Can hardly hear it,seems like it's running @ half power.

i suggest you contact Behringer Customer Service for advixce. Without the setup in front of me, it's hard to figure out the wire routeing, switch positions, ect. that may be leading to this problem. As they would be the people most familiar with the gear, they'sd be the people to ask. http://www.music-group.com/support/behringer/askquestion

How do you know it is going half power? did you measure this, or do you only hear half the power? because then also a speaker (or more) could be not working.

sounds like out put transister
or power overload

Does the left meter do the same thing? If the meter matches the right one, I would suspect the volume potentiometer on the powered speaker. Try exercising the volume knob. There might be some oxidizing on the potentiometer.

This unit has a TDA8920 dual switching class "D" switching amp chip that is thermally protected. If you heat it up it will shut down to protect against overheating. Each side of this is ONLY a 50 watt amp chip HOWEVER they run it at a lower than rated voltage that limits it to about 30 watts per side. Your dial setting number have NOTHING to do with the power limits of the unit. When you use the looper, there are more frequency components added, and all these consume part of the available power. Also make sure the mics and the guitars cannot "hear" the speakers in this otherwise high frequency feedback may occur above what you can hear and use some of the capabilty... hint... reduce the treble boost... The only way to measure the power output is to put a scope or test equipment on the output and compute the power. I suspect you are driving the unit too hard. The unit should give adequate output for a 15 foot square room to a level that *********** could just barely tolerate. Yes, the power amp chip is thermally protected and if you drive it to hard it backs the power down till it cools off.

It is very hard to determine what you mean by "When replacing the power supply"... do you mean replacing the battery? Or the whole preamp? Without knowing your whole system it is hard to analyze the noise source or what is the nature of the noise, If you have a hum problem or static, I would check the quality of your audio cable. A high quality instrument cable must be used. Lamp dimmers can create noise... I need to know the nature of the noise you are hearing.

The hard drive has probably failed. In spite of it rotating, the head servo and electronics has to work. I would recommend testing the drive in a computer to see if it works. You will likely have to reformat it after if it does work. FIRST look for obvious things in the D888 like cable that is partially off or loose.

You should NOT be blowing fuses... If you are you MAY be overdriving the amplifier. It should be hard to blow fuses in a tube amp unless the power tubes have become gassy (purple glow between the elements) or you are driving a square wave (full distortion) that may be saturating the output transformer.

This unit has a digital signal processor for the modeling and when the amp seems to freeze, it is probably this part of the system that freezes and ceases to pass the audio.

Make sure you run the amp on CLEAN power. Using a long small gauge extension cord may cause the freezes.

An even more insidious problem is static electric discharges... some so small you may not even feel it. If you are on rug, spray the area with Staticide anti-static spray. A small static discharge can send the DSP into never-never land and the amp will appear to quit. Raise the humidity to at least 40% will help the static problem.

Make sure you are using grounded outlets.

Please note that the outputs of the MAIN L/R line outs are TRS balanced. If you plug mono plugs into these or connect to mono device you MAY have a problem of grounding out half of the drive internally. ALSO please read my tip on here regarding a polarity hazard of speaker cables of PMP amps if you do NOT have Speakon to Speakon cables, but have Speakon to 1/4 inch cables.

Likely one of the power amps in this has failed If no lights come on the unit now, then the power supply is wiped out as well. It takes about $50 worth of parts and quite a bit of skill and work to restore the unit, including carving out burned board and re-insulating. Likely a feedback occured on that mic and started the whole thing. Supersonic feedback is something most musicians are NOT aware of, but if the feedback is above the range of hearing, the amps can be strained as they may go to maximum power trying to amplify the sound you can;;t even hear. Piezo tweeters are capable of frequencies up to 30KHz.

If this is under warranty exercise it immediately.

First thing is to open the unit and make sure the drive is connected. Sometimes cables get knocked off.

Next get a new drive... they are relatively inexpensive, like $69 or so and try it.

Take the old drive in your hand and snap your wrist to impart a spin to it. Then try the drive again... If it comes back to life, SAVE ALL THE DATA from it quick, and transfer to the new drive.