Service manual

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ADJUSTMENT PROCEDURES
NOTE:
The tuning and other functions rely heavily on accurate power supply voltages.
Always be sure the + and - 10 volt supplies are properly set before making other adjustments.
* Digital voltmeter with 0.1% accuracy
TO ADJUST . . . FOLLOW THIS PROCEDURE . . .
+10 volts Connect an accurate D.C. voltmeter* to pins 1A and 2A on the
oscillator (board 1). Adjust the +10 volt trimpot on the power
supply (board 3) for +10.00 volts.
-10 volts Connect an accurate D.C. voltmeter* to pins 2A and 3A on the
oscillator (board 1). Adjust the -10 volt trimpot on the power
supply (board 3) for -10.00 volts.
A-440 Ref. Oscillator Turn on A-440 and allow to warm up for two minutes. Adjust
A-440 trim-pot on the filter (board 4) for zero beat with an "A"
tuning fork. By bringing the struck tuning fork in physical contact
with the shell of a pair of headphones, while listening to the A-440
output, the beat note becomes more audible.
Oscillator Tuning
(With Equipment)
Connect a frequency counter to the High Main Output jack.
Set the PITCH WHEEL to center, TUNE control to 0, RANGE
switches to 2 ft., WAVE-FORM switches to SAWTOOTH.
Set MIXER VOLUME controls to 4, turn OSCILLATOR
MODULATION switch off, and OSCILLATOR 3 CONTROL
switch on. Set Oscillator 2 and 3 FREQUENCY controls to mid-
position. Turn on OSCILLATOR 1 mixer switch. Adjust
Oscillator 1 Range Trimpot
for 3520 Hz while holding high "A"
key down. Depress low "A" and hold while adjusting Oscillator 1
Scale Trimpot for 440 Hz. Repeat until no further improvement is
attainable. Turn off OSCILLATOR 1 Mixer switch. Turn on
OSCILLATOR 2 and repeat the procedure -- then OSCILLATOR
3. Finally, check tracking between any two oscillators and make
any necessary touch-up adjustments to improve tracking.