Motorola Color Demod circuits explained

[jpdylon]

I found this while browsing my Sams "Color Tv Guidebook" Its a fairly detailed explanation on how the odd demodulator circuits work in moto color sets. They are using the TS-916 chassis.

If anybody is working on a set with this chassis, i thought it could be useful to someone.

[old_tv_nut]

Thanks for the post - I hadn't seen this article with the full explanation before. Motorola called this the "SODPIL" for "self-oscillating detecting phase injection lock". You really couldn't get accurate color, because the G-Y signal is weaker than it should be. The result was weak greens that tended to brownish or bluish depending on the control settings. Some models of this chassis also included a third customer control that adjusted the DC balance between R-Y and B-Y. This was labeled "TINT". You could adjust this even on black and white programs (since the outputs were DC coupled to the CRT), to get a sepia or blue-tinted picture.

The oscillator part of the circuit is also known as "electron coupled", since it operates between the lower electrodes and its output goes via the flow of electrons to the demodulator grids and plates.

[reeferman]

Didn't Magnavox have a "warmth" control on their late '60s/early '70s sets similar to mentioned "tint" control? Whatever the case, I remember the 3rd adjustment and didn't like it.

[Chad Hauris]

Magnavox had a "chromatone" switch to give the picture more of a sepia tone.
Admiral had a "color fidelity" control to adjust from a sepia to blue tone.
Silvertone called this a "chromix" control.

[old_tv_nut]

I have a '67 Magnavox with the Chromatone switch, and I agree that it's not worth it. Reminds me of a quote from an old Zenith engineer on seeing the first color chassis design: "27 controls, each one making it worse!"

[oldtvman]

The only benefit I can remember from Motorola was the soft picture that seemed to be just the right fit with older customers. I guess that's why they also didn't pay too much attention to the color accuracy of the Motorola sets.

[andy]

...

[old_tv_nut]

Originally Posted by andy

Sounds like the color temperature control most modern TVs have.

A real color temp control changes the color of all whites and grays equally, that is, it's a gain adjustment of R,G, and B. Those old controls changed the DC voltage of R and B, and actually caused mistracking of the gray scale.