Sony LBT-A790 Service Manual page 104

SECTION 3
ADJUSTMENTS
3-1. MECHANICAL
ADJUSTMENTS
2.
Turn the adjustment screw and check output peaks. If the peaks do
not match for L-CH and R-CH, turn the adjustment screw so that
Precautions:
outputs match within | dB of peak
1
Clean the following parts with a denatured-alcoholmoistened swab;
record/playback/erase head
pinch roller rubber belts
capstan idler
Demagnetize the record/playback head with a head demagnetizer.
(Head demagnetizer do not approach for the erase head.)
Do not use a magnetized screwdriver for the adjustments.
After the adjustments, apply suitable locking compound to the parts
adjusted.
The adjustments should be performed in the rated power supply
voltage unless otherwise noted.
Torque Measurement
Torque Torque meter Meter reading
ED CQ-102C © uase ozvinch)
oe €Q-102C 'as ere 'oztinch)
REV Co-102RC (049 t0 0.85 or neh)
Back tension Co OARS (0.05 16 0.68 ozvinch)
PRREW. CQ-201B 0 aay ssi)
3-2. ELECTRICAL ADJUSTMENTS
0dB 75 V (AF)
Precautions:
2.
3.
6.
Demagnetize the record/playback head with a head demagnetizer.
(Do not bring the head demagnetizer close to the erase head.)
Do not use a magnetized screwdriver fot the adjustments.
After the adjustments, apply suitable locking compound to the parts
adjusted
The adjustments should be performed with the rated power supply
voltage unless otherwise noted.
The adjustments should be performed in the order given in this
service manual. (As a general rule, playback circuit adjustment
should be completed before performing recording circuit adjustment.)
'The adjustments should be performed for both L-CH and R-CH.
© Switches and controls should be set as follows unless otherwise
specified.
DOLBY NR switch OFF
TAPE: TYPE!
Type Signal Used for
P-4-A100 6.3 kHz, — 10 dB Azimuth Adjustment
P-4-L300 315 Hz, 0 dB PB Level Adjustment
WS-48B 3 kHz, 0B Tape Speed Adjustment
Record/Playback Head Azimuth Adjustment |DECK A
Note: Perform this adjustments for both decks. DECK B
Procedure:
1. Mode: FWD playback
test tape
fio ket 202 1048) oscilloscope
L-CH
R-CH
CN504
within
1 dB
output
level 4
= Screw
position
L-CH R-CH
peak peak
'Screen pattern
QO@OQYD
in phase 45° 90° 135° 180°
——
wrong
good
3. After the adjustments, apply suitable locking compound to the parts
adjusted.
Adjustment Location:
= E25) 7 (=I
U
Adjustment screw
Rec/PB head (deck B)
or PB head (deck A)
DECK B
Tape Speed Adjustment [DECK A
Procedure:
Mode: playback
test tape
WS-48A
(3 kHz, 0 dB)
;
SE eI
CNS04 Pin
Pin
frequency counter
(L-CH)
(R-CH)
High speed adjustment
Short-circuit JWS and JW6 (main board) when the power is off.
'Tum on the power and put the deck A into the FWD mode.
Push HIGH SPEED button
Adjustment RV72 so that the frequency counter reads 6.000 + 60 Hz
'Adjust the deck B in the same manner as the deck B.
Remove the short of JWS and JW6.
SAY ®