Dixon 42" Plasma Model STY03423D (Bad picture)

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

This look like an interesting article.

Thanks for the insight! When i get a chance i will take photo's of oscilloscope waveforms for your perusal.
If this thread falls far behind how do you notice my posts. So far very few people commenting on this thread.

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Each time you post it goes back to the top of the list.


Do you have access to another logic board which would then rule it out as the problem.

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

HeLlo again, i managed to take some pictures of the underside of the Y-Sustain board where the flat ribbon enters from the logic board to show you the data comms. There are two Octal buFfer driver IC's and their output goes straight to the y buFfer board whereupon there is another octal buffer ic. The marking is 541 on the smd. It is a AHC1541.
I have also added oscillogram waveforms of two of the points coming in on the flat ribbon between the logic and Y-Sustain board. I chose the "OC1" and "LE" labelled points on the ribbon. Check out the pictures.

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

If it's an AHC1541 then use your 'scope and check the Input to Output pins. What goes in on the INPUT pins should appear on the OUTPUT pins so I would scope pins
2 --> 18,
3 --> 17,
4---> 16 etc of all the AHC1541.

The In and Out signals should be identical

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Hi again,
I added some oscilloscope wave forms for your perusal. These were taken on the data ribbon coming from the logic board going to the Y-Sustain board. These were marked as "LE" and "OC1" I don't know what they mean. I also googled the IC's and they are Octal address buffer IC's. Something like AHCT541. There are two close to the ribbon connection (I took a photo to show you) and there is another one on the Y buffer board. What if one of these chips is messing around? I really don't want to have to order a Y- Sustain and Y buffer board to sort out this problem as its going to push up the repair costs drastically.

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

sorry for the repaet but badcaps forum did not display my previous message and now suddenly it is there.

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

If it's an AHC1541 then use your 'scope and check the Input to Output pins. What goes in on the INPUT pins should appear on the OUTPUT pins so I would scope pins
2 --> 18,
3 --> 17,
4---> 16 etc of all the AHC1541.

The In and Out signals should be identical

It is such a shlep. Being that the IC's are on the underside i would have to solder a wire on a point and then screw the board back into place, hook up my scope start the tv and test. I would have to keep repeating it several times.
But if it's the only way then yea i gotta do it to prove the point.

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

I don't think those IC's are the problem. They appear to buffer the individual bits of the digital signal and if they weren't working properly then I don't think you would see anything like a picture that you currently have, even though it's only part of the overall picture.
I would think it'd either a buffer fault or an addressing problem on the logic board.

Perhaps someone can advise you as to which pins on the logic board need to be shorted in order to carry out the test pattern.

I'm out of idea's at this time.

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Thanks Dick. I dont know how to talk to others on this forum. If they don't see this thread and respond then there is nothing i can do.

[mmartell]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

What makes you think it's NOT the buffer board ? Depending on design a failed buffer IC will prevent any data being passed to the following IC in the chain giving you the symptoms you're seeing.

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Thanks mmartell. I was unsure if the data was daisy chained down the buffers. If it is then I too would be suspecting a faulty Y buffer(s)

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Thanks mmartell. I was unsure if the data was daisy chained down the buffers. If it is then I too would be suspecting a faulty Y buffer(s)

Its because manufacturers are so stingy about divulging pin out info or datasheets that we don't have a clue what is going on. Where do you get schematics of Y-SUS, X-SUS Y-Buffer ETC. Nowhere on the entire internet.
Just to put you all on the same page. When switching on the tv fom cold the entire tv is illuminated with a picture. The 4/6ths of the picture is having sparkling dots with a flutter on the picture whereas the top bit is perfect. Within 30 seconds the 4/6ths disappears and is replaced by a black screen as can be seen on the photo i uploaded.

Is there anybody out there that has a schematic of a Y-Buffer board so that i can have a look?

Regards
Angelos

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

There appears to be 3 voltage regulators on your logic board. Possibly 3.3V, 2.5V and 1.8V
Are those voltage there.
Is there also a led and does the flash sequence change when when you lose the large part of the picture on screen

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Kudo's goes to Mmartell who said that the buffer IC's are daisy chained. The problem being that the customer had not brought in the footpiece and i could not do proper fault diagnosing. Today with the TV on its footpiece i went straight to the third buffer IC from the top and sprayed it with cold spray when the symptom started. It solved the issue temporarily. So i now know its either the chip or dry joint on IC. I removed that mucky silicon and will try to reflow the IC to see what happens.
Just another question. What kind of silicon (or whatever it is) can i use to reapply this sealant, I assume its job is to avoid dust from settling between the legs thus causing an arc flash?

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Update: after reflowing the chip the problem is sorted out. Thanks to all for their input....

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

Glad you got it sorted out. How did you do the reflow?

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

I used a paint stripper gun heating it from the bottom whilst monitoring the surface temperature. I still want to buy a oven specific to SMT reflowing but they are quite expensive.
Tell me. What do you use to reseal the Y-buffer chip? I took off some soft stuff like silicon. Not sure.

[dick_barton]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

I've never successfully replaced any of those chips but I would imagine you would be looking for a flexible electrical silicon type sealant.

I know others on this site have replaced these IC's so it would be worth doing a search to see what further information you can find.

[mmartell]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

I used hot glue. Probably not the best but you're right about primarily keeping junk out that would short the high voltages on those pins.

[angelos]

Re: Dixon 42" Plasma Model STY03423D (Bad picture)

I used all purpose silicon. because i was paranoid. i squeezed some silicon out on the table and shoved my fluke probes into it and got infinity so.... all's well. Lets hope my fix lasts.
Thanks once again.