Hi @bob_griffiths ,
Here’s a [https://www.vintage-radio.net/forum/showthread.php?t=156289|link] that may be of some help.
Having a DMM (digital multimeter) and knowing how to use it will be a definite advantage. As stated in the link there is no information out there for the radio e.g. schematics, service manuals, parts lists etc to help so you may have to start from scratch.
Changing the power supply for a known good power supply has eliminated it as the problem so the next step would be to prove that the switch is working electrically.
If it is OK then after that it becomes a matter of tracing the power rails through the radio. Not easy without the schematics though.