Hi, and welcome to the forum.
This kind of problem is a lot like telling a mechanic "my car won't start". He'll start with questions about what does appear to work. Do the dashboard lights come on when you turn the key to the first click? Do the lights dim a little when you turn the key farther? Do you hear a "click", or does it just go "ruh, ruh, ruh" and won't catch.
First thing I would want to know is how many people have tried to fix it since it first broke down? Clearly they did not succeed. For every attempt at repair that fails I have learned to expect at least one new fault added to the original one the prompted taking the covers off.
Troubleshooting is a methodical process of identifying which parts of the radio aren't broke. The mechanic will check to see that the motor is getting fuel and a proper spart pulse first. This radio is almost 45 years old. Don't assume that it has only one fault, even if nobody has had their hand in it since it failed. 45 years can be an awkward age for a radio. The mileage will have a lot to do with what's gone bad. Just one problem, there is no odometer to read the miles from.
A low-mileage radio usually has fewer faults.
Just what tools do you have? Like getting your car to start, you'll need the right tools. At a minimum, a dummy load, wattmeter, general-purpose multimeter and soldering/desoldering setup. A frequency counter to see what frequency is coming out of the radio when it transmits is nice, but only necessary if the radio has a problem with that.
IIRC, this radio's circuit board has foil traces on both top and bottom surfaces. There will be metal sleeves that join the foil pad on one side to the pad on the opposite side of each hole. This can lead to puzzling issues if that sleeve accidentally gets pulled out of a hole while removing a component.
It was a higher-tech CB when it was made, but that really was a long, long time ago.
I can't find service data online. I'll check to see if I have any at work when I get there tomorrow. Probably not, but it's worth a look.
73