QSC Audio manual Q205 Lead Stress, Tools and materials required, Test equipment required

Figure 1. Replacement MJE15032, with leads prepped for strain relief

Service Bulletin

Title:	Q205 Lead Stress
Bulletin #:	RMX0001	Issue Date:	May 15, 2002
Models Affected:	RMX 2450	Bulletin Revision:	B

Production Range: 01/2000–05/2002 (serial # 0100xxxxx–0502xxxxx)

Description

Driver transistor Q205 in the RMX 2450 may have been inserted into the circuit board with the leads too taut, causing one or more of them to break when subjected to vibration and strain caused by handling and other normal usage.

This bulletin describes the procedure for removing the old transistor and replacing it with one whose leads have been prepped to provide a sufficient amount of strain relief. In this new revision of the bulletin, we also recommend removal of the circuit board mounting screws that are closest to transistors Q105 and Q205, even if the amplifier’s transistor leads are not damaged, in order to allow the circuit board to flex more and thus put less stress on the transistor leads.

Symptoms

After the amplifier is turned on, channel 2’s clip LED lights constantly or intermittently, regardless of signal.

Instructions

Replacing transistor Q205 requires removal of the amplifier’s top cover and some minor disassembly. No circuit boards need to be removed.

Tools and materials required:

• Soldering iron with fine tip (recommended range 25 to 60 W)

•Rosin-core solder (60/40 or 63/37 eutectic type)

•Long-nose pliers

•#1 and #2 Philips screwdrivers

• Small diagonal cutters

•Desoldering equipment or solder braid

•One prepped MJE15032 transistor (see Figure 1) per RMX 2450 amplifier

Test equipment required:

• Oscilloscope

• 2-ohm resistive load (rated for at least 1200 watts)

•AC ammeter

•Variable AC transformer—e.g., Variac, Powerstat, etc.—rated for 25A (120V) or 12A (230V). Make sure the amplifier and your AC supply are compatible.

•1 kHz audio sine wave generator

•Digital multimeter

•Trimpot adjustment tool (non-conductive)

Procedure: Removing mounting screws

1. Disconnect the amplifier from AC and wait at least 10 minutes for internal voltages to bleed down. Remove the screws (thirteen #8 screws on the sides and four #4 screws on the top) from the top cover of the chassis. Lift the rear edge of the cover until you can unhook the front edge from the chassis, then remove the cover.

2. Locate transistor Q205. As viewed from the front of the amplifier, Q205 is attached to the left side of the heat sink and is the transistor nearest to the front faceplate.

3. There is a multi-pin connector, J204, joining a ribbon cable to the circuit board next to Q205. Disconnect it from the board to provide better access to the transistor.

4. Remove the mounting screw next to Q205 that fastens the circuit board to the chassis standoff. Also remove the screw next to Q105 on the other channel module. These screws will be left out when you reassemble the amplifier.

RMX0001 Rev. B 1