My Fishman SA220 has very little volumn on the left input and the red clip light is permanently on

If it's the same as mine, the tuner has a little clothespin clip. You clip that on to your guitar's headstock and turn it around till you can see the screen while picking strings. The tuner picks up vibrations through the headstock and with it's microphone and it tells you what it hears. The little needle tells you the note and if the string you're plucking is below that note, above that note or right on. You have to figure out if you're in the right octave on your own.

That light is showing that there is power to amp in that speaker but there is something wrong with the amp or the speaker inside and nothing is coming out. You will have to troubleshoot the amp and check the resistance of the speaker to see what the problem is.

http://www.mydukkan.com/media/2006_CEC-5_Schematics.pdf
try that friend.

This is an indication of an internal component failure. The unit needs to be sent in for service. It requires special tools and skill to service.

I have seen defective XLR cables so check it with an ohmmeter. It is possible the mic input preamp has been damaged. If that is the case, the unit will have to be repaired.

The fuse is inside and if it blows, there is something wrong that caused the failure and MUST be repaired as just changing the fuse MAY do additional damage.

It is available here:
http://www.fishman.com/files/sa220_user_guide.pdf

Good luck, and I hope this helps!

If you have a pedal input, you may be getting FALSE trips of this.

You may have a pedal jack with switch that is marginal.

TRY putting a pedal into the effect pedal input IF your unit has that and SEE if it acts stable.

These jack and jack switch problems are a pain on all these amps... any brand.

Check the battery in the preamp. Also adjust the eq to see if you might be clipping the frequency you are generating.

ALSO do not overdrive a tuner... they get confused and won't register.