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Got the chroma reference oscillator fixed. It's an oscillator design that is new to me, and is quite sensitive to the value of a "choke" in the control signal from the phase detector back to the oscillator to adjust its frequency. Although Sams calls it a "choke," that is quite a misnomer -- it's actually really an inductor with a specific value affecting some RF response on the control line. Put in a coil much more closely matched to the original and got it running OK.
Still no color, however, so I ran some checks on the video alignment, and found things are not even close. This explains the lack of chroma sync burst on the detected video and so-so sharpness on the black and white picture (apart from focus issues). It appears that virtually every slug on this set has been fiddled with in the past. It's got traps in the middle of the passband, the wrong center frequency (by more than 2 MHz!), a generally peaked (rather than flat) and narrow passband shape, and worst of all, one of the little IF coils in the tuner pushed inside the tuner and damaged (core cracked and stuck). I'm repairing that coil -- nice that that top of the tuner comes off so easily for service.
Alignment looks like it will be very time consuming... and may uncover some additional problems.
Convergence transformer arrived today, so that is also ready for attention. Lots to do.
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11-22-2013, 02:01 AM
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