Sunday, October 24, 2010

Digital TV Antenna Upgrade

Ok, I admit it right off. There is no difference between a digital tv antenna and an analog tv antenna. But the government has required all over the air tv transmission be digital along with the frequencies of our old channel 2-6 have been given to emergency radio and such, so it appears the antenna should be different.

What I did for our digital tv reception enabling us to be off the cable and off the satellite tv grids was to purchase a better uhf antenna and continue to us the old vhf antenna. For $64 I purchased a uhf DB8 antenna. This antenna has a max gain of 15.8 db. It is smaller than the old huge Archer VU-10 vhf/uhf/fm antenna I purchased from Radio Shack in 1991.

I read on the web where my old Radio Shack #15-1108 antenna amplifier was useless. I had installed it in 1997. I did notice the old amplifier had some corrosion on the cable input and a burnt diode inside. I repaired it but since it is not recommended I went ahead and purchased a replacement. I also read if an antenna is installed in an attic the signal will be cut by 40 to 50%.

For $60.50 including shipping I purchased a Channel Master 7778 Medium Antenna Amplifier. This unit has a gain of 16 db on vhf and 23 db on uhf. Vhf now covers channels 7 through 13 and uhf covers channels 14 through 51. What I need from the antenna amplifier as much as the gain is that the two antenna inputs are combined in this unit without any signal loss and then sent down a single coax cable. Any non powered antenna combiner would loose 3 db which is half the signal strength. So I set the amplifier up in the attic close to the antenna. It is designed to be out in the weather on the mast itself. But in the attic the leads are still at most 20 feet from the antenna. Unfortunately with my old antenna configured for 300 ohm twin lead so I used a impedance transformer just prior to the amplifier which probably cuts the vhf signal some. I did have to throw a switch inside the amplifier to configure the amplifier for use with two antenna’s.

I reconfigured my old antenna with new 300 ohm lead in and installed a new chunk of rotor wire as the old wire that was in the weather had deteriorated to the point of being bare of insulation. I reused the lower 10 foot mast and installed the antenna rotor at the top. Then at the rotor I attached a new 10 foot mast with the new small uhf antenna on top and the old heavy uhf antenna just 3 foot higher than the rotor. We are in a valley so height of antenna helps a lot in receiving a good signal.

At the tv I installed the amplifier power box which sends dc power up the antenna coax cable to the amplifier.

Now it looks like we receive the clearest tv we ever have at this location. We now also get more channels than ever before. On a stormy night it looks like channels 9-1, 9-3, 13-1, 13-2, 20-1, 20-2, 20-3 and 20-5 all come in solid. And solid in digital tv means a really good picture! I suspect 90% of the days we will also receive 4-1, 4-2, 5-1, 5-2, 11, 22-1 and 22-2. Tonight with this storm these later channels are dropping out for 5 seconds every 3 minutes or so. Of coarse there will be a lot of magic in tuning when turning the antenna by the rotor. I suspect we will get 12 if we turn the rotor and what else I am not sure. At the moment 12 is breaking up a lot but the antenna is not pointed in that direction. In life we often leave the antenna in one place. Besides with this many channels why look for more.

So in the end we are quite pleased with the tv configured this way. And to think there is no monthly charge year after year.

HP printer repairs

Gamble Bay Timber’s “HP All-In-One printer” (Series 7400) failed to scan a document. The display indicated the scanner door was open when it was closed and indicated it was closed when the door was open.

Eventually I was able to pop the side covers off the scanning door which is on top of the unit. The covers did not break and did unsnap, amazingly. Inside I noticed the cable harness coming from the lower unit on the rear left. I was able to unplug this cable connector from the top door electronics and then proceeded to remove the back cover allowing me to unsnap the connector from the main body electronics. I was then able to remove this 23 inch cable and observed 3 broken wires where the cable bends routinely each time the door opens.

I further observed the 10 wire cable was secured by tie wraps which were extremely tight. I believe the tight tie wraps contributed to the failure. All the wire bending was at the tie wrap and all the insulation on all the wires were broken at this point. The 3 wire breaks were here also. This printer was purchased in 2006 so is 4 years old.

After some thought I simply soldered the wires together at the break and removed the tie wraps. I also removed a spiral wire protection where the cable bends as the cover is lifted. This gives the wires much more flexibility and the bend radius is increased now.

The printer now is working like new. Later I found out, I could have purchased the whole cover assembly electronics and paper feeding mechanism along with a new cable for $25 from HP. The cable was not sold by itself. Regardless this fix may last longer that the original due to the slight modification.

Our home HP OfficeJet Pro printer (L7555) failed to scan documents but in a different failure mechanism. It would scan the document but fail to place the file on the computers hard drive. Apparently this is a repeating problem either for Vista users or Vista 64 users which is what we have. Finally I found the workaround was to create an icon on the computer which starts up the correct scanning software on the computer and now I start the scan from the computer. I can now locate the scanned document file on the hard drive. I can live with that. I just placed a little note on the printers scan button to direct us to the computers scanning software.

Tuesday, October 12, 2010

TV repair

My nephew’s TV, a Plasma Visio VP322 32" HDTV10A was completely dead, no sign of life when he pushed power button. At first the symptom was it would turn off (after pushing the power button "on") every second or so then on for a few seconds before remaining on. As it got worse, it would take longer "clicking" on and off.

We found several links on the web saying the capacitors on the power board would fail causing these symptoms. The capacitors would actually physical swell. So we dismantled the tv taking the back off which revealed the several interior boards. We saw the power cable entering the center board and found 4 swollen capacitors noting the top of the capacitors were domed rather than flat.

Above are defective capacitors.

We documented them as
C233 10v 3300 microfarad
C234 10v 3300 microfarad
C236 10v 1000 microfarad
C204 25v 1000 microfarad

We ordered up replacements from DigiKey and they arrived first class mail in 3 days for under $8. We then removed the defective ones and installed the new and secured the back cover with at least 30 screws. Plugged the tv in and all works as designed. I was totally amazed. No schematic, no electrical troubleshooting just looked for physical evidence of failure.