Fostex A-8 - 6. Special Maintenance (A-8 LR); Amplifier Calibration and Adjustments

6. SPECIAL MAINTENANCE
6.4 RECORD/REPRODUCE AMPLIFIER CHECKS AND ADJUSTMENTS
Checking and adjusting of the record/reproduce amplifiers can speedily and
efficiently be carried out by following the procedures below.
Model A-8LR, R/P amp card installation.
Plate, PCB locking
CH-8
CH-7
CH-6
CH-5
6.4.1 Calibrating the Dolby encode mode and meters
1) Put transport in the EDIT mode. To calibrate TRACK 1, depress the RECORD
TRACK 1 button, simultaneously depress RECORD and PLAY buttons to put TRACK 1
(CHAN. 1) in the record mode.
2) Plug in an audio oscillator output to the recorder rear panel INPUT 1 jack
and apply a 400Hz, -lOdBV (0.3V) signal.
3) Set the NR INT/EXT switch on the recorder front panel to EXT, connect a level
meter to test point TP-101 and adjust REC CAL (R-311, IOKQ b ) so that the
level here is 390mV.
4) On c rwn plgj-ing the above adjustments, connect the level meter to OUTPUT 1 jack
on the recorder rear panel and check that the level here is — lOdBV (0. 3V) ±ldB .
5) After checking the OUTPUT jack level, adjust METER CAL (R-312, 50K2B) for a
0 VU reading on the recorder VU meter.
6) Calibrate tracks 2 8 in the same way.
7) Return the NR INT/EXT switch, on the recorder front panel, to INT.
6.4.2 Calibrating the Dolby decode mode
1) Set the NR INT/EXT switch on the recorder front panel to EXT and switch off
all RECORD TRACK buttons.
2) Playback the Reference Level Section of the Reproduce Alignment Tape.
3) Beginning adjustments from TRACK 1 (CHAN 1), connect a level meter to test
point TP- 101 located near U106 upon the CHAN 1 PCB of the record/reproduce
amplifier, and adjust REP CAL (R314, lOKflB) so that the level is 390mV.
4) After these adjustments, connect the level meter to the recorder rear panel
OUTPUT 1 jack and check that the level is -lOdBV (0.3V) ±ldB.
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