Panasonic RS-612US-E - Page 9

MEASUREMENT & ADJUSTMENT
An exampie calculation is shown below.
A: Es = playback output signal voltage of test tape (333Hz)
B: En=playback output noise level
Es =0.42V (—7dB)
En=2.1mV (—53 dB)
. Es 0.42V
S/N ratio = En = 3 OmV = 200
20 logio 200 = 46dB
S/N ratio = Es(dB) — En(dB) = —7 —(—53) =46dB
REMARKS
Bias current
Equipment:
*VTVM
* Oscilloscope
1. Test equipment connection is shown below
TPL{L-CH)
TP2{R-CH)
Record mode
R5(L-CH)
R6(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)
10 (Q)
Bias current (A) =
rl
Standard value:
! 500! fea%A (LOW position) |
600 + 290#A
—150uA (HIGH position)
4. Adjust L3 (L-CH) and L4 (R-CH) (See adjustment part location on
page 12)
5. Then changing the bias selector to “HIGH”, confirm that bias current
become greater by 25% than that for normal.
* 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 L3 or L4 is the
replaced, preset core
position to bottom side of
coil and then readjust
optimum bias current.
Erase current
Equipment:
*VTVM
* Oscilloscope
* Resistor (0.19)
|
1
1. Connect 0.12 resistor between ground side terminal of erase head
ground lead wire removed (See fig. 14).
2. Connect VTVM to both ends of 0.1 resistor
Erase head
Record mode
VTVM Oscilloscope
Fig. 13
3. Place UNIT into record mode, and measure voltage across the 0.122
resistor.
4. Determine erase current with the following formula:
Erase current (A) =
| Standard value: |
100£40mA (LOW position)
| 120450 mA (HIGH position)
+ Record mode
Erase head
Fig. 14