Bias Setting Adjustment; Record Level; Overall Frequency Response - Tascam 122 Service Manual

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122
7-4. BIAS SETTING ADJUSTMENT
Before adjusting the bias setting :
a. Connect the measuring instruments as shown
in Fig. 7-3.
b. Load a blank tape and put the deck in the
record/pause mode.
c. Apply a -14 dBV/400 Hz signal to the LINE
1 or 2 terminal.
d. Adjust the INPUT (LEFT/RIGHT) level con ­
trol until the VU meter reads 0 VU.
e. Adjust the OUTPUT level control so that the
OUTPUT terminal level is -10 dBV.
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Fig. 7-3
Bias setting at position METAL
1) Set the EO and B I AS switches to META
L.
2) Al,ternately record -44 dBV signals at 400 Hz
then 10 kHz on blank tape (MTT-5072) and
reproduce them.
NOTE: The level -44 dBV is 30 dB lower than
the standard level.
3) Note readings of the OUTPUT lev'el at the
OUTPUT terminal and
che~k
that the output
levels are identical for both frequencies.
4) If the resul,t is unsatisfactory, adjust semi­
fixed resistors R 15/R25.
NOTE: Turning the semi-fixed resistors clock­
wise increases bias current and decreases
high frequency response; turning them
counterclockwise increases high fre ­
quency response.
Bias settings at NORMAL and Co (Cr02)
positions
This is done in the same way as for the metal
bias setting. Refer to the following table :
Blank tape Adjusting points
Positions EO/BIAS switches
L
R15/R25 METAL
MTT·5072
ilBIAS METAL
R l4/R24
MIT·5061 Co(CrOz)
I ~IAS
Co(CrOz)
NORMAL MIT·501 R13/R23 BIAS N 'ORMAL
48
7-5. RECORD LEVEL
Adjust this after the setting of the reproduce
and b ias levels (7-1 and 7-4) and VU meter (7-2)
is complete.
The following items 1) - 5) indicate the
standards levels and setting orders of each
control.
METAL
1) Connect the measuring instruments as shown
in Fig. 7-3.
2) Set the BIAS and EO switches to METAL and
the MONITOR switch to SOURCE.
3) Load blank tape (MTI-5072) and set the deck
in the record/pause mode.
4) Apply -14 dBV/400 Hz signals to LINE 1 or
2 .
5) Adjust the INPUT (LEFT/RIGHT) level con ­
trol until the VU meter reads 0 VU . Adjust
the OUTPUT level control so that the OUT­
PUT terminal level is set to -10 dBV.
6) Set the MONITOR switch to TAPE. Record
and play the blank tape to check that the
OUTPUT level is -10 dBV
±
1 dB.
7) If satisfactory values are not obtained, adjust
semi-fixed resistors R 16/R26.
Co(Cr02) and NORMAL
This is done in the same way for metal tape.
Perform adjustment referring to the following
table.
Positions EO/BIAS switches Blank tapes Adjusting po ints
METAL METAL MTT·5072 R16/R26
Co(CrO z) Co(CrOz)
MIT·5061
R17/R27
NORMAL NORMAL
MTT-50l R18/R28
7-6. OVERALL FREQUENCY RESPONSE
METAL
Obtain the standard setting according to proce ­
dures 1) - 6) of 7-5. and ch eck the record/
reproduce sigr.als.
1) Obtain -44 dBV by decreasing the input
signal level by 30 dB and record and play it
on blank tape (MTT-5072).
Change the input signal level and confirm that
the level at 12 kHz is within ±2 dB of the level
at 400 Hz. Also confirm at high tape speed.
I f the response is unsatisfactory, check
whether the record/reproduce head is - d irty or
set correctly. It is also necessary to check the
bias level setting.
NOTE: Perform this adjustment with the N R
SYSTEM switch set OUT.