There were no signs of burnt components and no evidence of tampering other
than the double stack selenium rectifier had been replace with solid state rectifiers. I did
spy a fuse that looked to be in the horizontal circuit and a quick check showed it to be
blown. I replace the fuse and decided to apply power, bringing it up with the Variac. Upon
reaching full input voltage the set sprang to life with sound and a nice bright picture, so
looks like all is needed is a recap and the set will be good-to-go.
A copy of the schematic and service data was obtained (Sam's Photofact folder 336-14)
and recapping begun. The unit consists of two very compact chassis which surround the
picture tube neck, and can be separated to some degree by removing the brackets
which hold the chassis together.
Lots Of Capacitors!!
The brackets holding the two chassis together were removed and the chassis was
separated to get a good look at the job ahead of re-capping. There are capacitors
scattered all over, this is going to be a challenge in some areas. Brain surgery might be
easier.
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I started with a group that seemed to be the easiest to access and replace. After several
sessions over three nights, I finally replace the last capacitor. A total of twenty-nine paper caps,
assuming I counted correctly. The photos show the recap with the pile of old caps that
were removed.
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After replacing the paper capacitors, I applied power to the set. Sound but no picture!!
No high voltage!! Time to get out the scope and check a few waveforms. I connected
the scope to the grid of the horizontal output tube and found that it was not getting any
drive signal. Tracing further back to the output of the horizontal oscillator showed plenty
of output there. After some head scratching, the culprit was spotted, I had replaced
a .0012 that connected from the grid circuit of the horizontal output to ground, with a
.047, completely killing the signal on the grid. After installing the correct value cap
the set played properly once again.
Now to tackle the electrolytic capacitors. There are six electrolytics, four of which are
located in a can on the rear of the chassis just above the neck of the picture tube.
There isn't room to cram four individual capacitors into the can, but I can get three of
the smaller value ones in there. After removing the capacitor, I used my dremel tool with a
cutting wheel, and cut along the can just above the mounting ring. The insides were
removed and a 4.7mfd, 22mfd, and 68mfd installed. The can was then resealed with
epoxy.
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The 82mfd, which was too large to fit in the can, was mounted in the space between
the two chassis. A one lug terminal strip was soldered to the chassis just next to the
transformer, the positive of the cap going to this lug and the negative was soldered
directly to the chassis.
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The following photos show the replacement of the other two electrolytics and the solid
state diodes that replaced the selenium rectifier stack. As an aside, when working late
and not paying attention, the last photo shows what happens to an electrolytic when it
is connected with the incorrect polarity.
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With the recapping complete, the set was powered up for a final check-out. Everything seemed in order except the picture
need to be centered vertically and horizontally. This is accomplished by adjust two magnetized rings that surround the
neck of the picture tube, which are located at the rear of the yoke. Access is via a slot in the metal shield which encloses the
yoke and neck of the picture tube. The centering rings have teeth to allow adjustment using the blade of a screwdriver.
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When attempting to adjust the rings, one slipped completely off the plastic retainer and turned freely about the
neck of the picture tube. No amount of coaxing would get the ring to stay on the retainer. Rats!! This means removing
the picture tube to be able to get access to the yoke assembly.
After removing the picture tube, the problem with the ring became evident. The plastic retainer had warped
and shrunk a bit over time, probably due to heat, so the small lip no longer held the ring in place. This was all mounted
to a large ring used to adjust the yoke.
In order to remove the assembly from the neck of the tube, the ion trap had to be removed as well.
The ion trap serves the purpose of preventing ions from striking the phosper on the face of the picture
tube and causing ion burn, which would burn a permanent spot on the face of the tube. The adjustment of
the ion trap affects the brightness of the picture.
As far as the wayward centering ring, all that was needed was something to hold the ring in place on the retainer and allow it to be turned.
I applied a light coating of grease to the inside diameter of the ring, then applied hot glue around
the diameter of the plastic retainer, hoping the grease would keep the glue from adhering to the ring. Not pretty,
but it worked.
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The centering rings were reassembled to the yoke, the picture tube reinstalled and power applied. There was no brightness to the picture, which indicated that
the ion trap needed to be adjusted. There isn't room between the neck of the picture tube and metal shield to reach the ion
trap with fingers, so a plastic tool was inserted, the ion trap was rotated and adjusted back and fourth until
a bright picture was obtained, then the centering rings were adjusted to center the picture.
A few checks of various voltages against the voltage chart was done just to make sure voltages were
within specifications.
Before installing the unit in the case,
the bezel was removed, repainted with gold hammertone paint, and the safety glass and face of the picture tube cleaned.
The photos below show the completed restoration.
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The local PBS station has been running the Jack Benny
television series. I have been taping the shows and enjoying watching them on this little set, just as someone
else may have used this same set to watch the shows live in 1956.
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User's Guide (PDF Format)
