Technics RS-646DS-D - Page 11

Bias current
Equipment :
*VTVM
* Oscilloscope
Erase current
Equipment:
* VTVM
* Oscilloscope
* Resistor (12)
MEASUREMENT & ADJUSTMENT
1. Test equipment connection is shown below.
Record mode
R7{L-CH)
VIVM Oscilloscope
Fig. 16
2. Place UNIT into record mode, and bias selector switch to "LOW",
position.
3. Read voltage on VTVM and calculate bias current by following for-
mula:
Value read on VTVM (V)
Bias current (A) = 10 @)
Standard value: 0.3+0.001mA
. Adjust L.5 (L-CH) and L6 (R-CH) (See adjustment part location on
page 17).
. Then changing the bias selector to “HIGH”, confirm that bias current
become greater by 30% than that for normal.
. Connect 12 resistor between ground side terminal of the erase head
ground lead wire removed (See fig. 18).
. Connect VTVM to both ends of 1 resistor.
Erase head
o
VTVM Oscilloscope
Fig. 17
3. Place UNIT into record mode, and measure voltage across the on
resistor.
4. Determine erase current with the following formula:
Voltage across both ends of 1 (Q)
1 (Q)
Erase current (A) =
Standard value:
Bias LOW: 90+20mA
Bias HIGH: 120+30mA
REMARKS
* Record mode
* Be sure the ground end of
the meter is connected to
the ground end of the
resistor.
* When bias current is
adjusted on one channel
only, note that bias current
on the other channel may
vary.
* Record mode
Erase head
BLACK
Fig. 18
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