Bias Trap Adjustment - Tascam 133-B Service Manual

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1) Connect a level meter to terminals OUTPUT
(except for the CUE track).
2) Playback Test Tape MTT-356 and check that
the output level stays within the specified
boundaries {see Fig. 6-3) over the entire fre-
quency range.
- azimuth again.
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PT
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FREQUENCY IN He
RESPONSE 0A 48
Fig. 6-3. Playback frequency response
6-4. BIAS DUMMY COIL ADJUSTMENT
1) Connect.a.frequency counter to test point -TP2 .
at bias oscillator U401,
2) Load the deck with a blank test tape. Set all
FUNCTION REC/MORMAL switches at REC
and select REC/PAUSE mode with operating
buttons. ;
3) Check bias frequency (fo).
NOTE: The fo.is.a.bias frequency value deter-
mined when all the FUNCTION switches
of every channels (L, R, and CUE) are set
at REC, with the dummy coil in a non-
operating state.
4) Resetting:-4:-channel (S103) alone to NOR-
MAL, adjust L401 until the bias frequency
becomes fo.
5) Resetting R-channel (S203) alone to NOR-
MAL, adjust L402 until the bias frequency
becomes fo.
6) Resetting CUE channel (S303) alone to NOR-
MAL, adjust L403 until the bias frequency
becomes fa.
7) Check that the bias frequency stays within
+506 Hz of fo at any combination of settings
of the REC/NORMAL switches ($103, S203,
and $303).
6-5. BIAS FILTER ADJUSTMENT
1) Connect a level meter to terminals OUTPUT
(L/R/CUE).
_ is —10.dBV +1 dB and the +4 dBm BAL
- OUTPUT. terminal level is +4-dBm +1-dB.
R249 so that the meter of the L/R-channel
read +3 VU, and semi-fixed variable resistor
R349 so that the CUE meter reads O dB.
6-7. BIAS TRAP ADJUSTMENT
6-B. BIAS ADJUSTMENT
Make the following preparation for adjusting
bias.
a. Connect measuring instruments as shown in
Figure 6-1.
b. Load the deck with Test Tape MTT5061 and
put it in REC/PAUSE mode.
c. Set the REC/NORMAL switch of every chan-
nel at REC,
d. Apply 400 Hz, —11 dB (282 mV) to input
terminals L, R, and CUE.
e. Set the OUTPUT control of every channel at
its maximum position.