7-band fader LEDs not working and no sound from speaker. Any internal fuses? Pre-amp board fault? Any pointers appreciated.

It's always possible, but I doubt it's the fader. I'd suggest taking it to the shop for a hands on diagnosis.

The "PFL" Stands fo r"Pre Fader Level". Just in case you did not realize. so when you press the "PFL" button , and the red light goes out?, You're saying that the hissing goes away and that you have clarity. Yes? and the volume presents no issues? Also correct? Part of that simply, is with the PFL in the on position. You are engaging the fader for one, which will add to an already boosted signal ( the the fader is turned Up?). also you may have your Clip set incorrectly. to set this you turn PFL off, then at your signal input level Dial (usually at the very top in-line with your fader. _ set the volume on your device, then input clip level on the board \ to where the clip light comes on. not a steady light, but a blinking light so make it steady, then back it off a hair. Okay? this whole time make sure your mains are down. or off at the faders. Once clip is set., PFL is in off position, gradually turn your mains up to level. Now, the PFL is for when you have more than one signal. say from an instrument on another channel. unless you have that? No need to use the PFL. If you do have an instrument in line,. then, before you turn PFL on,make sure that your fader on that channel is turned off. -turn on your PFL, then gradually bring that to level. never messing with the mains level.

I know that is a lot of info. but it is a process. that should eliminate any hissing you may have heard.
Good luck!!
'

Of course I can't be sure but most amps don't have fuses on the circuit boards anymore. They use protect circuits, they may have blown your amp and yes it could be expensive. Are there indicators on the front panel? LEDs on that shouldn't be?

It appears that AUX6 is default factory strapped as POST FADER. If you want to change that you will have to disconnect jumper L to A for all channels you want the AUX to be pre-fader and instead connect K to S for the option jumpers. I don't know if this requires soldering or whether they are push on jumpers. These should be available in the back cover. In ADDITION you will have to run the switched pre/post fader switch in the PRE position which will make ALL AUX's that are strapped this way PRE FADER.

There can be any number of reasons for this problem - solve it diagnostically by starting with something that you know is working and work through systematically to the other end.

1. Test a microphone on a separate amp to make sure it works okay. Check amp and speakers working. Check that all output cables from mixer to amp are working by testing separately.
2. Plug microphone into a channel on mixer. Also plug in headphones and turn headphone volume control up.
3. Make sure input sensitivity knob is turned up a bit (say half way) and main output faders (yellow) are up.
4. Check that channel is turned on (little button just above the channel fader- needs to be pressed down)
5. press pfl (pre-fade listen) button (next to button to switch channel on)- do you get any sound on main output or headphones or any indicator lights on mixer to show signal is getting that far (eitehr the individual channel metering lights or the main ones in the central section)?
6. turn off pfl - make sure channel fader (slider) is up - normal position is ) - about 3/4 of way up. Check lights again on individual channel and main output section - any signs?
7. Is the sub mix button for the channel pressed down - in which case you will need to bring sub mix (red) output faders up as well as main faders.
8. If you have got signs of signal on the individual channel but not main see if the channel has been routed somewhere odd (like a subgroup of channels).
9. Plug a working amp and speakers into one of the auxiliary outputs and use the relevant auxiliary send knob (on each channel just above the faders and pfl switches) to pan some signal to that auxiliary out - do you get anything? There is also a headphone socket for listening to the auxiliary channels (with a selector switch /knob to determine which one - make sure it is in the right position) try listening to the auxiliary output with headphones - anything? If yes the problem lies in the main output section.
10. Check that there is not a jack plug in the insert socket (to route signal through an external effects unit) without a matching return jack being plugged in - if appropriate is relevant effects unit switched on and correctly set up - if unsure remove the insert plug to take it out of the system.
11. Make sure any mute buttons are not switched in on main outputs.

You can download a full user manual here http://www.allen-heath.com/gl/gl2400

The MON faders ONLY control the output to the MON L and MON R jacks, NOT the split use of MAIN/MON outputs. You MIGHT try varying the MONO fader and see if it varies the MON part of the split output.
Best to use the unit as MAIN L and R to main speakers and use a stereo amp or POWERED monitors driven from the MON L and R jacks. With this, the MON faders will control your monitors as you would like them to.
ALSO make sure ALL equipment connected together is powered from teh same recepacle power system. Powering interconnected equipment from receptacles at opposite ends of the room is asking for damage due to ground bounce and faults.
PLEASE read my tip on here about a HAZARD of speaker polarity if you use Speakon to 1/4 inch cables.

Since the pilot light is on, the transformer is delivering the heater power.

An educated guess at the problem is a crack on the circuit board or bad solder joint. Since NONE of the EL84's are lit, there is likely a crack or soldering at a circuit board feed-thru.

Should be easy to trace. PLEASE be careful as there is around 400 volts in this amp !!!!!

This often normal to get a pop as the power goes down. The amplifier goes out of balance as the power drops and it drives current into the speakers. This is a design problem and most amps don't even TRY to avoid it. Very large amps have relays that disconnect the speakers an instant before the power collapses to protect the speakers.

check for cold solder joints from the input jacks and the fader. If any look suspicious (dull or grainy) re-solder.

Send main 1 out to your Crown. Jump Mon send to PWR am insert.