ARC Ref 150se bias question

Well, trouble in paradise. My brand new ARC Ref 150se which I bought as an unused store demo with 3 hours on the tubes (OK, almost brand new) does not check out bias-wise. The tubes are biased in sets of two. You adjust the lower numbered tube and a second tube is slaved to it. The "master tube" has a bias pot and the slaved tube does not. The master is set to 65mV and the slave is supposed to automatically be between 57 and 73. Well, three pair of my four check out just fine but on V5 (as labled inside chassis) when you set it for 65, the slaved V7 only reads 40 or so. The instruction manual is devoid of any advice as to what this means and what measures should be taken. Any advice short of taking it to a tech? As bought from third party for dealer, last thing I want to do is ship it back to the dealer.