I was using my CT800 at a flea market building with a marginal electrical system. Unbeknowinst to me, the outlets were not grounded. When I placed a mixing board on top of the CT800, the cases grounded together and sparked. After that, I refused to operate my equipment in the building. Only problem was the damage had already been done.
The CT800 stopped working in the right hand channel. A short had developed between B+ and ground, leading me to believe it is in Q309,310, or 311. I was looking over the schematic of the amp however, and I cannot seem to figure out for the life of me how the chassis ground works.
The speakers are grounded back to chassis ground, and the chassis is at earth ground potiental through the 3rd prong of the power outlet (which was not hooked up in the venue I attempt to use it at!). In a typical power supply, the negative side of the bridge is tied to chassis ground, and the positive side is tied to the components. Of course, in a n AB+B amp such as this, it's different. The negative side is tied to components as well, with the ground appearing to "float" between the B+ and B- supply voltages.
Now what has my head scratching is how this actually works. I do not see any ground reference point off the power supply to tie it all together. I would think there would be a center tap on the transformer or something of that nature, but there isn't. From what I can tell, even if I was able to use my CT 800 at this venue without damaging it, I would not get any sound, because the earth ground was missing. Am I correct on this thinking? Also, wouldn't these amplifiers trip GFI outlets when the current from the speakers is detected on the ground terminal?