50" Samsung Plasma (model number PS50Q91HD) - possible purchase

[tom66]

Originally Posted by psmedley

Shame there are no pin layouts to truly show what is power and earth to enable more accurate testing...

Sounds like your upper buffer has had it, sadly. But you should be okay with testing with just the lower buffer for now.

The power and ground are fairly obvious; look carefully at how the PCB connects to the pins, you can see the break on the upper pins.

[psmedley]

OK I'll go ahead and order the ysus repair kit. Once installed, I'll test with the upper buffer removed to avoid blowing the repaired ysus. Presumably I'll only get half a picture?

If it's working, I'll then go find the upper buffer board.

Thanks again for all your help and patience

[tom66]

Originally Posted by psmedley

OK I'll go ahead and order the ysus repair kit. Once installed, I'll test with the upper buffer removed to avoid blowing the repaired ysus. Presumably I'll only get half a picture?

If it's working, I'll then go find the upper buffer board.

Thanks again for all your help and patience

Yep, you will have a missing half of the screen but it should be good for testing.

Note a common failure on these buffer boards is those ceramic caps, at least on Hitachi plasmas (when they used to actually make PDPs.) Since you've got a high-resistance short of 5 ohms you might be able to narrow it down with a meter; or you could get a power supply capable of a couple of amps and run that through it, and see if anything smokes.

[scokljat]

Originally Posted by psmedley

Photos of buffers attached.

The connectors look pretty similar to the Coppell photos...

Once you make it work, it could be good idea to put small heatsink on each buffer chip. There are some cheap 9x9x5mm little heatsinks on ebay just to fit in the middle on buffer IC top, not touching protective glue on IC terminals.

There is also youtube video, a guy replacing a buffer IC. Maybe if you find one or two of your chips shorted, just replace them for same good chips from other nonfunctional Y-buffer board. I believe you can get nonfunctional Y buffer board for free or very cheap and salvage few working IC's from it. I know it's a lot of work, but can save you the money, especially in this point when you already invested too much...

Take a look, this looks similar to your board:

Part1:
http://www.youtube.com/watch?v=5hVi5gd0aec
Part2:
http://www.youtube.com/watch?v=GkZ7Y...feature=relmfu
Part3:
http://www.youtube.com/watch?v=KjNU4...feature=relmfu

Wish you luck!

Cheers!

Suad

Edit: there are also cheap brand new scan IC's for your buffer board on ebay: 1pcs 2.20$, 10psc 19$ free shipping. Btw, is it allowed to post links to ebay on this forum?

[psmedley]

LOL I think I found the problem with the upper buffer board... I didn't notice it earlier, but note the top buffer chip on the upper buffer board...

I've attached a closeup for clarity,and also of the reverse of the board.

Do you think that *might* be the short???!!??

...and of course, now I look back, I see that it was damaged way back in http://www.badcaps.net/forum/attachm...1&d=1339659556 too

[tom66]

It's normal for ICs to melt in operation don't you know? Remember to keep the magic smoke, you can probably fit it back in. Anyway you could cut the epoxy off the chip and hot air it off, then run the TV without that IC. You will get a black bar.

I almost wonder if this is where the failure originated. A shorted buffer loading down the power supply a lot, and the user running it for a while trying to get it working, then eventually killing the PSU MOSFETs.

Though the bottom is probably just flux... I imagine a lot of them will look like that.

Generally I perform a visual inspection of all boards when I get a set, but that is fairly subtle as it looks like just a mark on the IC from a distance.

[psmedley]

Well ysus is fed Vs, and the shorted mosfets are from the Vs tract so that sounds logical...

I (of course) don't have a hot air gun - any other way to remove these chips?

[tom66]

Originally Posted by psmedley

I (of course) don't have a hot air gun - any other way to remove these chips?

Paint stripper gun works well. Used one at work as all the hot air stations were nicked by the production staff!

[psmedley]

Don't have a paint stripper either :P

Something like http://www.ebay.com.au/itm/270929815980 should do the trick. It will probably help remove the surface mounted mosfet that's blown on the ysus too

[tom66]

Originally Posted by psmedley

Don't have a paint stripper either :P

Something like http://www.ebay.com.au/itm/270929815980 should do the trick. It will probably help remove the surface mounted mosfet that's blown on the ysus too

How much are you going to spend on this TV, another AU$52? I can get a cheap paint stripper here for £20.

