Panasonic RS-B25 - Erase Current Adjustment

@ Erase current Condition:
¢ Record mode
¢ Metal tape mode
RS-B25
Equipment:
¢ EVM (Electronic Voltmeter)
¢ Oscilloscope
. Test equipment connection is shown in fig. 9.
. Place UNIT into metal tape mode.
. Press the record and pause buttons.
. Read voltage on EVM and calculate erase current by
formula:
Voltage across resistor R301
1 (2)
Standard value: 155+15mA (Metal) (155+ 15mV)
Erase current (A)=
following
5. If the measured value is not within the standard value adjust it by
following the adjustment instructions.
Adjustment
* If the erase current is more than 170mA, cut the jumper wire
(See fig. 1).
@ Overall frequency Condition: Equi
response ¢ Record/playback mode e EV
pment: e Resistor (6002)
M ° Test tape
¢ Normal tape mode (Electronic Voltmeter) (reference blank tape)
¢ CrO, tape mode © ATT ...QZZCRA for Normal
° Metal tape mode ¢ AF oscillator ...QZZCRX for CrO,
¢ Input level controls...MAX © Oscilloscope ...QZZCRZ for Metal
Note:
Before measuring and adjusting, the overall frequency
response make sure of the playback frequency response (For
the method of measurement, please refer to the playback fre-
quency response).
(Recording equalizer is fixed)
1. Make connections as shown in fig. 11.
. Place UNIT into normal tape mode and insert the normal
reference blank test tape (QZZCRA).
. Supply a 1kHz signal from the AF oscillator through ATT to
LINE IN.
. Adjust ATT so that input level is —20dB below standard
recording level (standard recording level = 0 VU).
. Adjust the AF oscillator frequency to 1kHz, 50Hz, 100Hz,
200Hz, 500Hz, 4kHz, 8kHz, 10kKHz and 12.5kHz signals,
and record these signals on the test tape.
. Playback the signals recorded in step 6, and check if the
frequency response curve is within the limits shown in the
overall frequency response chart for normal tapes (fig. 10).
(If the curve is within the charted specifications, proceed
to steps 7, 8 and 9.)
If the curve is not within the charted specifications, adjust
as follows;
shown in fig. 12. B mens oe 10)
1) Increase bias current by (“T= 1)
turning VR301 (L-CH) and [ft turning VR301 (L-CH) and
VR302 (R-CH). 42. 5kHz
(See fig. 1.) mae] | Nite” ||
Repeat steps 5 and 6 for 8kHz 7kHz 8kHz
confirmation (Proceed to :
steps 7, 8 and 9 if the Fig. 12
curve is now within the
charted specifications as shown fig. 10.)
If the curve still exceeds the specifications (fig.
10), increase bias current further and repeat
steps 5 and 6.
Overall frequency response chart (Normal)
TT maaan eels 40B
Tt : ime= sant :
Hop es > HT
5OHz 100Hz 200Hz SOOHz 1tkHz 2kHz 4kHz 10kHz
Fig. 10
EVM Oscilloscope
Pruniniaee tense Notes
(RS-B25) i Nenilineca For overall frequency
EVM Oscilloscope response measurement
For bias voltage .
Adjustment
(A):
Adjustment
(B):
measurement
Fig.
11
When the curve exceeds the Tit 71 When the curve falls below
overall specified frequency 4+—-+—] 5 —| the overall specified fre-
response chart (fig. 10) as H} —>-3 — quency response chart (fig.
as shown in fig. 13.
Reduce bias current by
VR302 (R-CH).
Repeat steps 5 and 6 for
confirmation (Proceed to An TkHZ BH
steps 7, 8 and 9 if the :
curve is now within the Fig. 13
charted specifications as
shown fig. 10.)
If the curve still falls below the charted specifica-
tions (fig. 10), reduce bias current further and
repeat steps 5 and 6.