This problem is most pronounced in the ISA 750 and ISA 800T models, but may also occur in some ISA 450 and ISA 500T amplifiers. Symptoms When the amplifier is turned on, one or both channels remain inoperative, with their respective clip LEDs lit. In some cases, the problem will clear by itself after several seconds. This problem is merely a nuisance and presents no danger to the amplifier, the speakers, or the rest of the sound system. Any one or more of these situations will tend to aggravate

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:

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 fasten the heat sink to the chassis. 3. Remove the three screws that attach the channel module assembly to the chassis standoffs. 4. Locate zener diodes D107 and D110 on the cha

6. Measure the DC voltage across R147. Adjust bias trimpot R131 to reach the correct voltage shown in Table 1. 7. Next, measure the DC voltage across R247. Adjust bias trimpot R231 to reach the correct voltage shown in Table 1. 8. Turn off the amplifier and reattach the channel module assembly and heat sink to the chassis. Current limit adjustment Note: Read through these instructions before proceeding. To avoid tripping the amp’s circuit breaker, work carefully but quickly, and don’t run the am

NOTE: it is normal for the Br Mono indicator LED to transition slowly. •STEREO MODE (Green LED). Each channel operates independently, as usual. •PARALLEL INPUT MODE (Orange LED). The inputs of both channels are hard-switched together, but all controls and speaker connections work as usual. Do not attempt to parallel the output channels to the same load. INPUT SENSITIVITY SWITCH, 3-POSITION: 26dB, 32dB, 1.2V •The 26dB (Orange) and 32dB (Green) settings provide the same voltage gain for all models

GAIN CONTROLS 21 Steps, 1dB Each. 6 QSC DATAPORT Supports QSC DataPort Products. HIGH PASS FILTER SWITCH (Ch1, Ch2) Off (No LED), 30Hz (Yellow), 50Hz (Orange) CLIP LIMIT SWITCH (Ch1, Ch2) Off (No LED), On (Yellow) XLR INPUT CONNECTORS Female and Male, Wired in Parallel for Daisychaining to Additional Equipment. Balanced Inputs, Impedance >10K Balanced: Unbalanced: PLUGGABLE TERMINAL BLOCKS 5.0mm, 3-pin. Paralleled with XLRs Balanced Pinout: Unbalanced Pinout: INPUT MODE SWITCH Bridge (Yellow) Se

3- Heed all warnings. 4- Follow all instructions. 5- WARNING: To prevent fire or electric shock, do not expose this equipment to rain or moisture. Do not use this apparatus near water. 6- Clean only with a dry cloth. 7- Do not block any ventilation openings. 8- Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifiers) that produce heat. 9- Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has

Use only QSC’s M10 forged shoulder eye bolts. Contact QSC Technical Services department for complete information. Cooling This is a self-powered loudspeaker containing an internal power amplifier that produces heat. Allow a minimum of 6” (152mm) clearance at cabinet back for convection cooling. Keep anything that might restrict airflow away from the rear of the enclosure (i.e draperies, fabric, etc...). Do not use the HPR152i, HPR153i, HPR151i, or HPR181i oriented horizontally. Horizontal orient

NO USER-SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED PERSONNEL. The lightning flash with arrowhead symbol within an equilateral triangle is intended to alert the user to the presence of uninsulated “dangerous” voltage within the product's enclosure that may be of sufficient magnitude to constitute a risk of electric shock to humans. The exclamation point within an equilateral triangle is intended to alert the user to the presence of important operating and maintenance (servicing) instr

Polarity can be altered by miswired input cables, interconnecting cables, mixer polarity switches set incorrectly, just to name a few likely culprits. To make matters a bit more complicated, phasing is also influenced by the position of loudspeakers with respect to one another and by their position in a given room. It is possible to have all loudspeakers polarized properly (electrically) and yet achieve better bass response by having the subwoofer reverse polarized. It is even possible to achiev