Hi Darren,
I presume from your statement of "fm fitted" you actually mean the radio has been modified or 'wide-banded' to transmit on CB frequencies. (FM is a modulation mode as in 'Frequency Modulation' which this radio is equipped with as standard.) Just clearing this up for others that may also be reading this posting.
You also state in your posting title that the radio is not receiving but in your posting say "i do not get a good signal". Is it totally 'deaf' as in receiving nothing at all or does it actually receive but less than expected? Again this is an attempt to clarify the problems you are facing so that people may try to help you.
If the FT990 is actually receiving and you are comparing it to the CRT SS6900 are you receiving the same signals at all or is it more a case of s-meter readings or audio volume levels are different?
It may be worth a peruse of the FT990 user manual and make sure you have any settings correct such as the 'ATT' switch etc.
An online version for download or browser PDF viewing can be found here :-
http://www.radiomanual.info/schemi/YAESU_HF/FT-990_user.pdf
Any further information you can provide will help others to help you.
Re: Alan Pilot
Alan, I can see where you're going as this radio does have the 'receive' antenna facility but there is only one SO239 on the rear. However it's worth Darren checking that this feature hasn't been inadvertently activated and hence the link to the user manual.
All the best,
Victor
Edit:- I've also moved this posting to the 'HF Radios' section of the forum being more appropriate for this type of query.(It was in the 'Nets & Skeds' section.)