That is not necessarily correct.
To be clear, it is not uncommon for there to be separate internal power supplies for the lamps and the other internal electronics. Just because the lamps come on does not mean that the tuner section or other sections of the tuner are receiving the correct voltages.
In terms of trouble shooting, checking for the correct power supply voltages not only means checking to see in the power supply is producing the correct voltages (working) but that those voltages are making it to the correct part of the tuner.
It may not be a switch issue, but just because it worked then did not work does not in and of its self rule out a switch issue.
While there are other possible causes for the issue, the only way you will know is to do some basic trouble shooting. Given the symptoms, starting with making sure the correct operating voltages are making it to the tuner section is a very good idea. This is basic trouble shooting 101.
If the correct voltages are in the correct places then you move on with the trouble shooting process.
Some additional information. Note the different connections, circled in red and blue for the lamps and the rest of the power supply. The lamps can work without the correct voltages for the rest of the tuner.
I took a quick look and did not see a schematic for the 4080, this is from the 4020, but is likely to be similar, at least with the dial lamp and operating power supplies being separate.
View attachment 1039040
Again, there may be other issues, but one needs verify correct power supply operation, including voltages making it to the correct place (possible bad connections, solder or otherwise), then move on the other possible causes.