Fortunately all the ICs inside the cx80 are common off-the-shelf parts, so you won't have problems sourcing replacements for those.
But, as suggested by mr_me, first ensure to exclude the most obvious fault, that is the cable.
I'd also clean the JS-TB switch, as well as the connector pins with contact cleaner.
If you have an Harmony cart or UNOcart for the 2600, try the roms in the first post of this thread to test the controller in real TB mode.
- Jase likes this