Technics RS-M250 - Measurement and Adjustment Procedures - Part 2; Playback Gain; Bias Leakage; Erase Current

RS-M250
ITEM MEASUREMENT & ADJUSTMENT
® Playback gain
Condition:
* Tape selector
-++ Normal position
* Playback mode
Equipment:
*VTVM
* Oscilloscope
* Test tape --- QZZCFM
. Test equipment connection is shown in fig. 2.
. Playback standard recording level portion on test tape (QZZCFM 315Hz, 0dB), and using VT VM
measure the output level at LINE OUT jack.
. Make measurement for both channels.
Standard value: 0.7V+1.5dB
Adjustment
L,
2,
If measured value is not within standard, adjust VR3 (L-CH), VR4 (R-CH) (shown in fig. 1).
After adjustment, check “Playback frequency response” again.
@ Bias leakage
Condition:
* Record mode
* Input level controls --- MAX
* Output level control --- MAX
* Tape selector
-+- Metal position
Equipment:
* VTVM * Oscilloscope
1. Test equipment connection is shown in fig. 7.
2.
3. Adjust trap coils L1 (L-CH), L2 (R-CH), so that measured
Record/playback
Place UNIT into record mode.
value becomes minimum.
_
Make
adjustment
for
both
channels.
to
POT
VTVM Oscilloscope
: R149 (L-CH)
Fig. 7 R150(R-CH)
TP3 ee
TPA (R-CH)
@ Erase current
Condition:
* Tape selector
-++ Metal position
* Record mode
Equipment:
* VTVM
* Oscilloscope
@ Bias current
Condition:
* Record mode
* Tape selector
-++ Normal position
+++ Fe-Cr position
+++ CrO2 position
+++ Metal position
Equipment:
* VTVM
* Oscilloscope
@® Overall gain
Condition:
* Record/playback mode
* Normal position
* Input level controls --- MAX
* Output level control --- MAX
* Standard input level;
MIC +--+ e+e —72+3.5dB
LINE IN --- ~24+3.5dB
Equipment:
*VTVM * AF oscillator
* ATT * Oscilloscope
* Resistor (600 2)
* Test tape
(reference blank tape)
-+QZZCRA for Normal
. Test equipment connection is shown in fig. 9.
. Place UNIT into record mode, and tape selector to normal
. Read voltage on VTVM and calculate bias current by following
. Test equipment connection is shown in fig. 8.
. Place UNIT into record mode and measure voltage at test
point 1.
. Determine erase current with the following formula:
Voltage across both ends of R272
1 (Q)
| Standard value: 145+5mA (Tape selector --- Metal)
VTVM Osciloscope
Fig. 8
Erase current (A)
. If measured value is not within standard, adjust VR9.
€109 (L-CH)
C110 (R-CH):
position.
Record mode
TP7{R17)
formula:
TP8
(R18)
Value read on VTVM (V) VIVM Oscilloscope
102
Standard value: around 330A (Normal position)
Bias current (A)
. Adjust C109 (L-CH) and C110 (R-CH) (shown in fig. 1).
. Set the tape selector to each position.
. Make sure that the measured value is within standard.
Standard value: around 370A (Fe-Cr position)
around 415A (CrOz position)
around 700A (Metal position)
. Test equipment connection is shown in fig. 10.
. Place UNIT into record mode, and normal tape mode.
. Supply 1kHz signal (—24 dB) from AF oscillator,
. Adjust ATT until monitor level at LINE OUT becomes
. Using test tape, make recording.
. Playback recorded tape, and make sure the value at
. lf measured value is not 0.7 V, adjust VR5 (L-CH),
through ATT to LINE IN.
Record mode
LINE IN
AF oscillator 1
tt
0.7V. ies
R/P head
Pa
k =
Playback mode “VTVM
Fig. 10
LINE
OUT
on
VTVM
becomes
0.7
V.
vad
tie
Oscitloscope
VR6 (R-CH).
. Repeat from step 2.