Saturday, November 28, 2009

TV repair tools: screwdriver, wrench, drill...Did you say "drill"?

A few weeks back my Samsung DLP TV went on the fritz; showing a green tile pattern when playing analog sources, and randomly freezing when playing HDMI sources. After doing some research I found that this is known problem in the digital board on the HLR5067WAX/XAA and other TVs in the series where the DNIe chip (which is a BGA-type package) develops a loose connection. (Root cause was probably a mistake in the solder mask or poor QC on application of the solder paste prior to chip placement.)

The problem can be resolved by (of course) purchasing a new digital board for hundreds of dollars. Some of the sharp minds in the peer forums over at Home Theater Shack have found that if you can apply pressure to the DNIe chip, the problem goes away. So I opted to follow the process outlined by Leonard and Tito over at HTS for installing a mechanical pressure arm to push on the DNIe chip. I figured it was a few bucks, a trip to the hardware store, and some of my time.

I built the arm into the digital board's RFI/EMI cover, adjusted it to apply just a bit of pressure, and re-assembled the TV. Works 100%. Saved myself a few hundred dollars and now I can say I once fixed a TV with a drill and a tube of Loctite.

Sunday, November 22, 2009

SO2R -- The hard way

This past weekend I had the privilege to be a guest operator for the Radio Club of America on their special event station W2RCA, celebrating the 100th anniversary of the RCA. The station was co-located with the anniversary event in Washington DC, and I wasn't able to attend in person, so the operation was handled using remote PC access and VOIP software, similar to the setup which I described back in late 2007.

A problem with remote setups is that they require a fast Internet connection to work well; the primary challenge being the speed (or lack thereof) at which you can switch from receive to transmit and back again. Because the W2RCA special event station was scheduled to happen during the ARRL's November SSB Sweepstakes, it was decided that we would work the contest as W2RCA. Being in a contest situation meant that rapid TX/RX switching would be a must.

As it turned out the network connection between my home and the RCA event location wasn't quite fast enough for the furious pace of the contest. I was having a hard time getting the remote radio keyed quickly enough to bust the pileups. In some cases I would bust the pileup only to have the target station get frustrated because I wasn't coming back to him fast enough. Not good, not good...

Out of curiosity I turned on my home station and tuned to the same frequency as the W2RCA remote. I found that despite being separated by 2,500 miles I could hear the target station well on both radios! Not wanting to give up on the contest for lack of fast TX/RX switching I decided to try an odd twist on SO2R (Single Operator-Two Radios) setup. I activated transmit on the W2RCA remote station, muted my microphone, and plugged my headphones into my home station. Because SSB is carrier-less mode the remote radio would not transmit any power with the microphone muted.

The next time the target station called QRZ I unmuted my microphone and called him, and heard him come back to me on my home station! I was able to work several stations this way, although there were still a few challenges. First was the effort of keeping the frequency of ftwo radios in sync. Second was some of the stations I could hear clearly on my home station were outside the range of the W2RCA remote station. But in general it worked and was an interesting way to get around the slow TX/RX switching issue.