Sony HP-210 - Ae Power-Amplifier Adjustments

Tracking Alignment
1.
3-6.
Tune the set to the station whose carrier
frequency is closest to 620kHz and adjust
the position of antenna coil L401 as shown
in Fig. 3-11 to obtain maximum output.
Tune the set to the station whose carrier
frequency is closest to 1,400kHz and adjust
antenna trimmer CT401 to obtain maximum
output. See Fig. 3-11.
Repeat the above steps two or three times.
POWER-AMPLIFIER ADJUSTMENTS
Note: There are two adjustments in the power
amplifier. One is dc bias adjustment
and the other is ac balance adjustment.
These adjustments should be alternately
repeated two or three times after
replacing any of the power-amplifier
transistors until the best operation is
obtained.
_ De-Bias Adjustment
Serious deficiencies in performance, such as
thermal runaway of power transistors, will result
if this adjustment is improperly set.
CAUTION
To avoid accidental power transistor
damage, increase the ac line voltage
gradually, using a variable transformer,
while measuring the voltage across the -
test points (emitter of Q508 to ground).
See Fig. 3-17. Check to see that the
reading does not exceed 15mV. If it
does, turn off the power as soon as
possible, then check and repair the
’ trouble in the power amplifier board.
Test Equipment Required
1. De millivoltmeter
2. Variable transformer
3. Screwdriver with 3 mm (1/g”) blade
Preparation
1. Remove the record changer as described in
Procedure 2-4.
2. Connect the dc millivoltmeter across the test
points as shown in Fig. 3-17.
R-CH
test point fm
Fig. 3-17. De millivoltmeter connection and parts location