Operating instructions

7. All the VU meters should now indicate 0 VU. If any do not, adjust the
RECORD GAIN control on the corresponding AUDIO PCB Assembly as
required (Figure 6-15).
8. Switch the test or console oscillator to provide a 10 kHz signal at 0 VU to
the inputs.
9. All the VU meters should now indicate 0 VU. If any do not, adjust the
RECORD HI SPD EQ (or RECORD LOW SPD EQ) as required to obtain a
0 VU indication for that channel.
10. Switch the oscillator to 15 kHz at 0 VU level. The VU meters should be
within 1 dB of 0 VU.
11. Switch the oscillator to 1 Khz at 0 VU level and confirm that the record
level is still 0 VU. If necessary, repeat Steps 7-10.
12. Push the STOP button and engage the ALL INPUT button on the Remote
Control Unit.
13. Apply the 1 kHz, 0 VU signal from the oscillator or the console again.
14. Adjust the MONI (monitor) control on each AUDIO PCB Assembly to
obtain a 0 VU meter indication. This matches the input sensitivity and
monitor level of the MTR-90III to the output level of the mixing console.
6.2.5 Record Phase Compensation
Adjustable record phase compensation networks are provided for the record
amplifier circuitry. These networks enable the circuit to be optimally
compensated for group delay introduced by the record equalization circuitry
with separate adjustments for both operating speeds. The result is superior
transient and square wave response as well as higher recording level
capability with complex waveforms before saturation occurs.
The following procedure assumes that the bias, level, and equalization have
been calibrated according to the above instructions and that LF COMP on the
BIAS CONTROL PCB Assembly is switched off.
1. Connect an oscilloscope to the LINE OUTPUT of one track.
2. Apply a square wave of 1 kHz (5 kHz if available ) at 0 VU for 15 ips or
10 kHz at 0 VU for 30 ips to the inputs.
3. Switching the Output Monitor selector between REPRO and INPUT (or
SEL·REP), adjust the LOW PHASE control or the HI PHASE control
(depending upon the tape speed selected) on the AUDIO PCB Assembly
being monitored until the repro signal is most similar to the input signal.
Refer to Figure 6-16.
AUDIO
REC
LOW
FREQ
GAIN
BIAS
PHASE
EQ
PHASE
HI SPD
PHASE
EQ
LOW SPD
GOOD
WRONG
(UNDER COMP.)
WRONG
(OVER COMP.)
MUST BE FLAT
Figure 6-16
Record Section of Audio PCB Assemblies
AUDIO
REC
GAIN
BIAS
PHASE
EQ
PHASE
HI SPD
PHASE
EQ
LOW SPD
Figure 6-17
Phase Compensation Adjustments
MTR-90III Operation and Maintenance Manual
October 1990
Section 6 Alignment
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