the receiver unit we see two coils (arrowed). The top one is part
of a filter which removes the IF at the vision detector and the
bottom one gives a high frequency boost on the output of the video
Both can sometimes
be found damaged and open-circuit. Though usually the break is visible
at one end and a little common sense will soon get it going again.
Both are fine on this
so to the the slog of changing all the capacitors in the receiver
unit, of which there are many, with a lot doing nothing more interesting
than decoupling the heater chain.
This is not a 'hide-inside-old
capacitor' restoration. That would have been an extra-cost option
and is only really worth it with sensitive restorations on ultra-rare
sets (in my opinion). Nevertheless I do my best to be discrete -
for example the bright new polypropylene capacitors are hidden under
black rubber sleeves. The main thing is that the job should be workmanlike.
When all the capacitors
have been changed, all the resistors will be checked and replaced
where necessary, using over-rated modern resistors that are about
the same physical size as the originals.
With the receiver
unit completed, now we turn our attention to the main unit again.
This lonely looking
capacitor on the side can be easy to miss. It feeds the audio that
has just arrived from the sound detector into the volume control.
It is replaced.
At the rear of the
chassis there are two capacitors, here seen replaced. They're part
of a network that distributes the vision signal between the tube
cathode and the sync separator.
The mouldy old remains
of the 'Horizontal Hold' label can be seen to lower left. All such
labels will be replaced toward the end of the restoration.
Here's the frame timebase
component board. Beautiful though these waxed tubular capacitors
may look, they all must be replaced. Even slight leaks here can
cause timebase problems.
A common failure point
is the blocking oscillator transformer, seen to right. Bearing out
my belief that this set is a good one and has been stored in dry
conditions, the windings test OK.
The green power resistors
on the right are nothing to do with the timebase. They are both
part of the main power circuitry and can char the board beneath
if overloaded. Usually this is caused by a leaky series capacitor.
Then you can have a horrible fire risk developing !
all is well in this case. If the board had been damaged, it would
have been wise to mount the replacement resistors above deck for better
cooling. There's invariably some 'darkening' on the chassis parts
immediately above these resistors which at this stage can be conveniently
removed with thinners. It's also a good idea to undo the two securing
screws and look behind the board, to clean it there too and check
all is well.
Once again, here's
another board well worth looking behind. This is the main tag board.
It will mean temporarily disconnecting three wires from its front
And here's what we
see. Another couple of capacitors and a power resistor. This hidden
upper side of the board is invariably dirty too, and will have to
This won't take too
long. Just be grateful it's not a Bush TV1. On that 1948
model the hidden areas really are time-consuming to get at and service.
Although most capacitors
are simply being replaced as discreetly as possible so they reasonably
well 'merge in', those bearing date stamps are more sensitive and
I shall try to preserve them. Here's one example - the 2µF
boost rail reservoir capacitor - in bits. It wouldn't drill out
so had to be split with a hacksaw.
The new capacitor
is hidden inside and everything reassembled around it. Small grommets
go in at the ends and these are sealed with araldite then left to
set. The cable ties are temporary and ensure everything sets nice
When the capacitor
is remounted in the set, the seam will be below and invisible. Naturally,
I've made sure the 'APR 51' marking is opposite to the seam and
will be displayed uppermost.
Here's the underside
with the wiring cleaned and the capacitors changed. The power choke
on the lower right is skew-whiff because it's still unbolted pending
re-installation of the line output transformer.
Next all the resistors
are checked. The only one requiring replacement is the 1.5 Megohm
screen grid resistor on the sync separator (arrowed).