All the lights are flashing on my Mackie prO fx8 What is causing this? I've not this second plugged anything into it - will it still work - all instruments speakers etc at another location...

First, unless you are a trained or self-taught audio technician, don't attempt to repair the unit yourself. Let the professionals repair it. You can damage it beyond repair if you don't know what you're doing.

Non-working channels are caused either by bad connections, bad solder joints or a dead IC op-amp.

The causes of weak channels can be more challenging to track down. I'd suspect bad connections, dirty controls or connectors.

It's probably not getting power to the lamp connector. Get a voltmeter and check it.

Your best bet is to contact Mackie Tech Support. Here is a link to their Suppot page. Mackie Tech Support
it's likely it needs to go to a repair shop. Here is a link to their service center finder. Mackie Service Center Locater

Probably the power inside the mixer needs to be looked at.

Are you sure the xlry cable is balanced? there are balanced and unbalanced xlrs. For phantom to work, you need a balanced xlr cable.

Do the protect lights light up when you turn it on? There is a soft start circuit that should delay for about 3 seconds when powering it up, it sounds as if this is not working. If you don't get the protect lights for a second or so when turning it on then this has failed and you need to get it serviced and repaired before more goes wrong.

Make sure you are using BALANCED audio interconnect cables AND that the speakers and the mixer are powered from the SAME receptacle... Yes, this means running extension cords. It is a ground loop problem. You should be using XLR or TRS cables BALANCED cables from the mixer to the basss unit of the L1 system. The bass unit and the mixer MUST be powered from the same receptacle to avoid ground loops and hum.

This probably means there is a failure and the internal protection circuits have activated. It will probably have to go to a shop for repair.

Mackie does sell parts. If you cannot afford or get the part, procure some metal and make your own. Mackie is headquartered in Woodinville WA I believe.

(800) 898-3211 Monday-Friday, 8am-4pm Pacific Standard Time

same problem here.. gimme a holler if you've figured anything out.
mine, channels light up, it's getting sound (input) from mics, but it's no sound coming out. i'm almost definite the problem is with the main mix slider. but then again i could be wrong.