Dc Balance; Idle Current - Pioneer SX-1280 Service Manual

1 0 . 3 P O W E R A M P L I F I E R
Turn VR2 (L and R) fully around in the counter-
clockwise direction, but set VRr (L and R) to the
center positions. Without any load or input signal,
tum the POWER switch ON.
Since the same configuration is used for both
Ieft and right channels of the SX-1280 power
amplifier assembly, the following adjustments
apply to both channels.
D C B a l a n c e ( F i g . 2 3 )
Adjust VR1 so that the potential differnence
between terminals No. 14 and ground reads zero
volts (to within t20mV). If this level cannot be
attained, disconnect the jumper leads A (or recon-
nect if already disconnected), and then readjust.
ldle Current (Fig. 23)
Adjust VR2 so that the potential differnece
between the plus (+) terminal No. 17, and the
minus (-)
terminal No. l-1 reads 15mV (or at
least in the 10 to 25mV range). The potential
difference between + terminal No.18, and - ter-
minal No. 12 should also register about 15mV at
this time. After passing a current for about 10
minutes, check these voltage readings again.
L c h a n n e l
A
V R r
- N o . 7
N o . 1 4
N o . 1 2
N o . 1 1
1 0 . 4 M E T E R A M P L I F I E R
Apply a TkHz signal to the POWER AMP IN
terminals (or any other power amplifier input
terminals). Adjust the level of this input signal so
that the voltage on the output terminals (SPEAK-
ERS) reads 3?.95V rms (AC). Then adjust VRr(L)
and VR, (R) of the meter amplifier assembly so
that the output power meters read 180 watts.
F i g . 2 4
R c h a n n e l
N o . 1 1
N o . 1 2
N o . 1 4
N o . 7
V R z
V R r
A
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3 0
P o w e r a m p l i f i e r
F i g . 2 3