Samsung 50" Plasma HPT5044 No Picture

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

There's little sense in checking fuses with power on, except low voltage DC ones.

[DavidOH]

Re: Samsung 50" Plasma HPT5044 No Picture

Maybe I didn't ask that right. I was just wondering what the volts should be at the middle fuse holder. I was just trying to narrow down where the problem might be. What you posted before will help when I get time to spend on it. When your work day is 12/14hrs. long it doesn't leave much time for anything esle.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

You need a reference to test against. If the fuse is on the isolated sides (for example, the sustain boards) then you can test with black probe on chassis. If it is on the primary, you test either relative to neutral or the negative lead of the big 400V caps on PSU.

[chuckup]

Re: Samsung 50" Plasma HPT5044 No Picture

Hello All,

I have this exact model with the exact symptoms. I found a few fets that were shorted on both the bottom and top heat sinks. I replaced all the fets on both heat sinks Q5100-Q5103, Q5200, Q5500, Q5302-Q5304 and the surface mounted fet Q5501. I checked all other components surrounding the above mentioned fets and didn't find any failures.

Fuse 5702 on the Y-Main was blown and was replaced. Two upper buffer board IC's blown. Lower buffer board checked out ok with DMM. Removed and replaced both failed buffer IC's. Upper buffer now checks ok with DMM.

Recapped secondary side of PSU. Powered on with just the PSU first. VA and VS good, 207 and 63. Attached all cabling. During startup fullscreen just flickers once and goes off. After a couple of attempts with same results an IC on the lower buffer blew. Expected this might happen since the recommendation is to change all three boards.

I am attaching some o-scope pictures for the pros to look at to see if my Y-Main is working properly. Hope to just purchase a set of buffer boards. These are without both buffer boards in the TV. FYI, The heat sink for the lower buffer board remains cold. Also a picture of the the X-Main out.

Thanks all!

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Those waves look good.

[chuckup]

Re: Samsung 50" Plasma HPT5044 No Picture

Thanks Tom!

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Nice Agilent scope, btw. You make me jealous...

Only comment I would make, it looks like you have no SETUP wave. This would cause a very poor picture. Often on these sets the Toshiba FET gets taken out at the same time as the other four, please check it too. K2837 I think.

[chuckup]

Re: Samsung 50" Plasma HPT5044 No Picture

Tom,

I actually changed them both. Only one was failed. The failed one was grouped with the upper heat sink fets part# RJH3047. Only one of these fets were shorted but changed them all. The lower heat sink had two 88N30W fets and B20NK50K shorted. Changed all of them. The lower heat sink stays cold to the touch. I am wondering if there still may be an issue with the Y-Main.

The scope is my baby...goes everywhere with me!

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

I have a Rigol DS1102E... does the job, was cheap. Though I am planning to upgrade to a DS2072 (if they fix the bugs) or maybe a 2000X (if I think it's worth it.) I get to use very similar scopes in the uni labs.

Right now I can't see it damaging the buffer, but I think you will get a very poor picture on the display. Have you tried adjusting Yfr?

[chuckup]

Re: Samsung 50" Plasma HPT5044 No Picture

I have seen your scope. I watched your youtube video where you were setting the trigger for the Y-Sustain. Thanks again...I have not tried adjusting the YFr yet. I have ordered a set of buffers and should arrive some time late next week. In the meantime I am going to do some more continuity checking. The Vscan is supposed to be -180. I am seeing -4.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Low Vscan indicates there are still problems on the Y-sus. You should be seeing the reset waveform extending below the ground level. I think it may actually go to Vscan (negative); though I can't remember if that's the case on a Samsung plasma. This may explain why the reset waveform looks very poor. I do not expect a good image.

[skidmark]

Re: Samsung 50" Plasma HPT5044 No Picture

I was just given a Samsung HPT5054 with same problem also. No surprise huh. Anyway I'm 90% sure that at least most of the problem is on the main scan drive board. I've checked most of the MOSFETS on the board and several of them show a dead short. I'm waiting on a larger tip for my desoldering gun to arrive so I can get busy.
Has anyone ever replaced the MOSFETS on any of the boards in this TV. It looks like you almost have to unsolder every FET on some of the heatsinks just to replace one.
One final question, does anyone have a list of all the FET and big transistor part numbers?

[skidmark]

Re: Samsung 50" Plasma HPT5044 No Picture

oops forgot the photo

Is that standalone Toshiba the same FET or an odd ball in the bunch?

[skidmark]

Re: Samsung 50" Plasma HPT5044 No Picture

Does anyone know of a single source for all the FETS, transistors, etc in the Samsung driver boards.
88N30
K2837
RJP3043
RJH3047
STTH20P03S

Thanks Al

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Try shopjimmy they have a kit for this ysus which may have all those components.

[tw2005]

Re: Samsung 50" Plasma HPT5044 No Picture

keep in mind the Ymain is most likely only part of the problem. real chance the upper buffer board is also short, that's the general way these go.

I'd be checking that first before fixing the ymain as you're going to either be able to replace the buffer ICs or find a working board which may be challenging and not cheap.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I'm working on another one of these myself and blew up a couple of scan ic's by moving a little too fast. I suspect something wrong with the ysus (or just paranoid). How do these forms look ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Looks pretty poor, what's V/div setting?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

50mV 5x magnification 10x probe

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Yeah, that's a dead sus output there, no activity at all, you're seeing gate coupling from the transistors. Do you have Vs present?

Here's some waveforms from a Panasonic G10, 2009 FHD panel, so going to be a little different, but should give you an idea, all waves 100V/div with GND at centre.

1. Y drive: Single frame showing a total of 12 subfields, one reset ramp at beginning of frame
3. Y and Z/X drive: Reset ramp from both sides of panel, showing Ve bias and Vset/-Vad ramps
4. Y and Z/X drive: Detail of one subfield showing alternate sustain drive pulses and reset pulse at end of field
2. Z/X drive: Single frame showing 12 subfields, reset in middle of frame