Dual C 822 Serviceanleitung Seite 5

DUAL C 822-electrical alignemnt
Necessary instruments and test cassettes
2 millivoltmeters
1 AF oscillator
1 oscilloscope
1 frequency counter
1 test cassette 400 Hz - 20 dB, 10 kHz — 20 dB
1 test cassette 400 Hz Dolby level 200 mWb/m
1 test cassette Cr reference medium section (e.g. BASF
chrome dioxide, C 60)
1 test cassette Fe reference medium section (e.g. BASF
super LH, C 60)
1 test cassette Fe-Cr reference medium section (e.g. Sony
Fe Cr Duad, C 60)
1 test cassette metal reference medium section (e.g.
Scotch Metafine C 46)
General notes
The magnetic head and all ferrous components which come into contact
with the tape must be magnetized.
Readjustment must be carried out in the sequence stated.
The L 101 and L 101' multiplex filters are set precisely at the factory
and must not be readjusted.
Playback
Magnetic head adjustment
Remove the screws 11 on the front trimplate. Remove the cassette com-
partment frame by pressing it in at the side, insert the test cassette (sec-
tion determined for gap adjustment) 10 kHz —20 cB.
Connect the millivoltmeters to outputs L and R (cinch connectors ). If
only one millivoltmeter is available, switch the outputs in parallel.
Fe, >
Using the adjustment screw to the left of the magnetic head, adjust for
maximum voltage.
After alignment, jock the adjusting screw in position using locking com-
pound. .
Note:
tf the outputs are arranged in parallel, secondary peaks will occur. In this
case, adjust for the main peak.
The difference between channel L and channel R at 10 kHz <3dB.
Playback level
insert test cassette, 400 Hz Dolby level
Fe, Dolby: On, MPX: Off,
{In each case, set 580 mV £0.25 dB
for track 7 using VR 103 at cinch output L
for track 2 using VR 103' at cinch output R
Playback frequency
Insert test cassette, 400 Hz — 20 dB, 10 kHz — 20 dB
Fe, (Dolby: Off, MPX: Off) >
Both level components of the test cassette should have the same output
voltage at outputs L and R. If a voltage rise is determined in the case of
the 10 kHz — 20 GB level in relation to the 400 Hz — 20 cB level, connec-
tions J 1 and J2 or J 1' and J 2' must be disconnected.
lf the 10 kHz — 20 dB level is lower than the 400 Hz — 20 GB level,
connections J 1 and J 2 or J 1' and J 2' must be connected.
The output voltage at outputs L and R must be between +4 and —3dB
at 10 kHz, referred to the 400 Hz — 20 dB level (corresponds to reference
point O dB).
VU meter
Fe, record, Dolby: On >»
Connect the AF oscillator to the input and the millivoltmeter (AC)
to the output. Set modulation controis VR 101 and VR 101° to fully
clockwise position.
Set the AF oscillator to 400 Hz and adjust the input signa! at the cas-
sette deck in order to obtain a reading of 580 mV at outputs L and R.
Using VR 104 and VR 104' respectively, set the VU meter left channel
and the VU meter right channel to +3 dB modulation.
Background noise
Screen the amplifier and ensure that the magnetic head is free of hum.
Fe, pause, >
Background noise at outputs L and R 3 mV maximum measured with a
20 Hz filter (e. g. Sennheiser FO 55, curve 220 Hz — 3 dB) with rms
rectification of meter.
HF generator
Met, record, >
Connect the frequency counter between test point D and ground and then
adjust the core of the oscillator coil {L 301) to obtain a reading of 105 kHz.
Connect the millivoltmeter (AC) to test point D and ground. The vol-
tage drop at R 301 should be greater than 150 mV.
HF wave traps
Connect the millivoltmeter (AC) or oscilloscope to R 143 (left channel)
or R 143' (right channel} and, using coil L 103 or L 103', set to minimum
HF voltage.
HF magnetic bias
Insert test cassette, Cr reference medium section,
Cr, record,
A millivoltmeter (AC) may be connected between test point E (left chan-
nei) or E* (right channel) and ground for basic adjustment. Using VR 105
or VR 105', set a voltage of 7O mV.
Depending upon the setting of the tape selector switch, the following
voltages will result:
Fe Approx. 4A2mV=~—45dB
Cr 70 mV = 5 dB
FeCr Approx. 53 mV =—2.5dB
Met 1117 mV=+ 4dB
Tolerance +0.5 dB
Precise alignment must be performed as follows:
Record 400 Hz and 10 kHz with 25 dB (VU meter) {with Cr reference
medium section). Compare the levels during playback.|f the jevel of both
frequencies is not uniform, correct HF bias.
Track 1 (left channel) is adjusted using VR 105 and
Track 2 (right channel) using VR 105'.
Decreased HF = treble emphasis.
Increased HF = treble de-emphasis.
Insert test cassette, Fe reference medium section (BASF super LH, C 60)
Fe, record, >
Record 400 Hz and 10 kHz with — 20 dB (VU mete) . if a voltage rise
of the 10 kHz level in relation to the 400 Hz level is determined during
playback, connect J 7, Otherwise, i. e. in the case of avoltage drop, dis-
connect resistor R 308.
insert test cassette, metal reference medium section (Scotch Metafine
C 46)
MET, record, »
Record 400 Hz and 10 kHz with -- 25 dB (VU meter!. Compare the le-
vels during playback. If a voltage rise of the 10 kHz evel in relation to
the 400 Hz level is determined, connect J 8. Otherwese, disconnect R
314.
Record level
Insert test cassette, Cr reference medium section
Cr, record, Dolby: On, »
Record 400 Hz with O dB (VU meter) and then check ine playback fevel
at the VU meters.
Using VR 102 (VU meter left) and VR 102' (VU mete right), adjust the
recording current so that the playback level = record bvel. (Approxima-
tely 410 mV should be measured at cinch outputs L aicf R).
Insert test cassette, Fe reference medium section
Fe, record, Doiby: On, >»
Record 400 Hz with 0 dB (VU meter) and then cteck the playback
level at the VU meters. if the playback level is hiqver, connect J 3
(R 132) and J 3' (132'). If the output level is lower, csconnect resistor
R 134 or R 134'.
FeCr,
Insert cassette (e.g. Sony, ferrichrome)
FeCr, record, Dolby: On, >»
Record 400 Hz with O dB (VU meter) and then cleck the playback
level at the VU meters. If the payback level is higher, aranect J 4 or J 4'.
lf the output jevel is lower, disconnect R 131 or R 13)'.
Insert MET cassette { e.g. Scotch Metafine)
MET, record, Dolby: On, »
Record 400 Hz with 0 dB (VU meter) and then cleek the playback
level at the VU meters. If the Playback level is highe , connect J 5 or
J 5'. If the output level is jower, disconnect R127 ork 127'.
Overall frequency response
The overall frequency response for all types of tape nuust lie within the
specified tolerances in accordance with DIN 45 500, Seet 4. Recording
is carried out at a _ level of approximately —26 dB ag ndicated on the
VU meters.