Yamaha Mx800 Popped And Protection Circuit Activated

I recently bought a vintage yamaha mx800 to replace my mx1000, when delivered it was damaged. the damage was mainly to the back panel, which I straightened out somewhat and since it still functioned, left it at that. it has been functioning as desired until a couple days ago when POP and smoke from from the right rear corner (looking from the front back) and protection circuit activated. I was at low volume, however the amp was at full power output, it just seemed like a capacitor blew, I have 4 cervin vega DX9's rated at 4 ohms ea with the amp on 2 ohm output, that where I learned a $1,000 lesson with the mx1000, that one just fried but this one was different. I have been teaching myself electronics repair and have had success as I will this time, so I'm just looking for tips or help with diagnostics, thanks