[psmedley]

Well I figure a hot air gun will come in useful for other things.... 20 quid is $A31 anyway....

I don't mind spending money on tools that I can use for more than one job...

[psmedley]

Found a cheaper hot air gun closer to home - http://www.ebay.com.au/itm/320762390919

Got the mosfets removed from the ysus board this evening - except for the surface mount one - I'll wait for the hot air gun to try and remove that from the pcb.

Turns out the K2837 and one of the 88N30's are shorted (and of course the blown 20NK50) - the other 3x 88N30's appear OK out of circuit, however I'll replace them anyway.

[scokljat]

Originally Posted by psmedley

Well ysus is fed Vs, and the shorted mosfets are from the Vs tract so that sounds logical...

I (of course) don't have a hot air gun - any other way to remove these chips?

Hot air gun is the best way, but it's possible to do it without it. What I would do is to remove the glue/epoxy and carefully cut all IC legs with fine small scissors or nail pliers or carefully cut them with scalpel NOT touching and destroying pcb. Once you have all legs cut, apply some solder underneath on center pin, heat it with solder iron and IC will eventually just come off. Apply some solder and flux, pick up all IC legs with solder (they will just come off when heated and stay on soldering iron top) and clean all concatcs as well as large center pin (used for cooling). Solder wick comes very handy. Before testing without IC, inspect carefully that you cleaned all solder and there are no shorts.
If you get picture with black bar on top, that's great. When you get to the point to solder new chip on, don't forget to apply lot of solder underneath on center pin enough to solder pass through holes and connect IC center. A guy from youtube actually forgot that ;-)

There are very cheap scan IC's on ebay:
http://www.ebay.com/itm/1PCS-IC-FE34...#ht_1978wt_946

Hope this helps,

Cheers!

Suad

[scokljat]

Any progress here??

[psmedley]

No - ysus repair kit ordered from the UK - but not expected until sometime next week.

My hot air gun arrived yesterday, so I'll remove the buffer chip from the upper y buffer and confirm that that eliminates the short when I get an opportunity.

Other than that, it's a waiting game

[scokljat]

Originally Posted by psmedley

No - ysus repair kit ordered from the UK - but not expected until sometime next week.

My hot air gun arrived yesterday, so I'll remove the buffer chip from the upper y buffer and confirm that that eliminates the short when I get an opportunity.

Other than that, it's a waiting game

When you install new YSUS FET's maybe you should try without whole upper y buffer board. Topmost IC on upper buffer board is visibly blown and should be replaced, but maybe there are more shorted IC's on the same board but not visibly blown. Even if you remove topmost IC other possibly shorted IC's can blow Y FET's again. Testing with new FET's and lower buffer only (which you confirmed has no shorts) would ideally produce normal picture on the lower half of the screen. If that happens, you can start celebrating ;-)

Cheers!

Suad

[psmedley]

Well I was going to do initial power up with repaired ysus with NO buffer boards connected

Then I'll try lower buffer... I'll also retest upper board for shorts once blown 3407F chip is removed to confirm no shorts...

[psmedley]

Ysus repair kit arrived today (6 days from UK - impressive). 3 pin mosfets installed ready to solder, still need to install the surface mount mosfet and work out how best to solder the base to the PCB.

Also need to test the resistors that are included in the repair kit R5508, R5509 and zener diode ZD5502 - although the zener appears visually to be ok.

The included 680uf 25v caps were Jackcon - they'll be going straight in the bin Already replaced them with Rubycons Will try finish off the repairs tomorrow evening.

[tom66]

Originally Posted by psmedley

The included 680uf 25v caps were Jackcon - they'll be going straight in the bin Already replaced them with Rubycons Will try finish off the repairs tomorrow evening.

Keep the Jackcons - they make good firecrackers.

[tom66]

For the tab/tag pin of the FET, use solder paste and a soldering iron, or flow solder under it while pressing it down. (Solder the other two pins first.)