sparks31

I am an electrician and have just started to help out at a local hall. They have a few betapack 1's and all seemed fine until recently we lost channels 5&6 on one of the sets. The fuses are ok, neither channel works on the test button, i swapped triacs with Ch 2&3 but still 5&6 only do not work. Any advice on what to try next would be great, as mentioned I am an electrician, but have only basic electronic knowledge