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-   -   Modified a RCA XL100 CTC108 TV w CH CM7000 inside (http://www.videokarma.org/showthread.php?t=269521)

wa2ise 09-08-2017 04:15 PM

Modified a RCA XL100 CTC108 TV w CH CM7000 inside
 
4 Attachment(s)
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.
http://videokarma.org/attachment.php...1&d=1504904335
And took a picture of the resulting display:
http://videokarma.org/attachment.php...1&d=1504904335
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).

dishdude 09-08-2017 10:27 PM

Nice work! Beautiful set with a beautiful picture.

Findm-Keepm 09-09-2017 03:52 AM

Quote:

Originally Posted by wa2ise (Post 3189276)
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:

http://www.freepatentsonline.com/res...&search=Search

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

old_coot88 09-09-2017 09:33 AM

Robert's modding/hotrodding adventures never cease to amaze. :banana::yes::tresbon:

old_tv_nut 09-09-2017 11:00 AM

Nice!

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

broadcaster 09-09-2017 12:45 PM

Beautiful job!

wa2ise 09-09-2017 06:10 PM

3 Attachment(s)
Quote:

Originally Posted by old_tv_nut (Post 3189319)
Nice!

Thanks all.
Quote:

Originally Posted by old_tv_nut (Post 3189319)
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.

http://videokarma.org/attachment.php...1&d=1505007622
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:
http://videokarma.org/attachment.php...1&d=1505094324
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:
http://videokarma.org/attachment.php...1&d=1505094324

TVTim 09-19-2017 06:30 PM

Nice!

DavGoodlin 09-20-2017 10:42 AM

Amazing!! This beats broadcasting analog - using a STB that is great for DX'ing

wa2ise 09-30-2018 08:48 PM

Did some more on this set, specifically looking at and adjusting the matchup of the luma and the decoded chroma as presented on the CRT display. Found I needed an extra 90 nSec of delay on the luma to get the match looking better.
http://www.wa2ise.com/radios/downline.jpg
a football game down line graphic (green-yellow-green transitions), and below the football captain symbol on the uniform (blue-yellow-blue transitions), showing that the chroma-luma group delay timing is reasonably correct.
http://www.wa2ise.com/radios/capt2.jpg
The setup I used between the CM7000 and the CTC108 circuit board (the video line driver circuit is to buffer the delay line from the unterminated feed to the CTC108 board)
http://www.wa2ise.com/radios/lumadelay.jpg
http://www.wa2ise.com/radios/modifiedCTC108.jpg

old_tv_nut 09-30-2018 10:09 PM

Allen Avionics delay line! - I totally forgot how many of those I used for lab projects at Zenith. Don't recall the exact prices, but it is surely worth more than the TV at this date. ;)

Fun project!

wa2ise 10-01-2018 03:02 PM

1 Attachment(s)
I'm waiting on some 30nsec analog delay lines to arrive.
http://videokarma.org/attachment.php...1&d=1538424133
100ohm, so I'd add a 22 ohm resistor in the luma line from the CM7000, and make the termination resistor 100 ohms instead of 75. As I need 90nSec, I'd use three of these in series.

Got the Allens for about $15 apiece on ebay, plus shipping.

wa2ise 10-04-2018 04:36 PM

3 Attachment(s)
Just got the delay lines, and installed them on the luma delay buffer amp. The delay likes are 100 ohm impedance, so I used a 24 Ohm resistor to the video source to make it 100 ohms. And the delay lines terminate with 100 ohms, then the video buffer line driver makes it 75 ohm impedance again.
http://videokarma.org/attachment.php...1&d=1538688866
and what this buffer/delay line board looks like (I mounted it on the back of the CM7000.
http://videokarma.org/attachment.php...1&d=1538700808
Inside the set now:
http://videokarma.org/attachment.php...1&d=1538700870


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