NAD 3020 DC on right channel

Hi all. Could someone please help me?

I have an old Series 20, with the 4 caps in the middle, which has -7.5v on the right channel.

I've replaced the output and driver transistors to no avail, but have confirmed this works fine through headphones, and through another power amp.

The concerning thing is, C622 swells considerably, then blows, which I'm sure is related, but I'm not sure how to track down what's blowing it.

Any help is greatly appreciated!

-Dave