Record/Reproduce Amplifier Checks And; Reproduce Output Level Setting; Vu Meter Setting; Reproduce Frequency Response - Tascam 122 Service Manual

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7. RECORD/REPRODUCE AMPLIFIER CHECKS AND ADJUSTMENTS
Remove the top cover by unscrewing the scrElWS
securing it. When the top cover is removed, the
record/reproduce amplifier PCB ASSY can be
seen. When adjusting the azimuth of the record/
reproduce head, remove the cassette holder door
cover.
The following points should be observed before
starting the record/reproduce amplifier checks
or adjustments.
*
Before adjusting the amplifier, the erase head,
record/reproduce head and tape path shou I d
be demagnetized and cleaned with cleaning
fluid.
*
Adjust the left channel first, then the right
channel. In the circuit diagrams, 100-series
numbers refer to left channel components and
200-series numbers refer to right channel
components. For example, R180 is a left
channel resistor while R280 is the equivalent
right channel resistor.
Left channel/Right channel components are
shown as R180/R280.
*
0 dB
=
1 V
*
Unless otherwise specified, set the switches as
follows:
Switches Positions
MONITOR
TAPE
DDLBY NR OUT
INPUT
LlNElor2
SPEED STANDARD
EQ
METAL
BIAS METAL
MEMORY
OFF
CAL
PRESET
* If characteristics such as frequency response
and crosstalk are found to be unsatisfactory,
it is necessary to check and adjust the
azimuth of the record/reproduce head first
prior to performing amplifier adjustment.
. Record/reproduce head azimuth check and
adjustment
Connect an oscilloscope and a VTVM to the
OUTPUT terminals as shown in Fig. 7-1. Play
test tape MTT-150 to check that the phase dif­
ference between the Land R channels is less
than 45°.
Reproduce the 10-kHz/-10dB signal from test
tape MTT-316 and turn the azimuth adjusting
nut to maximize the levels of both channels.
OSCILLOSCOPE
O ~
VER HOR
AMP SPKR
AC VOLTMETER
EJ
0 0
UNIT
under TEST
F OU~TF'VT==t~o-1
I-­
Fig. 7-1
0 ° (IN PHASE)
Fig. 7-2
7-1. REPRODUCE OUTPUT LEVEL
SETTING
1) Load test tape MTT-150 and play it.
2) Connect the HOT terminal of the VTVM to
DOLBY T .P. (TP.1/TP.2) and the COLD
terminal of the VTVM to TP (GND) and
check that the DOLBY T.P. voltage is 580 mV
(-2.5 dB).
3) If this value cannot be obtained, adjust
sem i-fixed resistors R 11 /R21.
4) Also connect the VTVM to the OUTPUT
terminal and confirm that the OUTPUT level
is -4.5 d-BV ±2 dB when the OUTPUT level
control is max imum.
7-2. VU METER SETTING
1) Load test tape MTT-150 and play it.
2) Check that the VU meter reading is +3 VU ± 1
VU.
3) If the VU meter reading is not correct, adjust
semi-fixed resistors R71/R81.
7-3. REPRODUCE FREQUENCY RESPONSE
1) Connect a VTVM to the OUTPUT term ina!.
2) Play test tape MTT-316 and check the output
level. Confirm that the level at 10kHz is
within ±2 dB of the level at 315 Hz.
3) If the response is unsatisfactory, adjust semi­
fixed resistors R 1 O/R 20. I f the resu It is sti II
unsatisfactory, check the tape travel and head
azimuth.
4) Play the 10-kHz signal from the test tape and
change the EQ switch setting to NO RMAL.
Confirm that the output level is about 4.5 dB
~~
higher than with the switch in the METAL
position.
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