Behringer BX3000T start, shutdown problem

[retgaz]

I have a customers Behringer BX3000T bass amp in for repair.
After a gig the amplifier suffered a fall of about 6ft. The amp wouldn’t work at all after this.
Inside the amp I found the fuse holder on the power amp board was broken, I replaced this. I then checked for dry/suspect joints or any other damage, re-soldering as I went.
The amp now works perfectly when it starts.
The problem is 3 times out of 10 the amp won’t start until the volume is wound right up. This can be done using the guitar volume, gain control or master volume.
At switch off, the amp thuds and then squeals. This happens even with gain and master volume off. This didn’t happen before the accident so I’m guessing there is damage to the protection circuit (does this amp have soft start?).
I know I’ve got no chance of getting a Behringer schematic. So I’m hoping that somebody can suggest possible causes of this fault, or components to test around (all components are numbered).
I’ve tried to trace things through myself but on the double sided boards with surface mount components and many tracks obscured from view, I’m struggling.

[J M Fahey]

It probably has a speaker muting relay.
Being a mechanical device it might be physically damaged by the fall.
(OK, not *the fall*; rather the end of it)
I guess replacing it might restore things to normal.
Another possibility is that it cracked solder pads of tracks, again because of its weight.

[Enzo]

No relay.

Check your patch jacks. Is signal present at FX send? Line out? Does a cord from FX send to FX return help?

[retgaz]

As sods/murphys law dictates the start up problem hasn't happened again since I sent my first post. I don't believe that it has magicaly cured itself but I can't trace that fault until it returns.
One thing I should have mentioned in my first post is that the level meter on the front of the amp shows a signal even when no sound is audible.
I've got my signal generator and scope ready for action. But without the fault returning I've nothing to chase and without a schematic it's hard to identify anything but the obvious parts of the circuit.

With regard to the loud noise at switch off. I checked the patch jacks for intermittent connection and to see if plugging into the return jack would stop the noise (assuming I was bypassing the pre amp). The master volume controlled the level of the guitar I had plugged in. With the master volume set to off I switched the amp off, the noise happened again followed quickly by the guitar coming through the amp for about ten seconds.
This may mean nothing, but as mentioned in the first post the amp was totaly silent at switch off before the fall, so I know something is wrong.

[knutknut]

Does any one have a schematic for this amp. I have one with a problem on the power board, and a schematic is needed to work out what is going on