CRT boards smell bad after cleaning off flux, anyone know why?

[CRTguy]

I recently re-flowed all the solder joints on my 1992 Hitachi CT2043B 20" CRT TV and used a lot of liquid flux to do the job. The solder I used was Chip Quick 63/37 Tin/Lead no-clean solder that I purchased in 2023. The flux I used was Kester 186 Rosin Soldering Flux that I purchased in 2019. Before I did any solder work on the boards, there was never an issue with them smelling during operation. When I re-flowed all the joints, I didn't clean the flux off for a year and during that year, there was a slight flux smell during TV operation but it was barely noticeable.

A few weeks ago, I used several methods to clean the flux of my Hitachi TV boards. First, I cleaned the flux off the bottom and top of the boards with a toothbrush and 91% isopropyl alcohol. I had to also clean the top of the PCBs because some flux still seeped to the top side during soldering and when cleaning the bottom of the board. However, when I did this, my boards had a really strong smell that sort of smelled like the flux I used and gave me a bad headache. I then cleaned the boards a second time using the same toothbrush and alcohol method and it cut the smell in half and the smell no longer gave me a headache. Then I let the boards dry and started using the TV again. After about 30 minutes of TV operation, that same flux like smell filled my small room and it was strong. I had to turn off the TV because of this.

Next step, I obtained some MG Chemicals 4140A flux remover and cleaned my boards using that and a toothbrush and it did nothing to remove the smell during TV operation. I went over the top side of the boards one more time with q-tips and alcohol and was able to clean off a small amount of residual flux that remained but once again, this did nothing to remove the smell of the boards during operation. It sucks because I really like my 20" Hitachi TV and it works perfectly but the smell from the boards during operation becomes so strong that I don't enjoy using the TV when this happens. I even cleaned the boards in my sink twice with soapy water and a toothbrush and rinsed them off well under the faucet and it didn't help. My next step might but to purchase the flux remover called "Flux Off" and see if that does anything.

I think one possible explanation is that some flux got trapped under some components or even inside some components. If that was the case, would there be any way to remove the trapped flux? Is there anything else that could be going on to cause the boards to smell after cleaning? Is it possible that I removed some sort of protective layer off the top of the PCBs and they are now off-gassing? Any input is appreciated.