Revox A77

6.4. Oscillator and RF - Adjustments
6.4.1. RF - Voltages and Frequency Checking
— Set controls per fig. 6.4 — 59
C NNNNNN
MONITOR
NIN
Fig. 6.4-59
RECORD
— Load tape and switch to RECORD ( STEREO ).
A. — Measure erase head voltage against ground with VTVM
at VU- meter board ( fig. 6.4 — 60 ) orange HB3 ( CH 2 ) and
blue HB6 ( CH 1 ).
2 - Track = 21 Vac each
4 - Track = 16 Vac each
blu HB6
org HB3
Fig. 6.4-60
6
3
B. Oscillator Frequency
— Load tape, switch to RECORD ( STEREO ). Pull out
lamp at optical end- of- tape switch if measuring without
tape.
— Oscillator frequency is measured with digital counter or
oscilloscope. The frequency is 120 kHz ( ± 5 kHz ) and
is measured at orange HB3 and blue HB6 ( fig. 6.4 — 60 )
against ground. ( Oscilloscope: 12 oscillations per 100
µsec ).
6.4.2. Dummy Load
The dummy load compensation is needed only when the
erase head is replaced ( balance of inductive strays from the
erase head during MONO - operation ).
— Load tape, switch to RECORD.
— Connect digital counter or oscilloscope to blue HB6
( fig. 6.4 — 60 ).
CRANNM.
_A
— Measure RF - frequency in stereo mode.
— Disengage record pre- selector CH 2 and balance DUMMY
LOAD till same frequency is reached as in stereo mode.
REPR ltVEt
o
REImO.CE ANI•os« • 0.2
MRS MAP
Fig. 6.4-61
o
MOM)
C112
- 0
EIYMDI
".
LEVEL
OfOLLATOR
s, 0
CIO
-0
- 0
RECORO
, MR/M1 0... y
— Depress record pre- selector CH 2 and disengage CH 1.
Connect oscilloscope or digital counter to orange HB3.
— Correct DUMMY LOAD if necessary.
CfmNNEL
— Repeat adjustment procedure until any remaining fre-
quency deviations are symmetrical around the nominal
frequency ( e.g. CH 1 + 1 kHz, CH 2 - 1 kHz ).
6.4.3. RF - Traps, Record
— Set controls per fig. 6.4 — 62
MONITOR
Fig. 6.4-62
CRPNRill. II
RECORD
— Load tape, switch to RECORD ( STEREO ).
— Connect VTVM to test point C 515 of the respective
record amplifier ( fig. 6.4 — 63 ), see also diagram 1.077.
705.
C515
Record Amplifier 1.077.705
Fig. 6.4.-63
Il
- t
z
28