Sinclair MTV1 service manual V2.1 Page 34 of 39
SETT
ING UP PROCEDURES
Set up -45 volts
Connect a meter between Pin 7 of Berg socket and Earth (chassis ground).
Adjust preset pot for -45V. If you have to make more than a very slight adjustment, investigate the
reason why. This rail usually doesn’t drift much with time. It should also be a smooth rail; if there is
line or frame frequency ripple then replace the 4µ7 capacitor C436 (marked on the coloured circuit
diagram as ‘-45V smoothing’).
Set heater volts
Connect an RMS meter between link marked X and earth. Adjust pot for 0.55 volts RMS.
It is important to use a true RMS meter here because the heater supply bears little resemblance to
a sine wave; using a ‘normal’ meter will give an incorrect reading. Rule of thumb: if the tube lights
up, and you haven’t performed any major surgery, then you don’t need to adjust the tube heater
volts. If the tube doesn’t light up, and you don’t have a true RMS meter, check for the presence of
some AC voltage across the heater pins on the tube (tube pins 1 & 2, or tube board pins c & d).
Other adjustments, width, height etc
Fairly obvious but advisable to check -45V after carrying out any such adjustments.
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General