Technics RS-646DS-D

ITEM
MEASUREMENT & ADJUSTMENT
Note:
1.
For adjustment when the bias current is lower than the standard value
0.29mA, the bias current beyond this point may worsen the distortion
factor.
For the method of bias current measurement, refer to “Bias current
adjustment” on page 10.
REMARKS
Overall S/N ratio
Equipment:
* VTVM
* AF oscillator
+ ATT
* Oscilloscope
* Test tape---C-RA
(reference blank tape)
. Test equipment connection is shown in fig. 19.
. Supply 1kHz signal to LINE IN and adjust ATT so that output level
at LINE OUT indicates 0.42 V (—7 dB).
. Make recording.
Make another recording without supplying signal (disconnect input
plug to LINE IN).
Rewind to recorded part and playback.
Measure output signal 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
9.
Standard value: Greater than 40dB
(without NAB filter)
ij
* Record/playback mode
* LINE IN level control
ve MAX
* Erase the tape with a bulk
tape eraser.
| * Bias selector ----+-++- LOW
* EQ selector
Dolby NR circuit
Equipment:
* VTVM
* AF oscillator
* ATT
* Oscilloscope
DaRw
N
Place UNIT into record mode, set the Dolby NR switch to OUT posi-
tion and supply to LINE IN to obtain —34.5dB at TP1(L-CH), TP2
(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 VR3 (L-CH), VR4 (R-CH) to maximum.
Set the Dolby NR switch to IN position.
At this time adjust VR5 (L-CH), VR6 (R-CH) so that the reading of
VTVM become 10dB greater than the value in step (1) above.
Adjusting VR3 (L-CH), VR4 (R-CH), make the reading of VTVM be-
come 2dB smaller than the value obtainted through the adjustment
in step (6) above. (See adjustment parts location on page 17).
* Record mode
* LINE IN level control
..» MAX
* Stop the bias oscillation by
unsoldering point L302
shown in circuit board
on page 20
14