Is there a way to troubleshoot or fix this antenna?
Google Antron 99 problems or Antron 99 internal solder joint or something along those lines.
I remember reading a thread on some board or forum where users were finding poor solder connections in the base of the antenna.
If my memory is half good, it was several users who found the same problem with Antron 99 antennas.
I remember the thread having pictures of the poor solder job in the base of those antennas. I don't recall if it was a poor solder joint at the inside of the SO239 jack or a poor joint where it fed a coil.
The thread was very likely here at RR as I don't frequent many other radio related boards. It could have been in one of the amateur forums here also as some use the 99 for 10 meter work.
Good luck!
I just searched for antron 99 internal solder joint problems and saw several hits and sites about this problem.
I also saw reference to a pdf that said it showed how to get the antenna apart to fix the solder joint without ruining the antenna but the link was a dead link. I did not try searching for the pdf by name but chances are that it can be found.
It did seem like you may trash the antenna trying to open one up for repair.
I had a 99 back in my CB days and it always worked well with no SWR issues but maybe quality control was lost in newer builds.