Test Mode - Roland CPM-300 Service Notes

CPM-300

TEST MODE

CPM-300 Adjustment
• • • •
Checking operation of high-efficiency power amplifiers
The CPM-300 has high-efficiency power amplifiers fabricated
through the ECOS technology.
This section explains how to check and adjust these high-effi-
ciency amplifiers.
Carry out the checking/adjusting procedure described below
whenever the power amp board has been repaired or
replaced.
♦
Adjusting ±Va
1. Setup
INPUTS - - - - - - - - - - - - - No signal
SPEAKERS - - - - - - - - - - Open
MASTER FADERs - - - - - MIN.
The Effect board can be left removed for the purpose of
adjustment because it is not involved in the adjustment.
2. Adjustment
Connect the probes of a dual channel oscilloscope across the
following points:
• • • •
Power amp board
+Va: EMI bead L12 and GND
-Va : EMI bead L14 and GND
Adjust VR5 for +Va and VR6 for -Va so that +7 V and -7 V are
obtained, respectively, between the trough of the waveforms
and ground reference (DC components).
(See Figure 1.)
Make the exact adjustment. If a voltage is out of spec, it
causes undesirable amp operation:
• • • •
A higher Va causes the power transistor to generate more
heat, decreasing the efficiency.
• • • •
A lower Va causes the power transistor to distort the signal.
♦
±Va waveform specifications
1. Setup
INPUTs - - - - - - - - - - - - - Connect CH 1 (INPUT 1) to an
audio generator
HIGHs, LOWs - - - - - - - - Flat
SENDs - - - - - - - - - - - - - MIN
PANs - - - - - - - - - - - - - - - Center
SPEAKERS - - - - - - - - - - - Into 8-ohm loads, LEFT and RIGHT
SENS's, FADERs, MASTER FADERs
- - - - - - - - - - - - - - - - - - - Adjust as described in the step 2
below.
The Effect board can be left removed for the purpose of
adjustment because it is not involved in the adjustment.
6
Figure 1
2. Monitoring waveforms
Connect the probes from the oscilloscope across the points.
Adjust the frequency and output level (sine wave) of the audio
generator and the panel controls SENS's, FADERs and MAS-
TER FADERs so that the output shown in Figs. 2-5 are
obtained.
Check the +Va and -Va displayed on the scope against the
figures shown in Figs. 2-5.
• • • •
Power amp board
+Va: EMI bead L12 and GND
-Va : EMI bead L14 and GND
Fig. 2 SP OUTPUT: 28.3 Vrms, 1 kHz`
Fig. 3 SP OUTPUT: 28.3 Vrms, 4 kHz
Fig. 4 SP OUTPUT: 28.3 Vrms, 6 kHz
Apr,1999