QSC Audio DSP-4 RS-232 manual Description, Symptoms, Instructions, Tools and materials required

	Service Bulletin
Title:	DSP-4 RS-232 Communication/Turn-Off Thump
Bulletin #:	DSP0009
Issue Date:	July 27, 2006
Models Affected:	DSP-4
Bulletin Revision:	Rev. A
Production Range:	05/2001 through 05/2006 (serial numbers 0501xxxxx–0506xxxxx)

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

Tools and materials required:

•#2 Philips screwdriver

•Small boxes or compartments (to hold assorted screws during disassembly)

•Small diagonal cutters

Figure 1. The problems may occur when these two screws are tightened.

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.

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DSP0009 rev. A. 1