On u47 a=cl +mod b=od on the screen the sound comes out one headphone speaker a lot more louder than the other all the leads are ok the headphones are ok and the balance is set in the middle is this normal thanks

If you can get sound from the headphones, it may be that you need to have that jack replaced- there's a cutout on a headphone jack so that the sound to your speakers is off when headphones are in use. If you cannot get sound from either the headphones or speakers, it's probably an amplifier problem- which needs a tech. Is it under warranty?

Suspected Faulty PC board Dead Capacitor Or Mod Pot I would suggest returning it for an exchange the problem is your speaker will work on a regular stereo because a stereo powers the sound internally causing the magnets in the speaker to vibrate Headphone jacks are designed to pick up off a seperate circuit board with a different connection to the main board hence the no sound from the speaker.

A common problem is that the switch contacts on the headphone jack that send the audio to the speaker when headphones are unplugged go bad. Some of these are so low quality that after a few times of inserting a plug the contacts no longer make. If you can access the jack, you might find a jack similar to: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RA49B12B-ND
What happens is the spring tension on the tabs over the top of this that contact the leads to the speaker lose tension and no longer press hard enough on the contacts to make contact. Try to open your unit and see if it has this kind of jack... Frankly, these jacks are JUNK and a chronic problem.

I have a 250 gfx, and I have had the same problem intermittently, I have concluded that the digital fx section is to blame, as it is also responsible for the speaker modelling for the line/headphone jack, and I have also had problems with my fx section.
If you have anything in the effects loop that boosts signal volume remove it, a small boost in the loop gives the power amp in these a nice glassy sound, but seems to be (in my case at least) responsible for the failure of the fx/ emulated line out.
Also check all your leads and headphones cord, try some different headphones if you have them.

Clean the head phone jack. When you put in headphones, they mute speakers. If headphone jack is dirty or stuck, speakers remain muted.

First verify that one channel is bad by swapping the output leads and seeing the bad audio comes from the other speaker. Assuming it does, you probably have a bad output driver on one side.
This can happen if one powers part of the system from different receptacles in a venue and electrical disturbances destroy one or more audio interconnects. ALWAYS power ALL interconnected equipment from the same source, even if you have to run an extension cord between power amps and the mixer.
You will probably need to take the unit for repair. The parts cost should be nominal, however labor could cost a bit.
Find out is SAME distortion is present in the headphone output. The circuitry shows a bunch of muting transistors and one of them could be bad... but we can do some troubleshooting externally with testing at headphone jack, etc.

The bypass switch in the headphone jack is likely broken. NEVER unplug the headphones while the amp is on.

There are certain small amps that have a possibilty of popping the power amp due to a feedback arrangement. Likewise, never use the headphone jack for ANYTHING other than headphones.

Inside the headphone jack is a built in switching mechanism. It is there to cut off the sound to the speaker when you are using headphones to practice quietly. For some reason or another it seems as if this is no longer working correctly. One of the causes of this can be bad solder joints on the circuit board where this jack is located. Another cause is a failure of the jack itself. If you are capable, Take the circuit board out and have a look. Hope this helps.

When it was knocked over it may have cracked the main circuit board, but does the pilot light come on at all? If the pilot light comes on but no sound is output from the speaker try plugging some headphones into the head phone jack and then turn it on and see if you can hear sound in the headphones. I have had a similar problem before and the main speaker had gone bad but it would still play thru the head phone jack.