Those readings are all good. Where is the 7th tab on the transformer?
The schematic shows that it is the one with the thermal fuse. You need to measure resistance from the 7th tab to any of the other 6 on the primary.
The funny thing none of us have mentioned, this transformer can be wired up for any voltage, so it could have been rewired and you would not have needed the external transformer.
Edit: I think the 7th tab is where the white is connected up on the secondary side (with the orange and black wires).
The schematic shows that it is the one with the thermal fuse. You need to measure resistance from the 7th tab to any of the other 6 on the primary.
The funny thing none of us have mentioned, this transformer can be wired up for any voltage, so it could have been rewired and you would not have needed the external transformer.
Edit: I think the 7th tab is where the white is connected up on the secondary side (with the orange and black wires).