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Knowledge Base > Discontinued Products > 571 SPL Computer

Why does the SENSE INPUT ERROR LED continue to flash at the end of the 571 SPL Computer calibration process?

The SENSE INPUT ERROR LED flashes at the end of a calibration attempt to indicate that the 571 is not receiving ambient level information on either the SENSE MIC 1 or SENSE MIC 2 inputs. If this happens, your calibration attempt was unsuccessful. Make sure that the SENSE 1 trimpot and the SENSE 2 trimpot(if used) are turned clockwise. If this trimpot is turned part of the way to the full clockwise position, and the SENSE INPUT ERROR LED flashes when you attempt a calibration, try turning the SENSE 1 AND SENSE 2 trimpots completely clockwise.

Check your mic cables, and make sure that a sense mic is actually plugged in to each sense mic cable. If your sense mics have ON/OFF switches, make sure that these are in the “ON” position. Current revision 571’s have phantom power on all mic inputs, but 571’s manufactured prior to early 1996 do not have phantom power, so you will need external power supplies for condenser mics used with pre-1996 571’s. Do not use an unbalanced mic with the 571. These mics usually short XLR pin 3 (“RING” on a 1/4 ” connector) to ground. If you connected one of these to a mic input on a current revision 571, you would be shorting the phantom power supply to ground. Also, an unbalanced mic line is far more likely than a balanced line to pick up noise, RF, etc. You can check your sense mic and mic cable by unplugging the cable from the 571’s SENSE MIC 1 or SENSE MIC 2 input, plugging the cable into a mic pre-amp, and listening to the output of the pre-amp with headphones. Be sure to reconnect the sense mic cable to the 571 afterwards!

You can also view the SENSE MIC inputs using the built-in factory test for the 571. To get into test mode, hold in the 571’s MODE switch for about 10 seconds, until the far left GAIN (dB) LED begins to flash. You are now in “Sense View” mode, and the GAIN (dB) LED’s will indicate the level of the ambient signal being picked up by the sense mics. If no LED’s light in this mode, try turning the Sense Mictrimpots completely clockwise. To return to “Operate” mode, power down the 571 and turn it back on.

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