Dual C 839 RC Service Manual page 7

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Alignment instructions motor electronic system
Test instruments and test cassettes required
1 vvovv meter
1 tape tension test cassette (KDW 231, item no. 232 797)
1 tape speed test cassette 3150 Hz
Take-up friction and tape speed
All trimmers set to centre position or pre-aligned.
Servicing plug in position "N" (normal mode)
Pitch control set to centre position (engaged)
Insert Sony TOR QUE METER cassette
Set tape tension to 50 ± 5 pcm with R 4524
4
Tape tension must lie between 45 and 65 pcm.
Insert Dual cassette 3150 Hz.
Set tape speed to ± 0.5% with R 4505.
Wow less than <0.1 %.
4
Tape speed must be within the tolerance range of ±0.5 %
Wow less than <0.1 %.
Servicing plug in position "S" (servicing).
Set tape speed to ± 0.5 % with R 4503.
Wow less than <0.1 %.
4
Tape speed must lie within the tolerance range of ± 0.5 %.
Wow less than <0.1 %.
Servicing plug "N" (normal)
Alignment instructions analog section
Test instruments and test cassette required
2 millivoltmeters
1 AF oscillator
1 oscilloscope
1 frequency counter
1 test cassette 400 Hz —20 dB, 10 kHz —20 dB
1 test cassette Fe203 reference medium section, Cr02 reference
medium section
1 test cassette 400 Hz Dolby level 200 nWb/m
General notes
Before alignment, the magnetic head and all ferrous components
contacting the tape must be demagnetised!
Realignment must be carried out in the sequence stated.
When aligning the coils, two core positions are possible. Howe-
ver, the outer core position should always be chosen.
Caution: the adjustment controls for the LED display must not
be altered.
Playback
Level and LED modulation display
Set R 4035 and 4035' to fully counterclockwise position (when
viewed from the front).
Apply the Dolby reference level (400 Hz).
Fe, 1>
Set a playback level of 580 mV ± 0.25 dB while the Dolby refe-
rence signal tape is running, measured at MP 3 (left channel) and
MP 3' (right channel)
Set track 1 lieft channel) with R 4054
Set track 2 (right channel) with R 4054'
Set track 3 (left channel) with R 4052
Set treck 4 (right channel) with R 4052'
Set the LED modulation displays to 0 dB while the Dolby refe-
rence signal tape is running.
For the left LED display, use R 4127
For the right LED display, use R 4127'
Magnetic head adjustment
Insert the test cassette section determined for gap adjustment
(noise or 10 kHz).
Fe, 1> (track 1-2) or 4 (treck 3-41
With the set screw at the left, adjacent to the magnetic head,
align for maximum voltage. Average the voltage at outputs L
and R or switch both channels in parallel and align to maximum.
Average the setting for both tape directions.
Frequency response
Insert the test cassette, section for determining frequency res-
ponse (400 Hz —20 dB — 10 kHz —20 dB).
Fe, (track 1-2) or 4 (track 3-4)
The output voltage at output L/R should be 0 dB with reference
to 400 Hz.
With reference to 10 kHz = +4t0 —3 dB
Deviations between channels at 10 kHz less than <3 dB.
When switching over to Cr02 or FeCr, the 10 kHz level must be
characterised by a voltage jump of —4 dB ± 1 dB.
Background noise
Screened amplifier, ensure that the magnetic head is free of hum.
Insert the wow test cassette.
PAUSE, DOLBY,
or 4
Background noise at OUTPUT L/R less than <2 mV rms, mea-
sured with 10w-pass filter 20 Hz — 3 dB
RF generator
Preset R 4084, R 4084', R 4082 and R 4082' for RF biasing or
set to centre position.
Measure the generator frequency with an absorption frequency
meter near the erase head or with a frequency counter at the
erase head via a 1 MSZ series resistor.
Set 105 kHz ± 2 kHz with L 4100.
When switching over to Fe or FeCr, frequency deviation must
not exceed a maximum of 2 kHz.
RF wave traps
Connect a thermionic voltmeter to test point 1 or test point 1'
and align to minimum voltage (105 kHz) with L 4000 or
L 4000'.
Maximum permissible difference of alignment in the other direc-
tion is 1/2 revolution.
Bias switching
The following voltage change must be measured with the aid of a
capacitive voltage divider at the record/playback head, with re-
ference to EHF (105 kHz)
Fe = 0 dB
Fe 1, FeCr
Cr 2, Cr
Met.
= +2
dB±0.5dB
+ 4.5 dB± 0.5 dB
= + 8.5 dB± - 0.5dB
Erase head voltage
Measured at the erase head in position Cr02greaterthan >35
Recording
Connect AF oscillator to INPUT and amplifier, voltmeter and
harmonic distortion meter to OUTPUT. Input switch to LINE.
RF biasing
Insert test cassette Cr02 DIN reference medium section
Cr02, RECORD,
or 4
Record 400 Hz and 10 kHz with —20 dB (LED display).
Compare levels on reproduction.
If there is no uniform level, correct RF biasing.
Decreased RF = treble emphasis
I ncreased RF = treble de-emphasis
Any changes of the RF level can be measured directly at the
head via a capacitive voltage divider (1 pF coupling capacity),
test point 2 or test point 2'.
For alignment of track 1 with R 4084
For alignment of track 2 with R 4084'
For alignment of track 3 with R 4082'
For alignment of track 4 with R 4082
Level
Insert Cr02 DIN tape reference medium section.
RECORD, 1> or
Record 400 Hz at 0 dB (LED display) and then compare with
playback level (LED display). If the levels are unequel, alter the
record current until the playback level = record level.
Correction For track 1 use R 4062
For track 2 use R 4062'
For track 3 use R 4064'
For track 4 use R 4064