4. ADJUSTMENT PROCEDURE
1.
Adjustment of output offset voltage
1)
Remove the MAIN-IN and PRE-OUT plugs, and
connect a digital voltmeter set to the DC range to the
speaker terminals with no signal and no load on the
unit.
2) Adjust R622 for L-ch and R722 for R-ch until the
indication on the digital voltmeter is ±10 mV.
2.
Idling adjustment
1)
With no signal or load on the unit, short TP-1 and
TP-3 on the P.W. Board (PN00).
2) Connect a digital voltmeter set to the DC range be-
tween J607 and J707 and adjust J643 and J743 for
36 mV.
3) Remove the short between TP-1 and TP-3, and R642
and R742 so that the voltage between J607 and J707
is 180 mV.
3.
Adjustment of quarter "A"
1)
Connect a DC voltmeter between the emitter and base
of QL07 for L-ch. (The meter range is greater than
100 V, with the polarity of the emitter (+) and base
2)
Connect the oscilloscope between TP-1 and TP-2 on
the P.W. Board, and monitor the waveforms at TP-2
with TP-1 as the reference.
3)
Connect an 8 ohm load to each of the speaker termi
nals, and input a 1 kHz to the L channel MAIN-IN.
Adjust the input level so that the load on L-ch gives
output of 17 V.
4)
Rotate RN40 (RN41) on the P.W. Board (PN00) and
monitor the waveforms on the oscilloscope.
5)
Adjust RN42 (RN43) so that the pulse width is the same.
6) Adjust RN40 (RN41) again to make the pulse
width 0,1 ms. Confirm that the voltage at the
emitter of Q107 is 63 V.
7) Lower the input signal and confirm that the voltage
at the speaker terminal is 16 V — 16,5 V and the
voltage at the emitter of QL07 is 29 V at the point
where the pulse disappears.
8) Next, connect the DC voltmeter between the
emitter and base of QL08 for R-ch. (The meter
range is greater than 100 V, with the polarity of the
emitter (
−
) and base (+).)
9) Input a 1 kHz to the R channel MAIN-IN. Adjust
the input level so that the load on R-ch gives
output of 17 V.
10) Adjust items 4 to 7 in the same manner as L-ch.
The adjustment locations are those shown in
parenthesis.
