My "New" CT-100 restoration

[dtvmcdonald]

The recap of the paper and tubular electrolytic caps is done. I still have the chassis
mount caps in the power supply and at the front of the set opposite the tuner to do.
I'm going to do the latter set today, then I have to make mounts for the
power supply ones. I'm not restuffing them.

After seeing the chassis bottom after the recap, I'm quite happy with its
look. Its not original, but it sure looks neater and not so cramped. I'm
not happy with the look of the blue rectangular caps I had to buy for some values,
like 0.001 or 0.0022 at 1600 or 2000 volts.

I'm going to look for better looking ones, either Panasonic brown or
axial lead. I assume that mica or polypropylene would work. Is that correct?
The blue ones I have are rated for RF current use, which their spots are used for
(well, overtones of the sweep frequency.) Any suggestions?

[dtvmcdonald]

Sunday (the 27th) I completed the recap except for the B+ supply.
Monday I designed and built a B+ supply replacement
for the SE diodes and the four big chassis filter caps.
A picture is attached. One of the four replacement caps
is visible, the other three are behind it and not clearly
visible.

After finishing, I inspected the chassis for about 20 minutes
for shorts and solder blobs. At this point there were no tubes or yoke.
I connected it to a Variac and slowly raised to B+ to 50 V [sic]
with no problems and let it sit for 30 minutes. The voltage
was monitored on a scope. Then I slowly
raised the voltage and at 140 I heard a "pop"
from the horizontal sync section. I turned off the power and
spent another 30 minutes inspecting, finding one solder
blob and one pair of tube pin connections that looked
a little too close, and fixed them. After that the B+ went to
240 with no problem. I didn't want to go too high with no load
since the nominal +385 and +285 were actually the same.
I then connected the yoke and purity coil and tried again, with no
problems at 220 v B+.

I then put in all the tubes but removed the ballast. Turning
it on produced filaments and no problems.

I reinserted the ballast. At this point I had a scope on the
400v B+. I set the Variac to 105 volts with it off and threw
the switch (did I mention the one on the set is broken,
stuck on.) Nothing awful happened: the voltage went up to about 370
and then down a bit. I checked the other B+ supply
voltages (385, the two 285s, the 200, and the -30). All were
as expected a bit low. Turning the Variac to 117 produced
reasonable values. Focus voltage was very roughly 8 kV and
HV was somewhat low at 15 kV. I turned off all lights in the room to look
for red plates and saw none, including the HV rectifiers and regulator
tube. Also, no bad smells.

At this point I hooked up my Ch. 10 transmitter and installed
the channel selector knob. It was not on 10. At this point
a minor disaster struck ... turning the channel selector knob
produced no clicks. Turning hard I got it to 10 ... just as the knob
broke. The crack is probably fixable.


I tried looking at the signal with a scope to the green signal to the CRT
and saw only hum. I then tried looking at the grid of the audio
output with the scope (the speaker is not connected). All I
saw was horizontal sync pulses.

At this point I decided to try a sweep generator. I connected the
scope to the test point at the video amplifier grid. Turning to Ch. 10
produced a passable result. So the tuner did change to Ch. 10.
I reattached the RF signal (of Letterman) and was rewarded with ....
AUDIO??? Yes, audio. It was clearly Letterman,
since the waveform followed the sound from my flat screen.
Perhaps bad fine tuning?
I installed the fine tuning knob and was rewarded by a
good video waveform. This is of course a big milestone!

At this point I checked for sweep from the yoke (clearly there
was horizontal there, since the scope probe picked it up.)

To do this I set the scope for X-Y with no sweep or signal , just
a dot in the center. I set the yoke on the scope
(which had the screen facing upwards)
with the set off and turned the set on. Soon I was
rewarded with a raster about 5/8 (H) x 3/16 (V) inch. Another
good milestone.

Finally I looked for sync. I put the scope on dual trace,
Ch. 1 to the test point, ch. 2 to a scope probe connected
to nothing (picking up horizontal sweep). Scope sync was to Ch, 1;
I could not get the TV to sync to the signal. I measured the sync pulse timing:
as expected 6.4 divisions. I switched sync to Ch. 2 and
measured the period: 6.0 to 6.2 division was the whole
range of the horizontal sync control: no wonder it did not sync.
A repair will be needed.

Then I moved the Ch. 2 to a test lead wrapped around the
vertical sweep tube and repeated the above, but synced to
the power line. The vertical was easily adjusted to be in sync,
though the range was narrow. A scope trace is attached.

That's enough for yesterday (its now 1 AM).

Doug McDonald