MPA685 Owner’s Manual
3/2012
17
TROUBLESHOOTING
1. Power does not turn on
Verify that the rear panel master AC switch, if present on your option, is turned on. Check
the AC fuse. The fuse holder can be removed when AC power is unplugged from the unit.
Use a flat blade screwdriver to remove the fuse holder from the unit. Use only a 500mA
slow blow fuse.
It is possible that the power is still on but the Power-on bulb is burned out. See the next
section on replacing the Power-on bulb.
2. Power-on Bulb Does Not Light
Verify that the pre-amp power is actually on and audio is being amplified and applied to the
output. If this is the case, the bulb may be burned out. Unscrew the lens cap from the light
assembly and remove the bulb by pushing the bulb in and turning to the left. Replace the
bulb with the type listed in the Specifications section.
3. Microphone Input Audio Sounds Distorted
Decrease the step switch position by one increment. If the audio is still distorted, decrease
the step position one more increment. If the audio is still distorted, change the input
impedance (if using the balanced microphone input).
4. Direct Instrument Input Audio is Distorted
Remove the loop-through connection, if a loop-through is connected. Retest the audio
quality with only the instrument connected to the pre-amp and the DI loop-through left open
circuit.
Decrease the step switch position by one increment. If the audio is still distorted, decrease
the step position one more increment.
If the audio quality is still degraded, check the integrity of the audio cable connecting the
instrument to the pre-amp.
