Roland JC-40 Service Notes page 17

Nov. 2015
Input/Output Check
1.
Disconnect the speaker wiring from the L and R speaker terminals.
* If the speakers are connected, when the VIB/CHORUS knob is set to VIB on the next step, sound is produced at high volume.
* Be very careful so that the speaker terminals never touch to the other metal portion.
2.
Set the VIB/CHORUS knob as shown in the table below, and verify that the output corresponding to the appropriate input can be achieved.
VIB/CHORUS Input jack
knob
VIB INPUT L/MONO
VIB INPUT R
VIB INPUT L/MONO
VIB INPUT R
OFF INPUT L/MONO
OFF INPUT R
MANUAL EFFECT LOOP RETURN L/MONO
MANUAL EFFECT LOOP RETURN R
MANUAL EFFECT LOOP RETURN L/MONO
MANUAL EFFECT LOOP RETURN L/MONO
MANUAL EFFECT LOOP RETURN R
MANUAL EFFECT LOOP RETURN R
MANUAL EFFECT LOOP RETURN L/MONO
MANUAL EFFECT LOOP RETURN R
* When the sound is input to the INPUT L/MONO jack, connect the dummy plug to the INPUT R jack, and when the sound is input to the INPUT R jack,
connect the dummy plug to the INPUT L/MONO jack. And also, when the output signal from the LINE OUT L/MONO jack is checked, connect the dummy plug
to the LINE OUT R jack, and when the output signal from the LINE OUT R jack is checked, connect the dummy plug to the LINE OUT L/MONO jack.
* When the output from the PHONES jack is checked, connect 33Ω load resistors between L and GND, and between R and GND.
Speaker Output Check (Reference)
1.
Adjust the VIB/CHORUS knob to MANUAL.
2.
Connect a 4Ω load resistor to the L-channel speaker wirings (red and
black).
* If the resistor can not be prepared, connect the speaker instead.
3.
Connect the noise meter to the L-channel speaker wirings.
4.
Connect the oscillator to the EFFECT LOOP RETURN L/MONO jack and
connect the dummy plug to the R jack.
5.
Input the following signal to the EFFECT LOOP RETURN L/MONO jack.
RETURN L/MONO:1-kHz sine wave at -40 dBm
6.
Verify that the output value of the speaker wirings is +7.5 dBm or higher.
* When the value above can not be achieved, change the dummy plug connected to
the RETURN R jack to the short plug.
7.
Detach the noise meter and connect the oscilloscope.
8.
Input the following signal to the EFFECT LOOP RETURN L/MONO jack.
RETURN L/MONO:1-kHz sine wave at -20 dBm
9.
Verify that the output waveform from the speaker terminal is distorted as
shown in the figure below.
fig.test.eps
10. For the R-channel speaker wirings, verify in the same way as steps 2
through 9.
* Color of the R-channel speaker wirings are brown and orange.
* Connect the dummy plug to the EFFECT LOOP RETURN L/MONO jack and
input the signal to the R jack.
11. Detach the oscillator and the oscilloscope.
12. Connect the speakers as they were.
Input signal Output jack
(1 kHz, sine wave)
-40 dBm LINE OUT L/MONO
-40 dBm LINE OUT R
-40 dBm EFFECT LOOP SEND
-40 dBm EFFECT LOOP SEND
-40 dBm EFFECT LOOP SEND
-40 dBm EFFECT LOOP SEND
-40 dBm LINE OUT L/MONO
-40 dBm LINE OUT R
-40 dBm PHONES L
-40 dBm PHONES R
-40 dBm PHONES L
-40 dBm PHONES R
-10 dBm PHONES L
-10 dBm PHONES R
Residual Noise Check (Reference)
1.
Adjust the VIB/CHORUS knob to OFF.
2.
Verify that the residual noise at the EFFECT LOOP SEND jack is as
follows.
-65 dBm or lower (DIN-audio)
3.
Verify that the residual noises at the PHONES jack (L and R) are as
follows.
L: -65 dBm or less (DIN audio)
R: -65 dBm or less (DIN audio)
4.
Verify that the residual noise at the L channel of the speaker is as follows.
-35 dBm or lower (DIN-audio)
5.
Verify that the residual noise at the R channel of the speaker is as follows.
-35 dBm or lower (DIN-audio)
JC-40
Output value
+7.5±2 dBm
+7.5±2 dBm
-1.5±2 dBm
-1.5±2 dBm
-31.5±2 dBm
-31.5±2 dBm
-16±2 dBm
-16±2 dBm
-18±2 dBm
-22±2 dBm
-22±2 dBm
-18±2 dBm
(verify that the sound clips)
(verify that the sound clips)
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