Hello,
I don't know how to test the ua726, other than just popping a new one
in there and seeing what happens. Unfortunately, it's a rather
unusual transistor pair, and normal transistor testing procedures
don't really apply to it. It is quite possible that you have a bad
one, but you should also check out all the components that are in
front of the 726 first -- things such as opamps, passive components,
etc.
If you need another ua726, I have new ones for sale. They are new
old stock parts from the EML factory in New England.
Best regards,
Michael Bacich
Las Vegas, NV
702-454-0801