Section 2 Mechanical Adjustments; Section 3 Electrical Adjustments - Sony BM-21 Service Manual

BM-21/23
SECTION 2
MECHANICAL ADJUSTMENTS
PRECAUTION
1. Clean the following parts with a denatured-alcohol-moistened
swab :
playback head
capstan
pinch roller
2. Demagnetize the playback head with a head demagnetizer.
3. Do not use a magnetized screwdriver for the adjustments.
4. The adjustments should be performed with the rated power
supply voltage (3V) unless otherwise noted.
• Torque Measurement
Mode Torque Meter
FWD
CQ-102C
FWD
Back Tension
REV
CQ-102RC
REV
Back Tension
FF
CQ-201B
REW
• Tape Pulling Force Measurement
Mode Torque Meter
FF CQ-403A
REW CQ-403R
8
rubber belts
idlers
Meter Reading
2.06 – 3.72 mN•m
(21 – 38 g•cm)
(0.30 – 0.52 oz•inch)
0.05 – 0.29 mN•m
(0.5 – 3 g•cm)
(0.01 – 0.04 oz•inch)
2.06 – 3.72 mN•m
(21 – 38 g•cm)
(0.30 – 0.52 oz•inch)
0.05 – 0.29 mN•m
(0.5 – 3 g•cm)
(0.01 – 0.04 oz•inch)
more than 60 g•cm
(more than 0.84 oz•inch)
Meter Reading
more than 40 g
(more than 1.42 oz)
SECTION 3
ELECTRICAL ADJUSTMENTS
PRECAUTION
1. Power supply voltage : 3V
Test Tape
Type Signal
WS-48A 3 kHz, 0 db
Tape Speed 4.8cm/s Adjustment
Switch position
TAPE SPEED Switch : 4.8 cm
Procedure:
test
WS-48A
(3 kHz, 0 dB)
set
1. Play back WS-48A (tape center portion) in FWD mode.
Adjust the RV601 so that the frequency counter reads 2,980±
30 Hz.
2. Play back WS-48A (tape center portion) in REV mode.
Confirm that the reading of frequency counter is within 2.5 %
from the reading in step 1.
Used for
Tape Speed Adjustment
frequency
counter
18 Ω
J102
EAR