Operating instructions

6.2.2 Sync Amp Alignment
1. Engage the ALL SEL·REP button on the Remote Control Unit. ALL SAFE
should still be engaged.
2. Rewind the test tape and locate and play the 1 kHz reference tone.
3. The VU meters should indicate 0 VU. If any do not, adjust the SYNC
GAIN control on the corresponding AUDIO PCB Assembly as necessary
(Figure 6-13.)
4. Locate and play the 10 kHz tone on the alignment tape.
5. Adjust the SYNC HI SPD EQ or SYNC LOW SPD EQ on the AUDIO PCB
Assembly for each channel as required (depending on the tape speed
selected) to obtain a 0 VU indication for that channel.
6. Locate and play the 15 or 16 kHz reference tone. The VU meters should
be within 1.5 dB of 0 VU.
7. If a reproduce alignment tape is used for initial audio alignment, the
LOW FREQ COMP switch on the BIAS PCB Assembly should be in the
OFF position. If the machine is being aligned to setup tones recorded on
a session tape, turn the LOW FREQ COMP switch on the BIAS board to
the ON position and use the 100 Hz setup tone to adjust each AUDIO
PCB Assembly SYNC LOW FREQ EQ for the desired low frequency
response.
Figure 6-14
Sync Section of Audio PCB Assemblies
6.2.3 Bias Alignment
Three master bias controls are switch-selected so that once the individual
channels have been brought into proper bias balance, a single control can
reset the bias to accommodate up to three different tape formulations.
1. Extend the BIAS PCB Assembly (card #7 in the lower card cage).
2. Set the BIAS SELECT switch (SW1) to the 1 position.
3. With an oscilloscope connected to TP-1 on the BIAS PCB Assembly,
adjust VR1 (BIAS ADJ. 1) for 5 V P-P signal.
4. Thread a reel of blank tape on the machine.
5. Plug a test oscillator into the TEST SIGNAL jack on the front of the BIAS
PCB Assembly. This jack accepts a tip-sleeve 6.3 mm (1/4") phone plug.
6. Set the oscillator for +4 dBu output at 10 kHz.
7. On the Remote Control Unit, engage the ALL INPUT switch so the test
input signal can be monitored to check if it is present.
8. Now switch the Remote Control Unit to All Repro mode, disengage the
ALL SAFE button and set all READY/SAFE switches to READY position.
9. Press the RECORD and PLAY buttons to initiate recording of the 10 kHz
test signal.
REPRO
SYNC
GAIN
HI SPD
EQ
LOW SPD
EQ
LOW
FREQ
GAIN
REC
HI SPD
EQ
LOW SPD
EQ
LOW
FREQ
GAIN
MTR-90III Operation and Maintenance Manual
October 1990
Section 6 Alignment
6 - 21