I can give you some idea of possible issues but it's speculation, But it's base on 50 years of component level troubleshooting on this type of chassis. I usually say that it's not rocket science but it can seem that way. There is a transistor in the radio that is directly modulated by TA7222AP since you have receiver audio it's a given? that the Audio chip is good? anyway, the transistor I previously spoke of is generally fed directly by TA7222ap IC. It has been known to carry the numbers TR35 AND TR34 respectively if either one of these is bad it would or could cause no modulation on transmit. Problem is you are not seeing any SSB output as well so this circuit may or may not be an issue. First If I were training a new tech to troubleshoot this from the wiper of the mic gain control on through the path to C121 making sure you have audio along that path right up to R99 then checking TR32 for Collector > emitter short so forth and so-on etc. Oh I included a schematic of the Washington it may help. Ok well if you send it in you should know that the few that know what they are doing will suggest you replace all the electrolytic caps which most would here would also suggest do you have to do that YES/NO it is possible that the radio could function fine for some time but the caps are all 35 years old. This can run anywhere from 60 to 100 depending on where you send it and what quality of Caps they use another $25 or 30$ for shipping and then if the Caps don't fix the issue Well it would be more most likely. Well, I got it started if I made any mistakes, misspellings, goof-ups etc please, by all means, somebody speak-up.