The top part of the mackie speaker isnt working. all that is working is the big bottom part, and the sound sounds like the bass is the only thing coming out.

"How to replace bass driver in mackie thump 15a".
Did you mean,disassembly the speaker enclosure?
Just remove the 16 screws at the rear cabinet, using a screwdriver.
Then remove the 4 screws that secure the speaker, using the hex key. Is the bass driver blown up / broke?

Could be the crossover has died or the main speaker winding has failed. Open her up and connect on side of the main speaker direct to a 9v battery and then wipe the other wire over the other terminal. If you get a crackling from the speaker then it's likely the crossover, if there is no response at all from the speaker then it is dead and possibly the crossover too.

Sound like either the crossover or the driver has blown or, if you're lucky there is a loose connection internally if you have only checked external connections.

It would be very unusual if the blue LED is burned out. They should last a million years. I suspect the power supply has a problem.

realistically, I would say they've had their time, and it would not be worth repairing. it could be more than just the speaker that blew, parts for desktop speaker systems are almost nonexistant unless you know you're way around jury-rigging electronics. Plus, there are quite a few new sets out there that would be superior to what the ACS400 puts out, for decent pricings.
I myself am a big advocate of the Logitech THX-certified product lines- they have excellent bass, crystal clear sound, and are great value for the money.

The amplifier takes a bit of time to come to DC balance and same thing happens as power goes down. Some fancier units will have a relay to disable speaker until balance occurs, but this one does not. As long as the cone centers within a couple seconds it will not cause a long term problem.

does your swa1501 get hot just being switched on ?
sounds like your output transistors breaking down or your dc to dc rectifier is shorting this would dumping high voltage to the speaker. I guess your speaker coil is burnt . check Q4,Q5,Q7,Q12.Q14,Q15,Q17 and Q18 these are all mosfet transistors that commonly break down..

Hi There, This is quite a common problem with the Mackie SRM450's. You will find that you need to replace the diaphram on the top. This can be done by removing the 16 screws from the back of the Mackie (quite a long pain in the **** job) with a long handled cross head screw driver.

Once you have done this you should then remove the hex bolts from the back of the drive where the black and right terminals are. When this is done, pull off the cover and swap the diaphram out. With the new diaphram in place reverse the steps above but before you screw the back on, power it up carefully and check the sound is now working.

If the diaphram keeps going eg every 3 to 4 months then you will need to change the driver which is quite expensive to do. If you need spares and are based in the UK, contact LondonSpeakerShop.com who carry spare parts or can undertake the repair.

Hope this helps.

you have one of two problems.1) the woofer is blown(most likely) or 2) the crossover is fried(rare). Take the woofer out and press on the speaker cone(softly). If there is a scratchy feeling when you move it or if it doesn't move at all, you'll either need a new woofer, or get that one reconed.
good luck.

get a bass amplifier and connect to the subwoofer.