Sharp GF-777H - Electrical Adjustment

ELECTRICAL ADJUSTMENT
Figure 11-1
Record Amplifier Bias Current/Bias Oscillator Frequency
Adjustment
1) Connect a VTVM to both ends of the resistor (R453 or
R454) on the record/playback amp. printed wiring board.
2) Set the function selector switch to ‘tape’, the deck-2 tape
selector switch to “‘Normal’’ and the best interference
canceller switch to “A” position.
3) Connect an oscilloscope (the vertical input) to the output
of VTVM, and an audio generator to the oscilloscope (the
horizontal input).
4) Place the unit in record mode, and check that the bias
oscillator frequency, on the oscilloscope Lissajou’s figure, is
76 to 84kHz. Next by setting the beat interference
canceller switch to “’B” and “‘C” positions, the range of that
frequency must be within —1.541.0 kHz and —6£1.5 kHz
in respective positions.
5) Adjust the bias current adjust semi-variable resistor (VR451
or VR452) so that the VTVM reads 4.4 mV.
Erase Current Check
1) Connect the VTVM between the test point TP451 and
TP452.
2) Set the function selector switch to ‘‘tape’’, the deck-2 tape
selector switch to “Metal” positions.
3) Place the unit in record mode, and check the at the VTVM
is reading 135 to 185 mV.
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Figure 11-2
Figure 11-3
VR451 VR452
Bias Current
Oscilloscope
Audio generator
Record mode Oscilloscope
Figure 11-5
4g