Technics RS-676US - Dolby NR and FM Circuit Adjustments

MEASUREMENT & ADJUSTMENT
REMARKS
Overall S/N Ratio
Equipments:
* VTVM
* AF Oscillator:
* ATT
* Oscilloscope
* Test Tape (Reference
Blank Tape)...C-RA
. Test equipments connection is shown in fig. 23. :
2. Supply 1kHz signal (—14 dB), and adjust record level
contro! so that VU meter indicates 0 VU.
. Further adjusting ATT, increase input signal by 4 dB. (Line
output level: 0.42 V (—7 dB) +4 dB=0.7 V (—3 aB))
. Make recording.
. Make another recording without supplying signal (discon-
nect input plug from LINE IN).
. Rewind to recorded part and playback.
. Measure output signa! level and no signal level (noise),
and determine the ratio in decibels (dB).
. The value is difference between “playback S/N and overall
S/N”, but for decibel calculation refer to “Playback S/N
measurement” on page 11.
Standard Value: Greater than 47 dB
(without NAB filter)
* Record/Playback Mode
* Record Level Control
.-MAX
* Erase the tape with a bulk
tape eraser.
Dolby NR Circuit
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
Dolby FM
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
. Place UNIT into record mode, set the Dolby NR switch to
OUT position and supply to LINE IN to obtain —34.5 dB at
TP3 (L-CH), TP4.(R-CH) (frequency 5 kHz).
. Confirm that the value at IN position is 8dB greater than
the value at OUT position of Dolby NR switch.
. When it is not in condition above, adjust as follows.
. Set VR401. (L-CH), VR402 (R-CH) to maximum.
. Set the Dolby NR switch to IN position.
. At this time adjust VR403 (L-CH), VR404 (R-CH) so that
the reading of VTVM become 10dB greater than the value
in step (1) above.
. Adjusting VR401 (L-CH), VR402 (R-CH), make the reading
of VTVM become 2dB smaller than the value obtained
through the adjustment in step (6) above.
. Test equipments connection is shown in fig. 22.
. Place UNIT into record mode:
. Set the Dolby FM switch to IN position and FM CAL VR,
VR21 (L-CH), VR22 (R-CH) to maximum.
. Supply 5kHz signal, and adjust ATT so that output level
at LINE OUT becomes 580 mv.
. Supply 5kHz signal (22dB smaller than the input level
above) to tuner input jack (selector switch: tuner).
. Confirm that the value at IN position is 8dB greater than
OUT position of Dolby NR switch.
+ Record Mode *%
* Record Level Control
..MAX.
* Stop the bias oscillation
by unsoldering a wire (C)
shown in adjustment
parts location on page
19.
* Record Mode
* Dolby FM Switch...IN
* De-Emphasis Switch
...Conventional Position
De-Emphasis Charactaristic
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
. Test equipments connection is as same as above.
. Place UNIT into record mode.
. Set the Dolby FM switch to IN position and FM CAL VR21
(L-CH), VR22 (R-CH) to maximum.
. Set De- Emphasis switch to 75s position.
. Supply 100 Hz signal, to TUNER IN and adjust ATT so that
output level at LINE OUT becomes 58 mV. (selector switch:
TUNER)
. Change De-Emphasis switch to 25us position and confirm
that the value at LINE OUT is 3dB+1 greater than the
value for 75us position.
* Record Mode
* Source Selector... Tuner