Panasonic RS-612US-D - Recording Performance Measurements

Bias current
Equipment:
* VTVM
* Oscilloscope
——_—___—_}-__-_——
MEASUREMENT & ADJUSTMENT
An example calculation is shown below.
A: Es = playback output signal voltage of test tape (333 Hz)
B: En=playback output noise level
Es =0.42V (—7dB)
En=2.1 mV (—53 dB)
F Es 0.42V
S/N ratio ==, = 30mv = 200
20 logio 200 = 46dB
S/N ratio = Es(dB) — En(dB) = —7 —(—53) = 46 dB
1. Test equipment connection is shown below.
TPII(L-CH)
TP2(R-CH)
VTVM Oscilloscope
Fig. 12
2. Place UNIT into record mode, and bias selector to “LOW”.
3. Read voltage on VTVM and calculate bias current by following for-
mula:
Value read on VTVM (V)
Bias current (A) = 10 ©)
Standard value:
500+ 72 5Mq (LOW position)
+250uA 7
| 600 7 150A (HIGH position) |
. Adjust L3 (L-CH) and L4 (R-CH) (See adjustment part location on
page 12).
. Then changing the bias selector to “HIGH”, confirm that bias current
become greater by 25% than that for normal.
Erase current
Equipment:
* VTVM
* Oscilloscope
* Resistor (0.12)
REMARKS
* Record mode
* Be sure the ground end of
the meter is connected to
the ground end of the
resistor.
* When bias current is the
adjusted on one channel
only, note that bias current
on the other channel may
vary.
* When L.3 or L4 is the
replaced, preset core
position to bottom side of
coll and then readjust
optimum bias current.
. Connect 0.12 resistor between ground side terminal of erase head
ground lead wire removed (See fig. 14).
. Connect VTVM to both ends of 0.1 resistor.
Erase head
O
Fig. 13 VTVM Oscilloscope
3. Place UNIT into record mode, and measure voltage across the 0.12
resistor.
4. Determine erase current with the following formula:
_Voitage across both ends of 0.12
0.12 ~ ~
Erase current (A) =
| Standard value:
100+40mA (LOW position)
120+50mA (HIGH position)
* Record mode
Erase head