current, so it's not entirely surprising the power supply is struggling.

The fault is probably with Vset/-Vsc circuits, or the timing - we've had a failed transistor cause this on a Y-main before.

To test, you need to sync your scope to 60Hz mains and feed in 60 Hz signal, or find a way of using EXT TRIG to sync it to the video. Then probe Y-main output.

Also, check Ve with a multimeter, make sure it is not too high.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Ok, I have the option to sync the trigger to the AC line. I could also use the Ext trigger, but would need some guidance on how you want that setup. I have a signal generator (so to speak) on my phone that does produce a nice clean signal. I could feed that in wherever necessary.

Here's a pic of the board. If you could help with where I need to be probing, I would appreciate it!

[freakaftr8]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Check those MOSFET transistors on that aluminum rail
Left side on pic 1

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Check here - scope probe on red, ground lead on black.
Make sure to use 10X probe.

Output can ramp up to 400V.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Check here - scope probe on red, ground lead on black.
Make sure to use 10X probe.

Output can ramp up to 400V.

Not sure if you meant to attach a picture or not...

My scope has a 10x probe, but the input is only rated to 400v. I doubt the scope destructs at that 400v mark, but I am mildly concerned about a defect causing the voltage to surpass that.

My DVM can take up to 1K. Is this something I can check first with my DVM and then when confirmed to be within the 400v limit of the scope, then connect the scope to see the trace?

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

The Vset ramp is typically 2 x Vs, peak voltage depends on the Vs rating, but is in the range of 360 to 420V for a couple of µs about 60 times a second. This transient is unlikely to cause harm. The rating on your 10X probe should be observed. The oscilloscope will only see approximately 1/10th that so should be protected.

Check the datasheet of your oscilloscope to see what the input specifications are. Mine is rated to ±1kV transient for 8/20us load dump. The set up ramp fits within this limit, even though it is not a load dump.

I have used a Rigol DS1102E to measure sustain waveform fine, but I used a 600V rated fixed 10X probe. Most manufacturers only supply 300V rated probes with their instruments.

And, d'oh, here's picture...:

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

I was unable to locate any data regarding the input transient allowance. Only the 400v rating.

Suppose it would be true that the input can be up to 400v, but if I have the probe set to 10x, then only 200v would actually be reaching the scope....

Surprisingly, the probes supplied are 600v probes...wouldn't have seen that coming from a cheap(er) unit... (It's an Atten 1062CAL)

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Should be fine. Your scope will see 60V max from a 600V input but probe MUST be on 10X setting for this to be valid. A bit of tape to hold switch would be ideal. 10X divides input by 10.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Ok, I went ahead and scoped it...it's all over the place frequency wise... Here's a few screen shots to at least get the picture...

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

The SET DN ramp looks too long to me. Try adjusting Yrr control.
First screenshot, 500us ramp is too long. Should be about 150 to 200us from my experience.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

When I had it running, the image was flying back and forth very fast, the signal was very sporadic. The voltage was always about the same, but the frequency would jump all over the place. Anywhere from what is seen in the first pic, to the third pic.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Check those MOSFET transistors on that aluminum rail
Left side on pic 1

If one of those Fets was toast, wouldn't it pull to the point of popping a fuse?

[tom66]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

When I had it running, the image was flying back and forth very fast, the signal was very sporadic. The voltage was always about the same, but the frequency would jump all over the place. Anywhere from what is seen in the first pic, to the third pic.

Yes, you need to sync to incoming video then. You can do that by e.g. using a split composite video cable and tying your scope channel 2 to a video trigger (most DSOs have video triggers.)

If one of those Fets was toast, wouldn't it pull to the point of popping a fuse?

Not necessarily, can affect the sub-voltages on the transformer which aren't fused. Also, they can simply become leaky and cause a variety of issues.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

I currently do not have a Y splitter for composite, so I'll have to go pick one of those up prior to testing. I did some reading on my oscilloscope and found it has a whole section dedicated to syncing to a TV signal. Of course a lot of it comes across as jargon without the unit in operation to see what each of the settings is really doing.

Back to the YRR adjustment. I have played with that doing a visual check as I adjust it. Adjustment of that potentiometer in either direction made the image worse. Whatever is going on here is more than just poor adjustment...

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Ok, I'm sure I'm still doing something not quite right. I wasn't able to get the trace to hold still on the screen. However, if I stopped the oscilloscope, I was able to scroll left to right and see essentially a signal that would build, collapse, and start over. Not sure if this is what I want to see, or if I'm still not setting it up quite right.

Here's a two screen shots, the second is when I scrolled off to the right to continue from the first...





I took what was being seen and zoomed in to see a better detail, here's that screen shot.

[2dbit]

Re: Samsung HP-R5052 snow at top and bottom of screen (pics)

Is this the sort of signal that should be seen at this point?