Fixing My Own TV, Part II

Read Part I

Warning: This wasn't that hard of a repair, but if you don't know how to identify a capacitor or a high voltage assembly or know how to use a soldering iron, you shouldn't attempt to repair a TV set. There can be high voltages stored in capacitors and coils and in a projection set there are a lot of things to knock out of alignment or focus. Never work on a set that is plugged in and be mindful of where you are putting your hands. If possible, read the service manual for your set before beginning. That said, don't be afraid to void your warranty - particularly if it has already expired.

NOTICE: Since making this repair, I have been warned by at least two TV repair experts that I probably shouldn't have gone with the cheaper parts. There is anecdotal evidence that they have a high failure rate. I'm going with my supposition that the one that failed in my set was most likely the one that didn't have good thermal conductivity with the heat-sink, so I may be OK. Then again, they may fail this afternoon. If you are reading this and thinking of attempting it yourself, you might consider www.partstore.com as a source for the parts (or your TV manufacturer's parts site) and get the higher priced parts. Others have also suggested replacing the associated resisters connected to the convergence amps.

I think that if I hadn't been reading Make magazine and the Make blog every day, I wouldn't have attempted this. I have their t-shirt that says "If you can't open it, you don't own it", so I figured it was my duty to give it a try and I'm glad I did.

First of all, I'd like to commend www.electronix.com. Not only did they have the part for about a quarter of the price of other online parts stores, but I ordered my replacement parts on Monday with two day shipping and it was late in the day and I knew the order wouldn't ship until Tuesday. So with the holiday, I didn't expect the parts until Friday. They arrived Wednesday afternoon, so Wednesday evening, I was ready to begin. First I made a trip to Radio Shack to buy a new soldering iron and a desoldering bulb (my old iron was a bit crusty, so I bought a dual heat one with a stand since I would be working on the carpeted floor).

I disconnected everything and pushed the TV out from the wall so I could access the back. I removed about 10 hex screws and removed the fiberboard back. The inside of the set was incredibly dusty, so the first thing I did was attack it with some compressed air, trying to be careful to not blow dust onto the CRT gun lenses, the mirror, or the rear projection screen.



I found the offending components easily enough, but access was going to be a lot harder than I thought. To access the solder side of the PC board, I was going to have to disconnect about 20 wiring harness connectors.



I went and found some tape to label the jumpers with the numbers from the PC board, but when I disconnected the first one, I found the number printed on the header itself. All but about six were pre-labeled. For the six that weren't, I used a flap of tape and labeled them with a Sharpie marker.

These are the bad parts, two STK392-110 convergence amplifiers (Panasonic C5AA00000108) screwed to two large heatsinks (the Flickr picture has notes). I unscrewed them from the heat sinks and gently pried them loose with a knife blade.



Now that I had everything disconnected that I could (I didn't disconnect the high voltage wires, but I had enough slack to move the board with them connected), I unscrewed the plastic board holder from the wooden parts of the TV and tilted it 90 degrees to access the PC board.



It was pretty easy to find the solder pads for the STK392-110s, 18 pins in a row, one tilted at an odd angle. Luckily, most of the board was through-hole, but there were a smattering of surface mount components and the board was a bit flexible, so I worried that I would pop off a surface mount part. It didn't happen though. I used the soldering iron and the rubber desoldering bulb to remove the solder from the pins, then I reached behind and rocked the parts out of the holes. I had to re-heat a few of the pins to get them to release. Then I used some desoldering wick to clean up the pads.



I had read that most failures of this chip were heat related. I don't know which of the two actually failed since I was replacing both of them anyway, but I suspect it was this one that only had the heat sink grease applied to a narrow part of the chip back:



I had purchased some new heat sink compound, so I applied an even, but thin, layer on the backs of the new chips:



I then inserted the new chips into the PC board. I didn't clean the holes as well as I thought, so this was trickier than it should have been. I bent one of the pins and had to straighten it and run a piece of wire in and out of all of the holes before I tried again. Once in place, I replaced the screws holding them against the heat sinks to make sure they had good mechanical contact, then I flipped the board back up on its side and soldered each pin.

I triple checked all of my solder connections, then put the board down flat and reconnected all of the wiring harnesses, then triple checked them. When I was satisfied, I slid the board holder back in place and screwed it back to the wood.

Here are the new chips in place before I wiped off the excess heat sink compound and reconnected the wires:



One last check and a quick dusting of the lenses and mirrors, then I powered it up for a "smoke test". It worked! I screwed the back on and reconnected all of my video sources and moved it back in place. I only had to do a minor on screen convergence adjustment and then it looked perfect again.

It took me about an hour and a half. The parts cost $5.99 each, expedited shipping was around $16. New soldering iron and bulb cost me about $25 and the heat sink compound was $5. So the repair cost me less than $60 (and would have been less without tools). Compared to a repair estimate of $500, I saved over $440!

Before:


After:


Cool, huh?

Resources:

TechLore - The Consumer Electronics Community

FixYa - Technical Support, User Guides and Repair Service - this is where I got the best advice

HDTV Voice - High Definition Television Talk

www.electronix.com - Great online parts store

Service Manuals