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The
RF/IF chassis is removed and here is the underneath. The view
is quite similar to on the earlier TV22 but this version uses
9-pin EF80 valves rather than 7-pin EF91's.
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A preview
of where much of the future work will take place, with this underneath
view of the main chassis.
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The
chassis parts now receive their preliminary wash in a detergent
solution, to remove the worst of the dirt. This is helped along
with a stiff brush - and WD40 when there are waxy deposits. I
have recently got Parkinson's Disease and can now call upon its
shaking feature for more intense brushing!
There
are no exceptions... the line output transformer and other coils
and chokes are washed too. However, all are thoroughly blown over
with compressed air straight afterwards.
Here
we see the focus magnet being dunked...
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I've
been thinking more about the eventual use of this set. It would
be nice if I could once again view my collection of old 405-line
and 625-line VHS cassettes. There's some priceless archive materials
amongst them. There's another row of them hidden behind this lot.
So
I've decided to include baseband 405-line and 625-line inputs
as well as the normal Channel 1 405. The set will be switchable
between the three modes. Stay tuned to see how this is done...
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During
cleaning and examination of the LOPT, I discover the whisker of
wire that runs from the EHT overwind to the EHT rectifier has
come adrift.
Now
this may be my fault, due to carelessness. Anyway the rule
is "if you broke it you fix it". There is now nothing
visible left of the end of the winding, but after melting the
wax with a soldering iron and some gentle prodding around I think
I can see a tiny wire hair about 1mm long that represents what
I am looking for.
I pass
a new connecting wire through the EHT rectifier's mounting hole
and curl it over the top of the board to discourage it from moving
during soldering. Then, ( 'X' marks just below the spot) the new
wire is bent to the exact position and solder applied.
At
the second attempt, it works! I can see the correct 350-ohm reading
across the overwind. But only actual use will prove whether this
repair proves durable.
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Here's
the LOPT with the rotten valve top cap feed wires replaced and
a new EY51 EHT rectifier fitted.
Elsewhere,
I've replaced the perished wires feeding the frame scan coils
with new rubber wires of the correct colours.
All
the little sub-assemblies that were removed from the chassis are
now serviced.
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The
perished remains of the speaker leads, seen at the left side of
the transformer, are now pulled off.
The
purple covered main carrying lead, to the upper left, is in dangerous
condition and will be replaced in due course.
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I now
carry out a survey of all the capacitor values and quantities
that will be needed to complete the job. Here is the list being
compared in stores. It turns out I have enough of everything in
stock...
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One
capacitor harder to source would have been the main (double) HT
smoothing electrolytic. However both parts of this prove susceptible
to re-forming. This is carried out overnight.
Here
we see, toward the end of the process, the higher capacitance
(250uF) section showing a leakage current is down to 181 uA. This
figure is very good.
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Next
job, to re-cap the RF/IF unit...
The
pot toward the middle is the Vision Interference Limiter. In practice,
this won't be used but nevertheless it is pumped full of Waxoyl
to prevent any future scratchiness.
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But
what's this? Someone has snipped this capacitor connection in
the past.
This
is actually one of the heater chain decoupling capacitors and
doesn't do very much. It will be replaced later anyway.
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All
the waxies underneath are duly replaced. This is to be a set that
will be in regular use and I don't want it going wrong regularly
as the price for maintaining strict originality.
Dirt
is removed from crannies with a Q-tip impregnated with WD40. The
valve bases are also sprayed with WD40 before wiping over. This
will have a temporary effect on their electrical characteristics
but they will have dried out and be back to normal long before
the set is switched on.
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Around
now, all of the many pots on the chassis are injected with waxoyl,
for a scratch-free future.
The
final heater chain dropper lives underneath on this set and must
have been gently smoking at one time, since there is a black deposit
on the chassis above, all round it. The dropper is temporarily
removed - here's the mounting hole - and the deposit cleaned off.
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This
is the original frame output cathode decoupling capacitor. It
is returned to +HT, not 'deck'. I am not sure why this is, though
doing it this way will tend to cancel any HT hum on the frame
scan. It is replaced.
Note
the 'Oct 53' date on its case. This set would not have been in
the shops in time for the Coronation!
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Next
this gubbins must come off! This is the back view of the mains
adjustment dropper assembly. The rubber wiring will be mostly
replaced.
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Getting
it off involves removal of some other parts underneath to give
access to the mounting screws. In general the purple mains-carrying
rubber insulated wiring is in perished condition and will have
to go.
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