My Christmas day 9T246 restoration! Almost.....

[dtvmcdonald]

I'm going to hijack this thread, since my "new" 9t246 from the 2013 ETF convention
has a similar problem. This set was recapped and had several resistors replaced
by the previous owner. It basically works perfectly except for horizontal linearity,
which is abysmal. The previous owner had replaced R106 (10k) with 6.8k paralleled
with a rather large capacitor (value unknown since it was several smaller ones
paralled, values hidden in the pile). This kludge made the linearity better but
still poor. I put back in the 10k and it works, bad linearity. He also reported that he
horizontal linearity coil (I presume he meant L42) got hot. It sure appears to me that
it is not getting hot.

Presumably the first thing to do is to take a proper scope home and adjust the
waveform per Sams. Now the questions:

1) Is there a source for the proper waveforms at many places in the circuit?
(E.g. the original RCA schematic and alignments instructions.) I didn't
find one on the net.

2) Since he said the (linearity) coil got hot, maybe it had a short ... are there new ones out there, or at least experience on a proper value replacement. It looks like lots
of turns in one big solenoid. Of course maybe horizontal oscillator alignment will help
things.

3) I seem to remember reading on another forum that the two capacitors C90 and
C91 on the horizontal coil were, on some sets, not the .033 and .05 shown on Sams.
Does anybody know anything about this possibility?

4) On another subject, the input circuit to the tuner seems bizarre. L2 looks like
a balun transformer ... but its not a balun circuit. The input side, presumably 300 ohms, is not balanced, as one side is grounded? What's the idea? I'm feeding it from
either a cable box or a DVD feeding through a VCR as modulator, coax through a good balun. I get fairly large signal increase and an absolutely huge drop in impulse noise
if I ground the shield of the coax to the set chassis. I tried feeding the tuner not
through L2 but direct with 75 ohms and it worked great.

4) The set probably does not have alignment problems, and I don't have
a signal generator, so I probably won't align it. But I had an idea ... I DO have
a good spectrum analyzer. Could I feed Comcast, which has QAM on just about
every channel, flat as a pancake from 54 MHz up to 700, as a signal source and
at least check alignment with a scope probe on the spectrum analyzer? Has anybody
tried this (with AGC set so it doesn't overload.)

Other than these comments, after setting the AGC right it gives an excellent
picture of eggs lying horizontally, or plain TV shows.

Any comments very welcome.

Doug McDonald