Sanyo MR-939 - Page 3

HEAD ADJUSTMENTS
Relative Position of Heads and Tape (refer to fig. 5)
Thread the recorder with tape and set in Playback mode.
Pull back the tape pads and adjust the relative position of the
heads and tape (see fig. 5) by turning the adjustment screws
for each head. The erass head does not require precise azimuth
positioning.
Record/Playback Head
Connect a VTVM to one speaker jack and play a 4-track
standard alignment tape (7000 c/s). Turn the adjustment screws
until maximum meter reading is obtained. Check the other
channel for a similar meter reading and readjust the first
channel slightly if necessary to obtain equal output.
ELECTRICAL ADJUSTMENTS
Bias Oscillator Frequency (fig. 7).
) MODEL “939”
OSCILLOSCOPE
Record
Mode
AF
Oscillator.
R-52
or R-152
Fig. 7
Connect a 10 ohm resistor (R52 or R-152) in series with the
ground lead wire of the Record/Playback head as shown in
Fig. 7.
Connect the vertical input of an Oscilloscope across a resistor;
connect the horizontal input of the Oscilloscope to the output
terminal of the audio frequency oscillator (A.F. Oscillator).
When the unit is set in Record mode and connected as above,
a lissajous figure will appear on the oscilloscope.
Standard frequency is 80Kc +5 Ke.
It is only necessary to measure one channel. If the frequency
is not within the above range, change the oscillator coil or
) C-206 (0.002“F).
MAINTENANCE
Oiling and Cleaning
All rotating parts of this set are permanently lubricated.
To ensure smooth functioning, oil-less metal parts are sealed
from exposure to air. Accordingly, these parts must be dis-
assembled before reapplying lubricant. This tape recorder does
not as a rule require oiling, however, it is preferable to oil
once year or when parts are repaired, as follows:
Pressure Roller 1 drop
Flywheel Shaft 2 drops
Rewind Roller 1 drop
Motor Shaft 2 drops
Reel Base and Reel Base Pulley 1 drop
Counter and Shaft 1 drop
Rewind Idler 1 drop
If excessive oil is applied it may overfiow along the shaft
and adhere to the rubber parts of the belt and pressure roller,
causing slipping, wow or flutter.
Care should be taken to limit the amount of oil applied.
Recording Level
Terminal
MIC.
MODEL
ATTENUATOR | “939”
gn
(=1] Volt Constant)
Fig. 6
Connect as shown in fig. 6.
Connect the attenuator to the recorder Aux. input then con-
nect the recorder speaker jacks to the VIT'VM via a parallel
resistor (8 ohms). Set in Record mode and turn the volume
control to maximum and the tone control to the monitor position
until a click is heard.
Adjust the AF oscillator to produce 1 volt at 1000c/s on the
VTVM, and regulate the attenuator output for —66 dB at 1000c/s.
This signal is fed into the microphone jack of the recorder.
Adjust VR-1 & VR-101 to read 0.8 V on the VITVM.
The VU meter is then calibrated at 0-VU for this output level.
Adjustment of VU meter is done using SVR-2 and SVR-102.
Bias Current (Fig. 8)
R/P Head
AC VTVM
MODEL “939”
Proper bias is necessary for optimum recording. Adjust the
bias oscillator frequency as described before. Bias current
during the recording is measured at both ends of R52 (CH-1)
or R152 (CH-2). Adjustment is made by a semifixed CT-1,
CT-101 so the voltage will be 2mV on an AC VTVM. Recording
bias current is 0.9mA (voltage across the 10 ohm resistor ;
0.9 mA x 10-3 x 10 = 0.009 V).
Cleaning the Tape Transport Sections
The tape travels from the feed reel to the pinch roller through
two tape guides, an erasing head, a recording head, pad, tape
guide and capstan.
When dust or ferrous powder on the tape adheres to these
parts, insufficient erasing, non-recording, poor high tones, re-
duced volume and slipping may result, so the utmost care should
be taken when cleaning these parts.
Parts such as the tape guides, each head, the pinch roller
and capstan should be thoroughly cleaned with a soft cloth or
gauze moistened in alcohol or head cleaning solution.
Head De-Magnetization
Magnetization of the heads may result when the continuity
of the heads is measured with an ohm meter. If it is necessary
to measure head continuity, the heads should be de-magnetized
after continuity check.
A magnetized head can be neutralized with the use of a
standard de-magnetization tool. The tip of the tool should not
be used through the pad, but should be thin enough to fit
between the pressure pad and the head. A piece of cellulose
tape should be placed over the head of the tool to prevent
metal to metal contact between the tool and the head.
After de-magnetization, slowly remove the tool from the
vicinity of the head before turning off the current.