QSC Audio Stereo System DSP 4 RS 232 User Guide

Service Bulletin  
Title:  
Bulletin #:  
DSP-4 RS-232 Communication/Turn-Off Thump  
DSP0009  
Issue Date:  
July 27, 2006  
Models Affected:  
Bulletin Revision:  
Production Range:  
DSP-4  
Rev. A  
05/2001 through 05/2006 (serial numbers 0501xxxxx0506xxxxx)  
Description  
When a DSP-4 unit is mounted directly to a QSC single DataPort equipped amplifier and the two long screws shown in Figure 1 are  
tightened, the torque bends the two internal PCB boards slightly. This causes the leads from U7 (a 20-pin DIP microcontroller) to  
touch the top of capacitors C42 and C45, causing communication and audio problems. To correct this inadvertent connection, trim all  
20 of U7’s lead pins.  
Symptoms  
When mounted directly to a QSC single DataPort-equipped  
amplifier and the two #4-40 screws shown in Figure 1 are tight-  
ened, the DSP-4 may exhibit any of these problems:  
• Loss of RS-232 communication with the computer and the  
Signal Manger software  
• A thump on the output signals during turn off.  
• A buzz in the output signals.  
Instructions  
Figure 1. The problems may occur when these two screws  
are tightened.  
Tools and materials required:  
• #2 Philips screwdriver  
• Small boxes or compartments (to hold assorted screws during  
disassembly)  
• Small diagonal cutters  
Caution: Take appropriate anti-static measures to guard against damage from electrostatic discharge (ESD).  
Procedure: Trimming the leads on the microcontroller U7  
Gaining access to the IC  
1. Disconnect the DSP-4 from the amplifier.  
2. Remove all 14 screws on the front panel of the DSP-4. Turn the DSP-4 on its  
side and remove the other two screws, then flip the DSP-4 over (Data Port  
receptacle side) and remove the remaining ones. Note that there are four  
different screw sizes.  
3. Gently and carefully pull the chassis apart and remove the printed circuit  
board (PCB) assembly.  
4. Separate the two PC boards and locate the one with the QSC part number  
that begins with WP-000411-.  
5. Locate the microcontroller U7. See Figure 2.  
6. Use small diagonal cutters to trim all 20 leads of U7.  
Figure 2. Locate the microcontroller U7.  
Continued on next page  
DSP0009 rev. A.  
1
 

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