the short answer is, it depends...
there are too many variables to give you any kind of answer besides, "send it to a good shop".
see, if the radios are old, thats one set of problems.
if they are both relatively new, thats another set.
also, you dont mention anything about how you tested the radios, how they are set up, what antenna you are using, etc...
the weak radio may just need an alignment, or it might have one or more blown parts inside.
one thing to check before you go any further, is if you had the RF gain turned down on one of the radios.
RF gain is the receiver's gain, and turning it down desensitizes the receiver.
99% of the time, this control is left at maximum. (clockwise)
if you are driving down the road and you notice a signal pegging the meter on your radio, you might want to turn the RF gain down a bit to avoid overloading your receiver.
so, first make sure the RF gain is all the way up on both radios, then give as many details as you can about your situation.
if the problem is inside the radio, most likely you wont have the skill or tools needed to fix it, so a shop is a good way to go.
there are quite a few owners of good cb shops right here on this forum.
good luck,
loosecannon
...runna pile-up on 6m SSB