Active PA Speaker ( built in power amp )

[Guest]

Hey all.. I figured I would ask here since all of you seem very knowledgable..

I picked up an active PA speaker, it is a PA speaker with a built in 400 watt amp..

I got the thing cheap and it was new in box... well low and behold, there is something wrong with it...

it sounds great but it gets EXTREMELY HOT on the heatsync, it also makes a strange muffled humming noise that sounds kind of like when someone is outside mowing the lawn.. That said.. I gave the thing a SMACK on the heatsync, and the noise stopped and I powered it down... I let it cool a few hours and went and turned it on before and now.. no strange noise and its not heating up... been on for a while now and it is functioning perfectly.... as a test, I powered it down and moved it around... put it on the floor, rocked it around etc... turn it on and problem is back, noise starting and heating up... gave it a quick smack and noise stops and it cools off....

now I am not techie.. I have no idea what I am looking at under the hood if I took this apart... Is it safe to say, I might be able to take this to someone who repairs electronics and they might simply find a loose component inside or something?? I am trying to keep this as low cost as possible...

This item is a CRATE PSM12P Active PA speaker...
any thoughts or suggestions?

[Pentode]

Sounds like thermal run away.... usually due to leaky driver, power transistors or their biasing components and sometimes faulty chips.

Noted you say you gave it a quick smack and it stops it, this sounds like a bad soldered joint in the power amplifier section that simply wants re soldering and seems to indicate the fault is of intermittent nature.

Rather than smack it, run it out the box and carefully tap each component in turn when the fault appears using the handle of a screwdriver.... be careful not to short anything out of course.

Dave