Yes, I can see 3 sets of diodes for AC rectification, and, as phase has said - there is also an extra terminal block that is not connected in your photo.
I would look up the standard pins for opamps, one or more will be ground, one will +Vdc and one will be -Vdc. Then you can check to see if you have DC voltage at the pins of the 2 opamps, middle top of your photo. I expect if you have DC there then they will probably work.
You could then try and parrallel your 12vac so that all terminal blocks have 12vac. I am unsure that this is safe and will not do damage to the board though so please maybe wait to see if another member thinks this is a good idea!
I expect that the worst that could happen is that the regulators get hot, but it may be ok to test,
Stu