Thanks for all input, everyone! Now, the saga continues...

I've checked the transformer: one winding produces +19.2v, -19.2v and
(I assume) ground, the other produces 10v and ground.

Continuing to main board, there is a diode bridge and from there 3
regulators: 5v standby, and +15v / -15v controlled with a relay.

A relatively big resistor immediately before the input to 5v regulator
is cracked and the solder has evaporated from its connection. Also,
there is a leaked cap in the -15v circuit.

I can replace the resistor and the cap, however how can I check that
the regulators (7805C, 7815C, 7915C) are OK and the load is not
excessive, so as not to create any additional leaks and explosions?

BTW, I do have electronics knowledge (B.Sc in EE), however zero repair
experience... One has to start somewhere

Thanks,

MaxVT