Another Samsung HP-T5064, Good Sound, No Picture

[johnboy1313]

I picked this set up this afternoon. The set powers on and off with the power button on the front. The audio works. Vol+ and Vol- work. No picture.

Vs = 207V
Va = 63V

I don't know where to measure Vsc and Ve.

I have 5.3V and 12V at the appropriate pins on the PSU. I see no bulged caps. With that said, the training manual (Thanks Tom) asks if Vs and Va are normal with CN810, CN809, CN808, and CN807 disconnected. If "No", then change power supply.

In my case, Vs = 34V with those plugs disconnected, but CN807 contains Vs_on, so I'd honestly be surprised to see a normal Vs with this plug disconnected.

The fuse on Ysus is good, as is the fuse on Xsus. I see 207V at both ends of each fuse. Both heat sinks on X get warm. It seems like neither heat sink on Y gets warm.

I see no obviously blown ICs on the buffers.
The screen does not prime, nor does it buzz as it might if cracked.

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

Depending on the design, VSON may be active low or high.

Apply self-test as indicated here:
https://www.badcaps.net/forum/showthread.php?t=26790

Disconnect Y-main/X-main too, then check Vs and Va, with self-test applied.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

I'll have to find a remote control to access the service menu

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

That's not necessary for a Samsung..

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

Cool. I'm away from the set right now. I'll check it out when I get home.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

I'm looking at boards on shopjimmy. It looks like they all (or most anyway) have a six pin connector block not a four pin. Do I short pins 5-6 instead of 3-4?

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

So, I'm not really sure what I was trying to see with the self test. I jumpered 5-6 as in the picture below. With everything connected but the LVDS cable, there was no panel prime or test pattern like I was expecting, though my expectations could be wrong. With Y and X disconnected, Vs =207V; Va=63V.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

At this point, I'm still not sure where to focus my attention. The fact that the heatsinks on the Y-SUS are still cold points me in that direction. I'm going to get the scope from work today but I'll need to know where the test points are.

From reading on the net it looks like a bad buffer on these sets will wipe out the Y-sus. Once I have the scope, is testing the buffers on a Samsung anything like testing the buffers on an LG panel?

I see many repair kits for the Y-SUS offered on eBay that consist of several mosfets, some resistors, some caps, and a diode. Seems like I can fix this one myself, so that's kinda cool. Anyone here got any tips?

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

Can I see an overall shot of your control board?
The self test is an attempt to get VS and VA to come up with the Y-main and X-main connected.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

Can I see an overall shot of your control board?
The self test is an attempt to get VS and VA to come up with the Y-main and X-main connected.

Vs and Va were both normal with everything connected, even without doing the self test. This is my board, though the pic is stolen from shopjimmy.

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

In which case, use your scope to check the Y-main and X-main waveforms.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

I forgot to grab the scope. I'll get it on Monday.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

I watched your video on testing the buffers, Tom. Both buffers test good. I've got the Y-sus sitting here on the table in front of me. I've been reading about repairing the Y-sus.

https://www.badcaps.net/forum/showth...ung+plasma+fet

Should I just start pulling and testing the FETs one by one, or wait til I have the scope and see what the output from the Y-sus looks like?

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

I'd wait for the scope, but if you're bored in the meantime, look up the datasheet of each of the MOSFETs/IGBTs on the heatsinks and test drain-source on each.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

In or out of circuit?

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

In circuit is fine, but once you locate a suspect device remove it and test out of circuit.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

Ok

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

There are two K2837's on the board. They both measure different. I'm not sure which one to suspect. (+ and - symbols represent leads from the DMM)

Q5200
Toshiba K2837
+Gate to -Drain = 6.5Mohms
-Gate to +Drain = O.L
+Drain to -Source = O.L
-Drain to +Source = 6.25Mohms
+Gate to -Source = 9.98kohms
-Gate to +Source = 9.98kohms

Q55000
Toshiba K2837
+Gate to -Drain = 0.890Mohms
-Gate to +Drain = 14.77Mohms
+Drain to -Source = 14.85Mohms
-Drain to +Source = 0.867Mohms
+Gate to -Source = 9.96kohms
-Gate to +Source = 9.86kohms

[tom66]

Re: Another Samsung HP-T5064, Good Sound, No Picture

They look OK to me. Remember, 99.9% of the time, a FET/IGBT fails shorted.

[johnboy1313]

Re: Another Samsung HP-T5064, Good Sound, No Picture

So it's ok that they have such different readings?