Panasonic RS-612US-E - Page 12

11
Overall frequency response
(As a standard for adjustment)
MEASUREMENT & ADJUSTMENT
Adjustment — Using bias current
1. When the frequency response between the middle and high frequency
range becomes higher than the standard value, increase the bias current
by abe 3 (L-CH) or L4 (R-CH) in direction of counter-clockwise
(G).
_ When it becomes lower, reduce the bias current by turning in direction
of clockwise ( -) ).
REMARKS
Adjustment
Overall S/N ratio
Equipment:
* VTVM
* AF oscillator
* ATT
* Oscilloscope
* Test tape
(reference blank tape)
CRA
_ Test equipment connection is shown in fig. 15.
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
7.
Standard Value: Greater than 42dB
(without NAB filter)
Dolby NR circuit
Equipment:
* VTVM
* AF oscillator
* ATT
* Oscilloscope
Place UNIT into record mode, set the Dolby NR switch to OUT posi-
tion and supply to LINE IN to obtain —34.5dB at TP3 (L-CH), TP4
(R-CH) (frequency 5 kHz).
Confirm that the value at IN position is 7.5(+1.5)dB greater than
the value at OUT position of Dolby NR switch
* Record/playback mode
* Record level control
..- MAX
* Erase the tape with a
bulk tape eraser.
* Input selector---LINE IN
* Record mode
* Record level control
-» MAX
* Stop the bias oscillation
by unsoldering point (F)
see fig. 19 on page 12.