Thank you for Herb Johnson who helped troubleshoot and advise repair strategy
I bought an H-19 terminal a while back for parts. The previous owner had started converting this computer into a sort of H-89, with power for disk drives and a cassette port. She/He did not get very far.
Voltage regulators on the display control board - OK
Power supply controller - bad 12-volt regulator (103). Not needed if we're just reverting to a H-19, but might as well fix if ever in the future someone wants to upgrade this to an H-89 with drives. UA78H12S0
Adjusted the yoke to align the display
Serial port is marked "330-337", near the brightness knob.
Now it works great, using now for testing systems.