Mackie Studio Monitors HR624 MK1 – no power or wont stay on.
These great little monitors suffer from a regular power failure problem where they will not turn on. Not always, but quite often, this is actually a fault with the standby circuit which shuts the amp off as it thinks the input signal is too low. 
The solution is remarkably simple and just involves the replacement of a few capacitors. If you think you might be affected by this issue get in touch as amp repair is less than you think. Individual amps cost 1.5 hours time and a pair can be done for 2.5 hours + postage.
Best thing is to remove the amp from the cabinet by undoing the 8 torx screws on the back and packing the amp up and sending it in to me.
Hi, I’m having this exact problem. I’ve replaced all three of the capacitors in the area of the standby circuit (1x 4.7uF, 2 x 47uF), but it still doesn’t come on. It is switched to ‘Power on’ mode on the back, so not using ‘Auto’ mode. Fuses are good. Not sure what to replace next. Would greatly appreciate your advice.
Hi there I am afraid it sounds like your speaker has a deeper fault. If you are able to do so safely, I would recommend checking all the power rails are correct as that is a good start point. Also beware, one of the big problems with powered monitors is the use of black goopy everywhere to prevent internal resonances. This stuff is somewhat corrosive to the PCB and often makes repair impossible to achieve especially when the unit is 10+ years old or so. Good luck getting a fix.