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Make sure your AC supply is appropriate for the amplifier. • 1 kHz audio sine wave generator D107 & D210: • Digital multimeter • AC current probe (e.g., BK Precision model CP-1) D207 & D110: • 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 Figure 1. Prepare the leads of the recommends two different procedures among these models: new zener diodes. • In the ISA 750 and ISA 800T, the zener diodes will be unsoldered and soldered from the component side. The instructions 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 0.3" 7.6 mm 0.4" 10.2 mm 0.15–0.2" 3.8–5.1 mm 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 unsolder and remove it. Install and solder a new zener diode oriented in the same direction. Do the same with diode D210. 11. Check your work. Don’t reattach the channel module assembly and heat sink to the chassis yet. Instead, continue with the bias and current-limit calibration. New 4.7-volt zener Old 5.6-volt zener Figure 4. Solder a new zener diode “piggyback”-style onto each old one. Procedure: Installing new zener diodes in an ISA 450 or ISA 500T amplifier 1. Disconnect the amplifier from AC and wait at least 10 minutes for internal voltages to bleed down. Remove the top cover. 2. Remove the four screws on the bottom of the amplifier that fa...

Other models in this manual:
Car Amplifiers - ISA ISA 450 (595.46 kb)
Car Amplifiers - ISA ISA 750 (595.46 kb)
Car Amplifiers - ISA ISA 800T (595.46 kb)

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