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post #41 of (permalink) Old 2005-11-07, 08:49 AM
Join Date: Sep 2005
Posts: 17
Overdriven Channel Master 7775 Pre-Amp = LESS SIGNAL

So in my search of NBC and UPN, I went ahead and purchased a channel master 7775 preamp from Sal's TV in scarborough.

As a refresher I'm receving all of the Toronto stations ok, and receiving almost all the Buffalo stations ok with the exception of NBC (WGRZ) and UPN. (As a side note, 7-1 seems to have disappeared since yesterday) I'm located in Toronto, up on Avenue and Lawrence. My setup is a CM-4228 with 30ft of cable to a samsung CRT with (H)DTV tuner built-in -- no splits or anything.

So I get up on the roof and put the 7775 in. Mike at Sal's tells me that the preamp is probably overkill, but will help on the really snowy days. Turns out that on EVERY single channel the power level to my Samsung TV is 10 - 20% worse! This includes CBC, and CTV which are coming in at 90%. I verify connections, and I verify that the amp indeed is 'doing' something. If I remove power to the power injector, power levels drop an additional 20%. But if I plug it in again power levels go up, but never to as high as they were without the preamp. With the preamp not do I not receive NBC (Which I steadily receive 1 bar but no picture), but I also loose WUTV (29-1) and ABC (4-1) comes in choppy if even at all. After a good 2 hrs of testing, it appears as though if the mast-mounted preamp is installed I immediately get a huge insertion-loss... (About 20-30%) whether or not it is powered.

Has anyone had this behavior before? There isn't much to my setup, nor is there anything to configure on the CM-7775 so it looks like I'm stuck with a bad preamp?? Suggestions?

Also as another aside (I'm an electrical engineer) I took apart the 7775 -- these things are a 2-sided hand assembled pcb! It's no wonder they cost this much!?! Also ... it appears as though the bottom half of the pcb is non-populated? It's a wonder why CM does not offshore this assembly ... we could have this preamp for less than $20...
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