Tools and materials required | QSC Audio ISA 450, ISA 500T, ISA 800T

Tools and materials required (continued):

•Desoldering equipment or solder braid

•Four 4.7-volt ¼-watt zener diodes (Microsemi DZ840731ET/R; QSC part number QD-0004.7-ZT)

Test equipment required:

•Oscilloscope

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

•Wire or other means of shorting the amplifier output

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

•1 kHz audio sine wave generator

•Digital multimeter

•AC current probe (e.g., BK Precision model CP-1)

•Trimpot adjustment tool (non-conductive)

Note: The circuit boards in the ISA 750 and ISA 800T are double-sided, while those in the ISA 450 and 500T are single-sided. Therefore, to minimize disassembly, this bulletin recommends two different procedures among these models:

D107 & D210: 0.15–0.2"

3.8–5.1 mm

D207 & D110:

0.3"

7.6 mm

0.4"

10.2 mm

Figure 1. Prepare the leads of the new zener diodes.

•In the ISA 750 and ISA 800T, the zener diodes will be unsoldered and soldered from the component side. The instruc- tions for this procedure begin below.

•In the ISA 450 and ISA 500T, the new zener diodes will be soldered “piggyback”-style to the old ones. The instructions for this procedure begin after those for the ISA 750 and ISA 800T.

Procedure: Replacing zener diodes in an ISA 750 or ISA 800T amplifier

1. Disconnect the amplifier from AC and wait at least 10 minutes for internal voltages to bleed down. Remove the top cover.

2. Prepare the new zener diodes as shown in Figure 1.

3. Remove the four screws on the bottom of the amplifier that fasten the heat sink to the chassis.

4. Remove the three screws that attach the channel module assembly to the chassis standoffs.

5. Lift up the front of the channel module assembly. Rotate it so that channel 1’s module (the lower one) is on top; set the assembly down in the chassis with the heat sink resting on the standoffs (Figure 2).

6. Disconnect the ribbon cable from the channel 1 module.

7. Locate zener diode D107. It is near where three wires are soldered to the circuit board and secured with hot glue. If the hot glue covers the diode, use the tip of your hot soldering iron and a small screwdriver to melt and clear the glue away (Figure 3).

8. Notice the orientation of D107. Unsolder and remove it; be careful not to damage the through-plating in the holes. Install and solder a new zener diode oriented in the same direction. Do the same with zener diode D110.

9. Reattach the ribbon cable and turn the channel module assembly back over so that the channel 2 module is on top.

10. Locate zener diode D207 and notice its orientation. Carefully

Figure 2. Prop the channel module assembly up on the chassis standoffs.

Figure 3. You might need to clear hot glue away from diode D107. Use your hot soldering iron tip.

ISA0001

ISA 750, ISA 450, ISA 500T, ISA 800T specifications

QSC Audio, a renowned name in professional audio solutions, offers a range of power amplifiers designed to deliver high performance, reliability, and user-friendly operation. Among their product line, the ISA series stands out, particularly the ISA 800T, ISA 500T, ISA 450, and ISA 750 models. These amplifiers are tailored for various applications, making them ideal for sound reinforcement in live events, small venues, and installations.

The ISA 800T is a powerful amplifier featuring a robust design that can deliver up to 800 watts of power per channel at 4 ohms. This model uses advanced feedback topology and has built-in thermal and short-circuit protection, ensuring reliability and longevity in demanding environments. The ISA 800T also provides features like selectable low-frequency filter, high-pass filter, and variable speed fan control, which enhance its versatility in different applications.

The ISA 500T model, offering 500 watts per channel, is perfect for smaller venues, yet it doesn’t compromise on quality. This amplifier also employs the same advanced feedback topology, providing pristine audio reproduction while maintaining low distortion levels. The ISA 500T offers a variety of input options, including XLR and TRS connections, allowing easy integration into existing audio systems. The compact form factor makes it a favorite for mobile setups and permanent installations alike.

The ISA 450 is another noteworthy addition to the series, designed to cater to smaller systems. It offers 450 watts per channel at 4 ohms and features a similar well-engineered design as its higher-powered counterparts. The ISA 450 is equipped with thermal and overload protections, enabling operation without worry in challenging environments. A unique characteristic of this model is its efficient power consumption, making it an eco-friendly option.

Finally, the ISA 750, with 750 watts per channel, bridges the gap between the ISA 500T and ISA 800T, providing a perfect balance of power and flexibility. It incorporates intuitive controls and connectivity options while maintaining the hallmark features of the ISA series.

All ISA series amplifiers utilize QSC’s rigorous engineering, ensuring they not only meet but exceed the demands of audio professionals. Each model is designed for modularity and durability, ready to endure the rigors of tour life or permanent installation. With their combination of power, reliability, and advanced features, the QSC ISA series amplifiers are an excellent choice for anyone seeking outstanding performance in sound reinforcement applications.

QSC Audio ISA 450, ISA 500T, ISA 800T manual Tools and materials required, Test equipment required

Models: ISA 750 ISA 450 ISA 500T ISA 800T