View Full Version : Modified a RCA XL100 CTC108 TV w CH CM7000 inside

09-08-2017, 05:15 PM
Had an older RCA XL100 TV set that used a mechanical click twist tuber (not a varactor or synthesized tuner). And had an extra Channel Master CM7000 CECB with S-video output. I decided to make this TV into a digital ATSC receiver by removing its old tuner and installing the CECB inside it. What this would do for me is to create a color TV set with no cross luma cross chroma defects (no false color crawlies on fine luma detail, and no crawling or hanging B&W dots on color transitions in the video image). What I worked hard at RCA labs to reduce with the then broadcast analog NTSC TV signals. As the Channel master CM7000 provides S-video outputs (the luma and chroma never been merged together, thus no cross signal defects later). Downloaded the SAM's ($22 but was worth it to find my way around the TV circuits) and found the points to inject the S-video and the notch filter on the luma I'd want to remove. Paid attention to be sure the demodulated chroma would match the luma on the display screen CRT. Also had to figure out how to get the audio into the sound IF demod and audio amp chip.
And took a picture of the resulting display:
No cross luma or cross chroma problems, as these were never mixed together in the first place. Digital TV ATSC transmissions keep these signals separate.

The CTC108 chassis is a "hot chassis" design, so I used a special antenna RF coax connector that stops DC and low frequency AC, but lets pass 50MHz and above from the antenna to the box (which is now "hot" inside this modified set).

09-08-2017, 11:27 PM
Nice work! Beautiful set with a beautiful picture.

09-09-2017, 04:52 AM
Had an older RCA XL100 TV set....

Which no doubt has one or more of your patents included? If so, how cool is that?!?!:D

For those that don't know, Bob is our resident Edison: :thmbsp: :thmbsp: :thmbsp:

Very nice work and informative too - thanks for the share!

09-09-2017, 10:33 AM
Robert's modding/hotrodding adventures never cease to amaze. :banana::yes::tresbon:

09-09-2017, 12:00 PM

Did you have to amplify the luma or chroma, or did you get what's needed due to not terminating the outputs?

09-09-2017, 01:45 PM
Beautiful job!

09-09-2017, 07:10 PM

Thanks all.

Did you have to amplify the luma or chroma, or did you get what's needed due to not terminating the outputs?

The luma and chroma signals were about the amplitude needed, unterminated. You can get away with doing that as any reflections bouncing off the unterminated far end of the connecting coax cable gets absorbed by the source termination (the 75 ohm resistor located at the signal source).

Ended up using an audio isolation transformer on the audio from the CM7000 CECB. The deflection yoke magnetic fields gets into everything, and this transformer breaks a loop to avoid excessive buzz in the sound. This loop includes the luma and chroma cables from the CECB to the chassis.

Used the TV's original volume control's power switch as a master power switch that unpowers the set and the CECB. I noticed that CM7000's can go into la-la-land if left in standby for weeks on end. If that should happen, I can turn off all power with this switch. Left the CECB's top off to allow for better cooling of its boards.
Added a plastic light pipe to direct the LED light from the CM7000 board to a point in the center where the VHF knob used to be. So I can see the status of the CM7000 board, green = on, yellow = standby and rest of set off, red = power up boot. Black = all off.

More screen shots showing a lack of cross chroma, below a pattern on the collar that gets cross chroma with a line comb:
And a lack of cross chroma (look at the close together strips to the left of "Fox Sports") you'd get with a notch filter:

09-19-2017, 07:30 PM

09-20-2017, 11:42 AM
Amazing!! This beats broadcasting analog - using a STB that is great for DX'ing