JVC MX-GA9V Service Manual page 39

4.6 Electrical performance
Items Measurement conditions
Adjustment of *Mode : Forward or reverse mode
recording *Recording mode
bias current *Test tape : AC-225
(Reference Measurement output terminal
value) : Both recording and headphone
terminals
Adjustment of Reference frequency : 1kHz and
recording and 10kHz (REF : -20dB)
playback Test tape : TYP l AC-225
frequency Measurement input terminal : OSC IN
characteristics
4.7 Reference values for electrical function confirmation items
Items Measurement conditions
Recording *Recording and playback side
bias forward or reverse
frequency *Test tape : TYP l AC-225
*Measurement terminal BIAS TP on
P.C.board
Eraser *Recording and playback side
current forward or reverse
(Reference *Recording mode
value) *Test tape : AC-225
Measurement terminal Both of the
eraser head
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Measurement method
1.With the recording and playback
mechanism, load the test tapes(AC-225
to TYPl),and set the mechanism to the
recording and pausing conditions in
advance.
2.After connecting 100Ω in series to the
recorder head,measure the bias current
with a valve voltmeter at both of the
terminals.
3.After resetting the [PAUSE] mode,start
recording.
At this time,adjust VR101 for LcH and
VR201 for RcH so that the recording bias
current values become 4.0 A (TYP l).
1.With the recording and playback
mechanism,load the test tape(AC-225
to TYP l), and set the mechanism to the
recording and pausing condition in
advance.
2.While repetitively inputting the
reference frequency signal of 1kHz and
10kHz from OSC IN, record and
playback the test tape.
3.While recording and playing back the
test tape in TYP, adjust VR101 for LcH
and VR201 for RcH so that the output
deviation between 1kHz and 10kHz
becomes -1dB ±2dB.
Measurement method
1.While changing over to and from
BIAS 1 and 2, confirm that the
frequency is changed.
2.With the recording and playback
mechanism, load the test tape (AC-225
to TYP l), and set the mechanism to the
recording and pausing conditions in
advance.
3.Confirm that the BIAS TP frequency
on the P.C.board is 100kHz ±6kHz.
1.With the recording and playback
mechanism, load the test tapes (AC-
225 to TYP l), and set the mechanism
to the recording and pausing condition
in advance.
2.After setting to the recording
conditions,connect 1MΩ in series to
the eraser head on the recording and
playback mechanism side,and
measure the eraser current from both
of the eraser terminal.
Standard values Adjusting positions
AC-225 : 4.20µA LcH : VR101
RcH : VR201
Output deviation LcH : VR101
between 1kHz RcH : VR201
and 10kH
: -1dB ±2dB
Standard values Adjusting positions
100kHz
+9kHz
-7kHz
TYP : 75mA
(No.MB011)1-39