Teac A-400 - Specified Output Level Setting; Level Meter Indication Checks; Playback Frequency Response Checks

4-2-2. Specified Output Level Setting
1. Connect a VTVM between the Dolby T.P. (test points) an
Ground on the REC/PB amplifier PC Board. :
Load a TEAC MTT-150 test tape on the deck.
Play Dolby tone in the tape.
Adjust VR101/VR201 for 580 mV (-2.5 dB) on the VTVM.
Connect the VTVM to the OUTPUT jacks. ~
Turn the OUTPUT controls fully clockwise.
Confirm that the output level is +9 dB + 2 dB (1.73 V ~ 2.74
V).
8. Set the OUTPUT controls for a reading of +3 dB (1.09 V) on
NOP wen
-2.5dB(580mv)
VRioI/VR201
DECK under TEST (PLAY mode)
v
the VTVM. This is the specitied output level.
IMPORTANT
After setting the specified output level, do not disturb the
OUTPUT controls until the remaining adjustments and checks
have been completed.
4-2-3. Level Meter indication Checks
9. After setting the specified output level, make certain that the
indications on the level meters of the deck are +3 VU + 1.5
VU.
4-2-4. Playback Frequency Response Checks
10. Load a TEAC MTT-116L test tape.
11. Play the test tones from 40 Hz up to 10 kHz.
12. Check that the reading obtained on the VTVM is within the
response limits in reference to the 333 Hz/—10 dB signal
section of the tape.
NOTE
If the response does not meet specified response limits, the head
should be checked for accumulated oxide or dirt. Then, if no
dirt is found, the head azimuth should be readjusted.
4-2-5. Signal-to-Noise Ratio Checks
The S/N ratio should be: 47 dB (minimum)
IMPORTANT
Prior to these checks, confirm that the OUTPUT controls are at
specified output level position.
1. Connect a VTVM to the OUTPUT jacks.
2. Place the deck in the PLAY mode with no tape loaded.
3. Read the indication on the VTVM connected to the
OUTPUT jacks. ;
NOTE
Since the polarity of the AC plug has some effect on the S/N
ratio, the plug can be reversed in the wall socket when checking
the S/N ratio. The worse case value should be within the
indicated value above.
Next
set
for
+3dB.
(Specified
OUTPUT
Control
Setting)
OSCILLOSCOPE
DOLBY NR’
VRioi/VR201
DECK
under
TEST
(PLAY
mode
)
aoe
Fig.
34
Test
Condition
for
Specified
Qutput
Level
Setting
OSCILLOSCOPE
T>
389
DECK
under TEST
RESPONSE IN dB
“4 1 i HN al
i
|
250 333 500 1K 2K
FREQUENCY IN Hz
40
50
100°
ak
5K
63K
10K
Fig. 36 Playback Frequency Response Limits
4.
The
VTVM
should
indicate
-44
dB
min.
(4.88
mV
maximum).
5.
This
corresponds
to
a
signal-to-noise
ratio
of
47
dB
(mini-
mum):
difference
between
residual
noise
44
dB
(4.88
mV)
and
the
specified
output
level
+3
dB
(1.09
V).
16 ? NOTE: For actual adjustment/test point locations, see page 21.