JVC MX-GT91R Service Manual page 29

Electrical performance
Items Measurement
conditions
Adjustment of
*Mode : Forward or
recording bias
reverse mode
current
*Recording mode
(Reference
*Test tape
value)
: AC-225
Measurement output
terminal
:Both recording and
headphone terminals
Adjustment of
Reference frequency
recording and
:1kHz and 10kHz
playback
(REF:-20dB)
frequency
Test tape
characteristics
:TYP AC-225
Measurement input
terminal
:OSC IN
Reference values for electrical function confirmation items
Items Measurement
conditions
Recording
*Recording and
bias frequency
playback side forward
or reverse
*Test tape
:TYP AC-225
*Measurement
terminal BIAS TP on
P.C.board
Eraser current
*Recording and
(Reference
playback side forward
value)
or reverse
*Recording mode
*Test tape
:AC-225
Measurement terminal
Both of the eraser
head
Measurement method
1.With the recording and playback mechanism,
load the test tapes(AC-225 to TYP ),and set the
mechanism to the recording and
pausing conditions in advance.
2.After connecting 100 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 ).
1.With the recording and playback mechanism,load
the test tape(AC-225 to TYP ),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 ),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 ),and set the
mechanism to the recording and pausing condition
in advance.
2.After setting to the recording conditions,connect
1M in series to the eraser head on the recording
and playback mechanism side,and measure the
eraser current from both of the eraser terminal.
MX-GT91R
Adjusting
Standard
positions
values
AC-225
LcH
:4.20 A
:VR101
RcH
:VR201
Output
LcH
deviation
:VR101
between
RcH
1kHz and
:VR201
10kH
:-1dB 2dB
Adjusting
Standard
positions
values
100kHz
+9kHz
-7kHz
TYP
:75mA
1-29