DECCA CS1900

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The initial condition was no e.h.t., with the PL509 line
output valve red hot. While testing, the 470Q resistor R500
on the convergence board, in series with the line windings
on the pincushion distortion correction transductor, burnt
out. With this resistor open -circuit the line output stage
came back to life. The resulting picture was nearly normal
except for a small amount of distortion at the top of the
screen. Replacing R500 brought back the original fault, the
resistor running hot and soon burning out. If the screened
lead to the convergence coils is unplugged the line output
stage returns to life – but without line scan of course since
the line scan circuit is open -circuit, the line scan and
convergence circuits being in series.
The fault is almost certainly due to a defective
transductor loading the line output stage. The part number
is 550717. (Decca interim single -standard colour chassis.)

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