Saturday, October 5, 2013

Repairing a 42" Plasma LG TV


A couple days after the end of 2.00 Gokart there was a huge supply of electric vehicle goodies. Unfortunately, I was at the final performance of Roadkill Buffet, "MIT's premier improv comedy troupe", while most of the good cruft got crufted. Some of the earlier crufters got their hands on a 42" plasma LG TV and tried fixing it on the spot (thinking it was just a blown fuse). By the time I got there, they were giving up on it. So, being the naive and ambitious person I am, I decided to carry it back to EC and learn a bit about how plasma televisions work. Thankfully Ed Moriarty was there cleaning out the 2.007 Underwater Vehicle section's materials, and was able to drive the TV over to East Campus. After some debugging and replacing some parts, I ended up with a pretty big monitor. 

Keep in mind, this all happened a couple months ago. I'm spending a whole day blogging in an effort to catch up and keep a consistent post rate.


SYMPTOMS:

Blown fuse (FS152) on the Y-Sustain (Y-SUS) board near the power supply connection.
Bulging Capacitors 250WV 330uF (C154 and C153).
Screen doesn't respond to anything.
Power switch LED turns on followed by a quiet relay click.

Since the previous crufters tried switching the blown fuses to no avail, I thought maybe the capacitors were the problem. I spent a good portion of a day going through all the cruft sites at MIT looking for power supplies. 


I eventually found a capacitor that was rated for 250WV and over 330uF. Bailey and the internet said that capacitors with the same working voltage and higher capacitance would work. 


Old bulging capacitors.





After replacing the capacitors, I tried testing the screen again.

 

To test the screen and whether or not the sound worked, I hooked up W5's GameCube with Super Smash Bros running. The TV has great speakers; it's just the video that's dead. 

Internet! I'm suspecting either a problem the power supply supplying to much current, or a faulty component on the Y-Sustain board causing a surge from the power supply.


A quick Google search for "YSUS 6871QYH051P FS152" resulted in a great blog post for troubleshooting bad IPMs (Intelligent Power Modules). The Coppell TV repair online blog tested Sanyo's STK795-518 (which is the IPM used in Y-SUS board LJ92-01200A), but it also works for many Y-SUS IPMs.



One easy way to fix the board would be to buy a new one. However, because it's faster it costs more; most sites list $100+ (not including shipping) for a functioning Y-SUS board. There's a programmer's saying "good, fast, cheap: pick any two". If soldering isn't your thing and you don't mind paying for it, this is probably the safest/fastest way to repair your television.

Another cheaper alternative to repairing the board is to buy the specific components that are dead. Most of the board is still good (or so I thought). I bought a new IPM and the proper capacitors for a total repair cost of $37.50

Shipping...

I replaced the fuses with 4A 250V fuse from CSAIL and checked them to make sure they wouldn't blow before I put the nice IPM on the Y-SUS board.

New IPM :D

Once the new IPM came, I did the same continuity check to ensure that the old IPM was definitely a problem.



It checked out! Time to anti-solder.


I used MITER's big soldering iron, because the little iron I had didn't put out enough heat. 





Rubbing alcohol is great at removing the old thermal paste from the heat sink. I replaced the old paste with some Arctic Silver high-denisty polysynthetic silver using an old USTA Membership card.



While soldering the new IPM on, I also switched out the temporary 250WV 470uF capacitors with 250WV 330uF. I didn't want to risk the different capacitors messing up the new (most expensive part of this project) IPM. I don't want to wait another week.

Sooo...

It turns out that the IPM wasn't the only problem. When I replaced it, the screen started warming up like it was just about to flicker on... then blue sparks and smoke. These sparks happened in a location with tiny surface mounted components. After further research, I decided investing in a one-hundred dollar Y-Sustain board would fix the problem with a high degree of certainty. 

Shipping...

While waiting for the new Y-SUS board to come in, I built a mount modification to fit my dorm room bed. 


The mount that came with the television had a hole arrangement that fit the 2 x 4 bed frame loft.  


I found some 5/8" x 4" aluminum stock at MITERS that I could side tap to bolt to the tv mount.



I clamped them together (in opposite orientations) and drilled holes that were offset from the center axis by 1/2". When I finished, I flipped one over so the hole pattern was mirrored. This would prevent the screws from colliding when attaching it to the loft.  


I drilled and tapped side holes for 4" 7/16 bolts. 


And countersunk the holes for the wood screws to set into. 




Assembled and attached to the bed frame. Now all that's left is plugging in the new Y-SUS board when it arrives and hope that it fixes the dead screen problem. 

"[Fred Desk] Package at East Campus Desk [2013-07-18]"


Old Y-SUS
New Y-SUS
Before I plugged the new board in, I did a few more tests with the multimeter. I hadn't ruled out the possibility that the Power Supply board wasn't the cause of the blown fuse. It could have either been the IPM failing and drawing too much current or the Power Supply surging and pushing too much through the fuse causing the IPM to short somewhere. After checking the output voltages from the Power Supply and determining them safe, I plugged in the new board and tested it. 

I've never been happier to see static!




Mounted and working LG TV
I finished screwing in the back panel, and mounted to my bed. All setup and ready for Suits.



After having a ton of fun watching too much TV and catching up on too many shows, summer time came to an end. I moved back onto Fifth West, which meant carrying it up four flights of stairs.



Raku, my room-mate freshman year, moved to ADPhi, and left me with a single. I decided to keep the other bed for guests which has been quite useful. Also, the board spanning the two lofts is a perfect space for a giant TV. 

 

In addition to the TV, I made a huge whiteboard desk for working out psets and sketching up ideas while building. Ever since FIRST and FTC, I've placed an emphasis on documenting my sketches. In order to preserve all the sketches and design doodles that happen on the whiteboard, I'm making a time-lapse set up with a Raspberry Pi and Pi Cam. 


The TV replaced the pull-up bar - brings a whole new meaning to "couch potato".

1 comment:

  1. had an great experience with this Plasma TV and fabulous Picture Quality

    ReplyDelete