Right, where to start...

Your problem....

The first thing you need to establish is.. is it the CB that's at fault or is it something else.. If a radio is DEAD the first thing you need to check is the power lead
and PSU (Power supply Unit) Is it in fact plugged into the back of the radio or is it loose. Once thats established check the fuse that's in-line on the power lead.
Looking at it visually is normally ok, if the thin strip of wire between the two ends looks ok it normally is. If you have a continuity checker or buzzer just check to
make sure it is connected through and not blown. Then there's the good old PSU.

The PSU..
Most of these have a small illuminated light to let you know they are on.... or the hum from them is another clue to see if they have power going to them.
The main thing to realise is the fact that the illuminated light is on it doesn't mean that the power supply is actually kicking out power... or that it is actually 12v (or
13.8v). When the regulators blow on these normally it means no power or 24v out which wont do your CB any good at all. Thats easily spotted by the signal
lamp on your meter suddenly going brighter then in a lot of cases popping... likewise often the capacitors which are often rated about 16v in CB's.
A good idea is to use something like a 12v car bulb across the terminals of the PSU... if it lights ok then it probably is ok, if it goes really really bright the PSU
may be kicking out 24v (stop using it immediately)

The Mic...
This is also a common fault. If the wiring in the plug comes loose or breaks off the radio will be affected in a number of ways..
One is there may be no outgoing modulation... people will see your signal but wont hear your voice... or.. there's meter movement on your CB but theres no
sound.. or a tiny noise if the radio volumes turned right up (make sure your squelch is open first though) .. or.. the transmit keeps cutting in or out or the radio
doesn't transmit at all...
All these faults can be caused by a faulty mic plug or mic cable and it is a good idea to always have a spare to check or borrow someones with the same type of
radio (just because its a 4 pin plug though  doesn't mean the radio's are wired the same so watch out for this)

If you can't borrow one to check then make sure you bring the mic along to the rig doctor so that he can check it as well otherwise he may just check your radio
with his spare mic and find no fault... and charge you for it too..

Most rig doctors (including me) prefer to just have the radio so don't bring the mic (unless you think its faulty), power lead or thumbscrews/brackets because we
are busy creatures and sometimes forget to give them back with a radio.. no we're not thieves... it just happens... On my repair dockets I used to write exactly
what the customer supplied so there was no argument later on.

Rig Doctors Skill..

Now you must remember here that word of mouth is a very important thing for CB repairs... ask about local to you if anyone has used a rig doctor and if they
were satisfied with their work. There is NO CB REPAIR COURSE so most rig doctors use their skill and judgement to determine what fault your CB has... and
how to repair it through experience. Most of the rig doctors skills have come from practice, studying others work and experimenting...
Some lesser people will just cut out a protection diode.. not replace it then charge... that's all well and good but if the CB is ever cross connected in the future
there's no protection diode to kick back the voltage to blow the fuse.. it goes straight into your radio and.. pop... hefty repair bill...so asking around is always a
good idea.  Also if a rig doctor can't find a fault and can't do the repair it doesn't mean another wont... it doesn't mean the first is useless... it's just that the
second has come across the fault before so has a slightly better idea of the fault.

NOW another important thing to realise is a rig doctor is all you have...  and rig doctors don't know everything about every radio. They only know what they have
done in the past and what others may have told them. There is no qualification for CB repairs and rig doctors aren't rocket scientists... If they were they would be
earning a fortune doing a highly qualified job.. not spending up to an hour or more fiddling with your rig to earn peanuts which is what most people who have
their CB's repaired expect to pay.

Finally it's important to realise that Rig Doctors have lives so can't always work to your time-scales. Give them some leeway...
CB Radio Repairers in the UK
CB Radio History from its early days