Where can I find a repair manual for my Mackie Thump 15a powered speakers?

SOURCE: Have a Mackie 1604 VLZ

One of the power supplies has failed. This can either because of a short on it or the regulator chip has failed. Unplug the power cable from the main board. At one end are the +/- 16 volt supplies with ground in the middle. and the other end has a ground and the 48 volt phantom power. There are a couple grounds near the middle and a 10 volt power as well.

Here is your schematic:

http://elektrotanya.com/mackie_1604vlz.pdf/download.html

Scroll down to "get manual" and click on it to download. IGNORE other download links... they are for third party PDF readers.

The order to troubleshoot: Unplug the power cable from the supply to the main board. Test for those voltages with power on. If they are NOT there, disassemble the pod to get to the power supply and troubleshoot for the missing +/-16 volt supply... May be shorted by
a cap or the regulator chip may have failed. If the supply voltages are there, turn off power and replace the connector being VERY careful to not get it a pin sideways as there is NO index. Next disconnect the audio cables to the pod and reach in and check the voltages on those pins again on the power cable, or just note if the LED's are still screwed up... If they are, congratulations... you get to remove the POD from the back.... 4 screws... and then get to carefully pull every knob off the panel and using a small hex allen wrench remove a bunch of screws to release the main board. There is a dust cover for the faders... remove this noting the oreintation and DO NOT forget to replace it when you are done. Now you can reconnect the power supply to the bare board. First thing is to visually inspect for the obvious... next with power on use a "calibrated finger" to look fo a hot chip that might be sucking the current... beyond that you use the techniques of millivoltmeter searching for where the current is shorted looking for the place where that voltage goes to near zero. This uses the resistance of the power buss. When it is all repaired you get to put those knobs back on... been there, done this... I had a bad chip that was the driver for the MAIN INSERT... stuck down between the main fader and the one next to it. ALWAYS power all interconnected equipment form the SAME receptacle or power conditioner to avoid the ground bounce damage like this.

SOURCE: Bought a used Mackie TH-15A.

The internal amp is in need of repair. Are there any other symptoms or signs?

SOURCE: i have a mackie fx 8 mixer connected to two thump

Balanced audio interconnects (either XLR or TRS cables from the mixer and then balanced audio interconnects from the amp daisy chain inputs to the existing speaker inputs. If the amps do not have linked input jacks, then use TRS type WYE connectors at the inputs. Then use speaker rated cables from the amps to the passive speakers.