Cause of Failure. Undetermined. Possibly failed bridge rectifier,
BR40 (located center top), due to heat from the rectifier tube; or failed
filter capacitors C40/C41.Counterpoint used these capacitors in many
products and they have proven reliable in the long run, so overheated
BR40 seems the most likely cause.
Repair Options. At this time, we have no idea how to repair
this damage. The circuit board is too damaged to repair and we have
no replacement boards (the cost to make a new batch is a couple thousand
dollars and I will undertake it if this problem becomes common).
Suggested Course of Action: Before the damage occurs, remove
the suspected old parts and install new ones. This should give many
more years of operation. I would recommend replacing BR40 with a new
GBPC606 6A/600V (www.digikey.com, P/N KBPC606-ND), and the capacitors
should be replaced with new 6800uF/35V ones, no larger than 22mm diameter, and 10mm lead spacing. A part equivalent to the old part is the Xicon XRL35V6800 (www.mouser.com
P/N 140-XRL35V6800-RC, rated at 85 degrees C). A 105 degree C part would probably last longer, but I don't offhand know of one. You might also consider the Nichicon FX 4700uF/35V 18mm, 85C sold by Michael Percy Audio. It may sound better than the Xicon one.
We can do this work here at Alta Vista Audio for $435 for a pair
of NPMs (return shipping extra), but a skilled technician should be
able to do the work for less.