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At
this point the four-way mains cable to the on/off switch is replaced.
The yellow-clad screened sound volume control wiring is in shocking
condition and awaits attention.
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The
new on-off and sound volume wiring has now been fitted. The black
cable carrying the mains is now screened for still better hum
supression. The length of this cabling is generous, since it will
have to reach further than before in the Baird console cabinet.
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Time
now to get 'down and dirty' as I unscrew the component board fastenings
to have a peep underneath.
I particularly
want to see if there are any components, normally invisible, hidden
underneath the boards.
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The
real problem turns out to be perished hidden rubber wiring. This
could be carrying dangerous voltages.
This
is a good reason, in my opinion, why it's always better to do
a thorough job, rather than simply replace the components necessary
to get the set to 'work' - as some advocate.
The
brown 'gunk' from long-smoking power resistors is unsightly too,
and I'll try to clean it off.
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It
turns out the wiring is only perished near the heat-producing
power resistors. It would be a right royal pain to un-loom and
replace all the wiring, so I simply link in new rubber wires of
the same colour, where necessary.
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Here's
the underneath of the main chassis re-capped. This is not a rare
or valuable set so the new capacitors are not hidden inside the
old.
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A
new width control - a power potentiometer - is fitted.
The
wirewound track on the original one had come adrift.
This
control mainly works by varying a shunt across the line deflector
coils. The new pot is 50K, replacing a 30K. This will be OK. The
nett effect will be to give this control a little more travel.
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Finally
the resistors are checked. It's normally the higher value ones
that go 'high'.
A bit
of 'highness' is normal though. This 2.2 megohm resistor reads
about 3 megohms. I check the schematic to see what it does...
it feeds the tube first anode so should not be too critical.
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The
valves are now all tested and the good ones cleaned up. Only two
of them need replacing: one of the EF80 valves from the IF strip
and the PL83 sound output.
I'll
get the chassis working in standard trim for now, but later on
the PL83 sound valve may become superfluous. I expect to be adding
a separate valve amplifier unit for higher quality sound.
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The
line output transformer assembly clips back in and the three valves
behind it are plugged in... from left to right these are: the
PY82 HT rectifier, the PL81 line output, and the PY81 boost rectifier.
The
PL81 displays the usual brown marks inside the glass but actually
tested fine. I take the view that a 'burned in' but proven valve
like this is likely going to be even more reliable than a new
replacement.
The
(horizontal) EY51 EHT rectifier has been changed previously.
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The
LOPT assembly shielding panel is now secured with its one screw
and fibre washer. This is situated a little close to the PY82
HT recifier in my opinion - hidden here behind the panel on the
far left.
You
may be able to see that I've painted the internal surface matt
black, to absorb the heat from this valve, rather than throw it
back by reflection.
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The
tube and its ancillary parts are mounted up. Next, I mustn't forget
to plug in the scan coils.
The
ion trap magnet is cleaned and placed at the end of the tube neck
in a 'guestimate' position. The pointer on it (not visible here)
points toward the screen. This is the other way round from how
it was originally!
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Same
old problem though... how to safely secure the front of the tube!
This cable tie arrangement will have to do for now.
Just
holding the tube by its neck clamp - as per the design - will
be insufficient when I start upending the chassis during final
fault finding.
This
unpleasant feature clearly shows that the TV24 variant was an
afterthought; an attempt to adapt the short 9-inch TV22 chassis
for a 12-inch tube.
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The
next morning I've made up a couple of temporary brackets to secure
the tube and mask at the front.
These
will be removed just before the chassis goes into its new cabinet.
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Right,
now to switch on!
Before
doing this, past experience has taught me a quick check of the
wirewound pot tracks is a good idea. Breaks in these often cause
the first faults to be found.
I run
around them with the Avo... This is actually the Brightness pot.
When taking this photo I thought it was the Frame Hold! You live
and learn...
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You
see, to start with the tube seemed to be cut off and I could only
get a raster by placing an Avo prod on the tube cathode. Strange...
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