Mackie HD 1521 amp module

[Pe7e]

I've got a Mackie HD1521 amp module that's developed a fault, the amp appears to be going into 'protect mode' when played at a moderately loud level, at low levels it performs OK but when turned up a bit, the problem occurs. The amp in the other speaker performs normally at this level, and at a considerably higher volume without any problem. The speaker is certainly not being overdriven when the fault occurs, it happens at around 50% of its potential volume The question is does anyone know of a reliable repairer of this type of speaker amp module, or is there anyone on the forum who can diagnose / repair this amp or point me in the right direction?

[musicology]

Have you checked the fan and vent?

[Pe7e]

No, but it produces the fault in seconds even from stone cold (after standing in a cold room) it doesn't need to be warm at all. Someone has suggested it could be a faulty driver so I'm going to swap the amps over with the other speaker and see if the fault follows the amp or remains with the speaker, but I don't hold much hope of that being the case.