Record Bias Setting Adjustment; Record Level Setting; Distortion Checks - Teac C-1 Service Manual

6-6-2. RECORD BIAS SETTING ADJUSTMENT
CrO, tape
1.
wo
nA
Connect the deck and the test equipments as shown in
Fig. 6-9 on page 21.
. Load a TEAC MTT-506 test tape.
. Set the attenuator so that the input to the deck is —42
dB (6.15 mV).
. Initially set the R865/R866 fully counter clockwise.
. Record a 6.3 kHz test tone.
. Turn R865/R866 slowly clockwise so that the output
reading on the AC voltmeter rises slowly, reaches a peak,
and then begin to decrease again. Set both trim pots for
1 dB beyond and below the peak level.
. Then apply and record two tone signals in turn, a 400 Hz
signal and a 15 kHz signal.
. During simultaneous tape monitoring (playing), compare
the output level of the 15 kHz signal with the level of
the 400 Hz signal. Both signals should indicate almost
the same level.
. Adjust R865/R866 until this (#8) requirement is satisfied.
10.
11.
Then record an 18 kHz signal on the tape.
While watching the AC voltmeter, make fine adjusting
by turning L307, of both L- and R-channels, so that the
18 kHz signal level satisfies the frequency response limits
in Fig. 6-14.
FeCr and NORMAL tapes
12. Repeat the preceding procedure, with the following dif-
ferences:
FeCr tape NORMAL tape
BIAS/EQ switches: FeCr NORMAL
Test tape: MTT-504 MTT-501
Adjustment for BIAS: R863/R864 R861/R862
Adjustment for freq.
spec.: L306 L305
Different freq.
in step 10, 11: 18 kHz 16 kHz
Peak
| 6.3kH; 1dB
2 |
5 \
&
i
Fs '
&
3
22
a? 1 dB over -bias position.
BIAS CURRENT ———>
Coarse adjustment
Fig. 6-11 Bias adjustment (coarse)
i Obtain this position to get
OPTIMUM VALUE no difference in output level
between two signals.
OUTPUT RESPONSE ——-»
BIAS CURRENT ———
Fine adjustment
T-1488
Fig. 6-12 Bias adjustment (fine)
6-6-3 RECORD LEVEL SETTING
CrO, tape =
13. Set the BIAS/EQ switches to the CrO, position and load :
a TEAC MTT-150 test tape.
14. Play the tape and make sure that levels from OUTPUT
jacks are —5 dB (436 mV).
15, Change tape MTT-506.
16. Apply and record a 400 Hz test signal at —12 dB (195
mV).
17. Then conduct simultaneous record/playback monitoring.
18. Adjust R364, of both L- and R-channels until the deck's
output indicates —8 dB (308 mV).
FeCr and NORMAL tapes
19. Repeat the above procedures using the following substitu-
tions.
FeCr tape NORMAL tape
BIAS/EQ switches: FeCr NORMAL
Test tapes: MTT-504 MTT-S501
Adjustments: R366 R367
6-6-4 DISTORTION CHECKS
Specifications:
2.0% or less (with all kinds of tape)
OSCILLOSCOPE
AC Voitmeter
Te5Res
Fig. 6-13 Connection