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ALIGNMENT PROCEDURE
A. DC OFFSET VOLTAGE
The DC OFFSET between OFFSET Test Point and AGND must be within 0+/-20mV.
B. IDLING CURRENT
The idling current in the output stage of the poweramp should be set to 30mA+/-5mA per
pnp-npn transistor pair (This means the mid point voltage is 6.6mV with down limit of
5.5mV and up limit of 7.7mV). The alignment procedure is: At first, adjust RV102 (Marked
as "Idling Current ADJ" in the drawing page 6) for a voltage of 6.6mV +/- 1mV between Test
point 1 and 2. Then pre heat the unit for 1 minutes, let idling current settled and then readjust
to 6.6mV +/- 1mV. This is a no-load adjustment.
Pls note: Though the idling current is set as 6.6mV +/-1mV during the adjustment, due to the
influence of varied ambient temperature and mains voltage etc., the idling current will drift after
some time. During the normal checking of idling current in the service field, it's acceptable as
long as the voltage is in the range of 5.5mV—7.7mV.
C. ISC SENSITIVITY
The ISC sensing voltage can allow 0mV+/-50mV. But, for the alignment process in our
factory, we tighten the limit to 0mV+/-10mV. That is to adjust Pot RV103 (as marked as
"ISC SENS ADJ" in the drawing page 6) to get a voltage between the "ISC SENSE TEST
POINT" and AGND to be 0mV+/-10mV.
D. MINIMUM VOLUME LEAKAGE CANCELLATION
The volume control, 20k potentiometer has a finite end stop resistance, variable and about
7 ohms max, so at minimum volume there is some signal leakage to pre out, appearing 29
dB higher at poweramp out. The cancellation circuit applies a fraction of the signal to the
negative input of the line out amp to cancel this leakage. The alignment procedure is: feed
1KHz/2V signal in CD. Set volume for 10V speaker out as 0 dB reference. Then set vol to
minimum. Adjust RV307 (Marked as "LEFT MIN. LEAKAGE ADJ" in the drawing page 7)
for a minimum at left speaker out, the reading should be < -86 dB, or 0.5mV. Adjust
RV308 (Marked as "RIGHT MIN. LEAKAGE ADJ" in the drawing page 7) for a voltage
minimum at right preout, the reading should be < -86 dB or 0.5 mV.
E. FREQUENCY RESPONSE
The frequency response should be set to 0+/-0.3dB. The alignment procedure is: Disable
tone defaet first, feed 1KHz/2V to CD, Adjust Preout to 500mV as 0dB reference level.
Change to 20Hz and set RV305 (Marked as "LEFT FREQUENCY RESPONSE ADJ" in the
drawing on page 7) to within +/-0.1dB. Then repeate the above for the RHC, adjust RV306
(Marked as "RIGHT FREQUENCY RESPONSE ADJ" in the drawing below) to within
+/-0.1dB.
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