Technics RS-273US - Page 7

‘TEM
MEASUREMENT & ADJUSTMENT
REMARKS
An example calculation is shown below.
A: Es=playback output signal voltage of test tape (333 Hz)
B: En=playback output noise level
Es=0.5 V (—6 dB)
En=3.5mvV (—49 dB)
: Es 0.5V
S/N ratio= = 35mV 141
20 log 10 141=43dB
or
S/N ratio=Es (dB) —En(dB) 6— (—49) =43dB
Bias Leak
Equipment :
* VTVM
* Oscilloscope
Bias Current
Equipment :
* VTVM
* Oscilloscope
1. Test equipment connection is shown below.
R25(L-CH)
R26 (R-CH)
TP4(R-CH)
(vIvM)
Fig. 14
2. Place unit into record mode.
3. Adjust trap coils L3 (L-CH), L4 (R-CH), so that measured
value become minimum.
. Take adjustment for both channels.
. Test equipment connection is shown below.
2. Place unit into record mode and tape selector to normal
position.
3. Read voltage on VTVM and caiculate bias current by fol-
lowing formula.
Value read on VTVM CV)
Bias Current (A) = TO (a)
Standard Value: 0.12+0.02mA
4. Adjust trimmer capacitors of VC1-1 (L-CH), and VC1-2 (R-
CH), if not in standard.
5. Then changing the tape selector to CrO2 position, confirm
that bias current become greater by 20% than that for
normal.
* Record Mode
* Record Level Control
... MAX
* Location of TP3, TP4, L3
and L4 are shown in fig.
26.
* Record Mode
* Be sure the ground end of
the meter is connected to
the nearest ground of
test point.
* When bias current Is
adjusted on one channel
only, note that bias
Current on the other
channel may vary.
* Location of TP1, TP2,
VC1-1 and VC1-2 are
shown in fig. 26.