Very low output

First - Check the connections on the speaker itself - when speakers don't work. it's usually the wires from the power amp section to the speaker. If those are OK, try replacing or bypassing the headphone jack - you may have a short in the output jack. Good Luck

If everything lights up and responds to button pushes like normal, and you've done a hard reset as described in the manual, check to see if you have sound out of the headphone jack. It's most likely not a user serviceable problem and will need to go to the shop, but it will probably be the output amp rather than the main board.

Check to make sure the problem is not with the headphone jack or the external speaker jack as these are in the circuit between the power amp chip and the built in speaker.

You can also trace through the circuit with a music source on the amp input and with simple headphones check the signal path through the circuit until the music disappears. To do this, take a headphone and set it up with 2 test leads on the ends- attach one to ground.

Now your TL072 op amps have 2 outputs, pin1 and pin 7. The inputs for pin 1 are pins 2 and 3, and the inputs for the amp section outputing on pin 7 are pin 5 and pin 6. If you get sound at pin 1 or pin 7, you move forward to the next TL072. Check for output. Then move to the power amp chip on the heat sink. Pin 1 should be the output and will be wired to the headphone jack first. The external speaker jack second and the built in speaker third. The input for that power amplifier chip is pin 7 or pin 8 depending how it is wired.

If the amp chip is blown, make sure to put an adequate amount of thermal grease on the back side of the IC in contact with the heat sink so it can operate as cool as possible.

Do some tests: Plug a set of headphones into the line outs and tell us which ones if any have sound. Note that only one side of the headphones may have sound and it may be low volume. We need to know if anything is coming fromt he preamp. Makesure the output switch is set to one of the speaker on positions and not just phones.

I first would suspect the switches on the eadphone jack. Normally these cut off the speakers when headphones are plugged in. These jacks and the switches are really weak, poorly made, and easily broken, especially if headphone cord gets yanked.

Check if headphone output is normal... sometimes the headphone jack switch fails and doesn't send to speakers when headphones are unplugged.

Contrary to what's posted above, the Marshall MG series does not pass the speaker power output through the headphone jack, and inserting the headphones into the jack does not disable the speaker. The headphone amp is a separate circuit and it's input is taken before the master volume. So Jan's post is exactly right. Turn off the master volume and turn up all the other gain/volumes as high as they will go. The other issue is that the headphone jack's output does not drive low efficiency headphones well, so you need some headphones similar to Sony's MDR-V700s to hear it well. Earbuds just don't cut it.

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.

There are some possibilities. One, your speaker may be blown or disconnected. Make sure the wiring is still connected to the speaker and if you have one, try measuring the resistance(impedance) of the speaker with a volt ohm meter.Do this unplugged from current and disconnect one of the wires from the speaker or you will get a reading from the output stage. Two if there is a heaphone or line out jack it may have become faulty. If you have sound with the headphones plugged in your amp is still producing sound. Some jacks are designed to interrupt the signal to the speakers allowing you to practice without bothering anyone. If your amp has that feature and you still have sound with the headphones and your speaker tests OK then your problem is the jack. Hope this helps.

Probably the easiest way would be to use a stereo receiver. You can run the headphone output of your ipod into a tape or cd input. The only thing to deal with will be adapting a stereo 1/8" (3.5mm) headphone type jack to 2 RCA type input jacks. You should be able to get this cord at radio shack. You might also be able to purchase a receiver that has a 1/8" input jack specifically for connecting things like an ipod. A receiver, by definition, has a tuner built into it. The alternative would be a tuner and an 'integrated amplifier' which has power amps to drive speakers as well as a pre-amp and input selection switching.