Test the output on the Power supply no - load - does it rise to 13.8V and stay - then when you connect back to the radio the load drops?
Then disconnect the radio and take a 194 light bulb and just load the bulb to light it at the power supply output - and measure voltage - if it drops - that lamp is about 1/2 the demand the radio needs to work - so if it does drop to that 11V figure - the power supply is the fault...the float voltage and load voltage to handle a simple load - forcing it to drop - is from the AC ripple side it may have a blown or shorted diode in the bridge.
The thing has a separate power connector - so you can patch in a separate 5~7Amp power supply to take care of things while you repair the main one.
The "drop" may have taken out two (or three) parts.
One? Main Bridge Rectifier.
Which will start to produce AC ripple more than C304 (35V and 3300uF) can handle - the Peak to peak of the AC waveform ripple produced by the bridge will exceed the ratings of the cap and it will fail soon enough.
You didn't complain about a "hum" which means the Regulation side is still working - but the "drop" is from the AC component in the DC supplied to the Regulator - so it just "offsets" the drop by lowering the voltage out to a point that the ripple was contained by the Zener tracking the ripple (120Hz down to about 60Hz most Zeners can have a good recovery from) because the board it sits on is floating at the Transformers output level in the winds and the bridge just provides the DC "gap" and the caps filter the ripples in the "gap" and the Regulator then takes care of the hum and provides the "boost" needed as demands are placed on the power supply.
... else the radio is asking to be recapped...
WHY? Because the main regulation requires 12 to 13.8V to obtain 8V constant
Locate D60 - by the MB3756 "flat pack" regulator - it can start crowbarring (acting like it's leaky) forcing the power supply to fail faster because of the Zener working against the ripple present (if any) Anything it senses above 18~20VDC it will fire and pull down the power supply.
Next time this happens? To prevent further damages, install a 4A fuse in-line from the power supply Positive rail to the main PCB to protect the radio from excessive ripple which can destroy the radio faster than overvolting it.
