Turns on, then shuts off, then turns on, then shuts off and so on

1. Make sure nothing is plugged in.
2. Turn the GAIN, LEVEL, and FX knobs for each channel, counter-clockwise all the way.
3. Bring the MAIN fader all the way down.

If the signal LED's above the MAIN fader are still lit, then the board most likely has a short in it and will require repair.

If the signal LED's are dark, repeat the following on each channel...

1. Rotate GAIN clockwise until the mark on the knob is at "12 oclock".
2. Rotate LEVEL clockwise until the mark on the knob is at "3 oclock"
3. Raise the MAIN fader to "0".
4. Check LED's - if they light up then the channel you are working on is "noisy" or has a short in it.
5. Return GAIN, LEVEL, and MAIN to "all off".
6. Repeat with next channel.

Check the burned out LEDS with a 3 volt battery- a computer bios battery works well for these.

If they do not light, which is likely, just replace them with similar sized units. You can even change their color too. Measure the voltage at the LED sodler pads to see if it is more than 3 volts, if it is, add a resistor to drop the voltage and limit current to the replacements. Digikey sells them, and they ship around the world http://www.digikey.com or Mouser, Both are based in the US, I am not sure what Mouser's international shipping is. http://www.mouser.com

If there is no voltage at the LED pads, look for bad solder connections, or burned out resistors. If the few remaining LEDs still operate as they should, the level meter chip "should" be okay.

USUALLY the Mute LED's for the switches ar operated by separate contacts on the mute switch an a resistor current limit for the LED. I could NOT find the schematic for this board, HOWEVER some Soundcraft brand mixers do NOT have illuminated Mute switches... Not sure about your particular unit.

Are you Pushing the system over its limits by Peaking everything. Sometimes they auto Shut off if your pushing to hard.

Hello!
I am not positive on this but I would try to clear all of the loops. Try holding the right pedal for about 5 seconds.
If that does not work, hold the right pedal for about seconds while you turn off the unit. Release the right pedal then turn the unit back on.
Hope that helps!

Best to leave the limiter on unless you want to blow the amp and require repairs. Limiters protect the amp and also sometimes the speakers. The limiters reduce the gain when the amp reaches the maximum swing. If the gain were not reduced the amp would "flattop" which results in the circuitry saturating and massive distortion and if this condition is sustained, components can overheat or short out requiring repair. The LED MAY be just an indicator of clipping rather than an indicator of on/off. I downloaded the manual and what I have just said is CORRECT. The LED is a clipping indicator.

There is a caution regarding this amp and the sequence to turn power on. This amp does NOT have good speaker protection and you have to have the gain control down when turning on. The limiter, if you leave it on, might help protect your speakers when powering on. Most good power amps have circuitry to disconnect the speakers while amplifier is powering up and becoming stable, this one does not, so heed the warning and for certain leave the limiter ON... It just might save the amp and your speakers.

Before turning the unit on, press and hold down the calib/batt switch to check the condition of the battery on the battery meter.

Then either plug in your electric guitar to the input side of the AG-6 or if tuning an acoustic guitar without electronics placing the AG-6 near the front of the guitar should work. You will not need to press a button to select which string you are about to tune. The AG-6 will detect it and the corresponding light will turn on when it is tuned within range.

Turn on the AG-6 and start by striking the low E (thickest) string while open. This is the number 6 string or 6E. Slowly turn the guitars low E tuning key untill the red LED below the 6E marking on the AG-6 lights up. Continue stricking the open string and turning the key untill the needle centers on zero and the 6E light remains on.

Repeat this for the open A string untill the 5A light turns on and the needle centers on zero.

Repeat for the remaining four strings, 4D 3G 2B and 1E, being careful not to over tighten and break them.

Tip: It may be a good idea once the low E string is tuned, to tune the rest manually, especially new strings or strings way out of tune. Then tune again using the AG-6 tuner.
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If installing fresh strings you will probably need to stretch each string and re-tune, possibly several times, before they hold their tuning.

I have found a site with SWR schematics: They have one for the SM400 which may be very close to what you have, or at least parts may be the same.

http://www.freeinfosociety.com/electronics/schempage.php?cat=1

The circuitry is a bit complex for that PFL light. The LED is driven by a transistor T38 type BC846 to turn it OFF by grounding out the current coming by way of teh MUTE LED or the MUTE switch (SW14) horts out the MUTE LED. There is a 1K limiting resistor from +15 volts feeding the two LEDS in series.

IF transistor T38 is open the PFL will be on. HOWEVER T38 will also be turned off if transistor T44 (BC846 type NPN) or if capcitor C90 2ufd/50v is shorted OR if resistor R253 is open OR is switch SW8 (PFL DPST )is not contacting the ground side of of the half tied to R247. If R247 is open that will also cause the PFL LED to illuminate...

AND if the signal coming in is at clippling level the PFL LED will light.

All that circuitry serves as a clip detector plus the PFL function.

Verify you are not sending clipping level into the channel first... turn the trim off. If not, you are in for major surgery as all the knobs for that section of the circuit board and the screws for the XLR's and the 1/4 inch jacks must come off as well as some support screws IF it is necessary to access the top side of the board... Maybe you will get lucky and the bad component MIGHT be on the bottom of the board.

If you are using battery power, just because the LED lights doesn't mean the battery is adequate. Check the battery voltage.

If you are on adapter power, make sure any bypass switch is in right state. Also occassionally someone gets the in's and out's cables backward... that can do it!