QSC Audio 1100, 1400, 1700, 1200 owner manual Operational Troubleshooting, 3.92No Sound

3.83Thermal Protection In case of blocked ventilation, improper loading or prolonged short-circuit operation, the temperature of the power transistors can rise to excessive levels. If the temperature of the heat sink rises to 85C, a thermostat will remove power to that channel. Power will be automatically restored when the channel has been allowed to cool down.

Please note that Channel 1 can shut down without affecting channel 2, but if channel 2 shuts down, the muting circuit for both channels will operate and mute channel 1 as well. This was done so that whichever channel might overheat in the bridged-mono mode, it would remove the signal for both channels and prevent damage to the muted channel. The amplifier should come back on within a minute or two.

If thermal problems occur, check for blocked ventilation, proximity to a heat source, short circuit, or improper load (too many speakers).

3.84DC Fault Protection The Model 1100, 1200, and 1400 amplifiers employ a unique Bi-Capacitive output circuit that combines the tight, well controlled audio performance of direct-coupled (DC) designs with the inherent ability to block DC output in the event of amplifier failure. Because this circuit requires dual power supplies, protection is independent on each channel. A DC fault in one channel will not affect operation of the other. Since no relays or other external devices are employed, the amplifiers are free from any false triggering or degradation problems associated with other protection schemes. In the event of an actual fault, DC will be blocked at the output until an internal protection fuse blows. This will remove power from the defective channel until repair can be made. In the unlikely event this should happen, disconnect the inputs and speakers from the defective channel and take the amplifier in for service as soon as possible, to prevent any further damage.

The Model 1700, due to its higher power rating, employs the same dual power supply scheme, but has a more conventional direct coupled (DC) output circuit. It uses a heavy duty Load Grounding™ speaker relay for load protection. This has the advantage of connecting the defective channel’s load to ground for extra protection.

3.85Turn-on/turn-off Muting There will be a three-second muting interval after turn-on. After turn-off, or loss of power for any reason, the amplifier will mute within a quarter of a second.

The outputs of all Series One power amplifiers are DC protected and the circuits have no inherent turn-on or turn- off thumps.

Protective muting for the Model 1100 is handled by a small relay at the input. The signal does not pass through the relay contacts, but is shunted to ground during the muting interval. Thus any degradation of the relay contacts will only affect the muting, and not the audio quality.

The Model 1200, 1400 and 1700 make use of an electronic muting circuit to mute the input of the amplifier. The Model 1700 also makes use of the Load Grounding™ relay to mute the output of the amplifier by grounding the speaker output.

3.86Input/Output Protection Series One amplifier inputs are isolated by 10K resistors, which are part of the balanced- input circuit. This protects the inputs from burn-out due to extremely high input signals or RF interference. The amplifier output is isolated from capacitive and inductive loads by a high frequency RLC network, which decouples the speaker terminals slightly at frequencies above about 50 kHz.

3.87Indicators The green pilot LED indicates AC power, but does not signal status of the muting circuit. After the muting interval is passed, the red clip LED’s will indicate the presence of distortion for each channel. If distortion is heard without clip indication, you should suspect other parts of the system.

3.9 OPERATIONAL TROUBLESHOOTING

3.91Summary This Section contains troubleshooting hints which should help you locate a problem. By using a step- by-step evaluation, by comparing the function of both channels, and by using one channel to check the inputs and outputs of the other, a problem can usually be isolated. Please refer to Section 2.3 for an illustration of the front panel and indicators.

3.92No Sound

Power LED does not come on: There is no AC power. Check AC plug. Depress the AC circuit breaker reset on front of amplifier, next to AC switch. The 1700 features a combination AC Switch/Circuit Breaker— turn it off then back on to reset. Test the wall outlet with another device to check for power.

Power LED comes on: Either the input or output has a bad connection, or the channel is faulty. If one channel is working, use it to test the input and speaker cable from the bad channel. If it still doesn’t work, the fault is somewhere else— the speaker, input source, or cabling. If the good channel works using the bad channel’s cables,

16