Onkyo tuner repair

[Electrolitty]

Hello everybody,
I am working on a 1980s Onkyo T-4015 tuner. The voltage regulator 78M12 has failed, probably because the voltage shown in the red rectangle on the diagram is not 18V as marked but nearly 29V.  The mains transformer output AC2 to E is 21.5V AC. Unfortunately there is no indication in the service manual which voltages the transformer should deliver.
What would be the least invasive way to get the input voltage for the regulator down to a reasonable level?

[Fryguy]

The voltage at the input of the 78m12 ist unregulated and will go up if there is no load behind the 78m12 - 18V is with load and @ 220V mains !

Does the tuner work if you feed it 12 volts from a external psu ?

[Electrolitty]

The voltage at the input of the 78m12 ist unregulated and will go up if there is no load behind the 78m12 - 18V is with load and @ 220V mains !

Right, but the 7812 cannot draw a lot of power, otherwise the 10 Ohm/1 Watt resistor will burn (-> schematics).
By simulating a load of about 4W with a big resistor directly after the bridge rectifier, the voltage drops by 4.5V to 24V, much more as it would under load by the 7812.
Therefore I want to lower the voltage at the 7812 input by some means.

Does the tuner work if you feed it 12 volts from a external psu ?

The 7812 is not entirely dead. When I lower the mains input voltage (by variac) so that the voltage at the input of the 7812 is around 13V, the output then switches on again (at around 10.5V to 11V) and the tuner works. A bit odd I guess but that's what happens.

[Fryguy]

A standard fixed voltage regulator like a 78xxx needs a input voltage at least 3 volts above the output voltage to work properly .
If the one from your tuner starts doing something at 13v input . . . something ist terribly wrong with it !
The operating input range of this regulator is 15-30 V - throw this one out and put in a new one .