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(4) High Frequency Response Check and Adjustment
Cautions:
e@ Be sure to check the frequency response after the head assembly is replaced.
@ If the frequency response does not fall within the limits, perform the following adjustment.
Frequency Response Check
1. Play back 250Hz, -20dB and 12.5kHz, -20dB of the ACC Test Tape (SBC420) forward, and verify that
the level difference between the two bands is within 0 + 1dB.
2. Reverse the direction of tape transport and perform the same check.
Test tape and tool required
Measuring instruments required
1. ACC test tape (SBC420)
1. Frequency counter
2. Ceramic screwdriver
2. Electronic voltmeter (EVM)
(HOZAN D-281,@No. 1.7)
(AC range)
EVM
Lch: OUT (LINE OUT)
(AC range)
Reh: OUT (LINE QUT)
0CC170
Frequency
counter
@ Adjustment Procedure
1. While playing back 250Hz, —20dB of ACC Test Tape (SBC420) forward, measure the LINE OUT levels
on both channels. Use these levels as standards.
Play back 12.5kHz, -20dB of the same test tape forward, and adjust R151 (L ch) and R152 (R ch) until
the LINE OUT levels are identical to the standard levels obtained above.
Adjustment Target: 0 +0.5dB
. Reverse the direction of tape transport and perform the same check.
Check Target: 0 +1.5dB
(5) Recording Current Adjustment
@ Always perform the adjustment when the head block is replaced.
Test tape and tool required
Measuring instruments required
. DCC test tape
1. Digital voltmeter (Dig.-vol.)
(9.6kHz level tape)
2. Oscilloscope
- DCC blank tape
. Ceramic screwdriver
(HOZAN D-281,@No. 1.7)
2.
TP: J202
* Recording
(C SET)
Dig-Vol. (DC range)
pcc170
pee
TP: J112
(RDSYNC)
0CC170
« Play back
. Press the STOP button twice to turn the unit OFF.
. Short lands of TPO1. (Refer to Fig. 1 MECHANISM
PCB.)
. Play back the DCC test tape (9.6kHz, O0dB).
. Measure that the TP: J110 (peak to peak level),
J110:RDMUxX level by Oscilloscope. Use this level
Memorized
as standard.
a
y level
. Next, change the DCC test tape to a DCC blank
tape and set the unit to the recording status.
(Record music signals.)
. Adjust R211 until voltage value at TP: J202 shows
130mV~ 140mVDC. (Temporary adjustment)
—CH2
CH1: 2V:DIV. 0.5ysec DIV
CH2: 0.5V/DIV. 0.5,sec DIV
* Triggerd by CH1.
TP: 3110
(RDMUX)
8. If the value is out of the limit, repeat steps 5 ~ 7.
«If the level is higher than the reference level,
rotate R211 counterclockwise to decrease the
voltage (C SET) at J202.
+ If the level is lower than the reference level,
rotate R211 clockwise to increase the voltage
(C SET) at J202.
9. Open the short-circuit at lands of TP01.
Caution:
For each head, a recommended recording current exists
aa
mos:
. Play back the music signals recorded in the step 6,
and measure the voltage at TP:J110 again (peak to
peak level). Check this level and the standard level
in 4, to see their level difference is within 0£100mV.
Adjustment Target: 0 +100mV
PCS 79 280
individually. If this value is not adjusted correctly, the
RDMUX value does not match between a self recorded
tape and prerecorded tape. Moreover, if a recording is
made at a deep layer with a high value, the previous
records can not be erased when an overwrite recording is
made at that area later. As a consequence the error rate will
be increased at that area.
=o
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