unreg problems are always situated around that comparator circuit. in your case the opto. only two conditions around these comparators are valid. any other logic combination give 'unreg' as the cpu can't make heads or tails of what is going on. if the supply behaves correctly but still shows unreg then the circuit is at fault. on the other hand if the regulator goes wonky then unreg is normal.
275 is a steal for this beast. they are tanks , have excellent regulation and are very reliable lab supplies. i got a 3632a on the operating table that has a defect in the regulator. haven't found it yet ... gonna start swapping chips blindly soon ... ( semi blindly .. i have an idea what it is but i ordered the 4 chips , i suspect one of em is bad but for 5$ i'm not going to spend 3 hours finding which one , just swap em all...