I think this is intentinal sanding of the chip markings done by the manufacturer to conceal the hardware for whatever reason. My TBC-3000 also has video A/D, D/A and (what I assume is) FPGA chips markings sanded. Though on yours it seems to have been done a bit more lightly.
The Conexant chips in the zoomed picture is a
BT-BT865.PDF video encoder which converts the digital signal back to analog. The sanded on from the other board looks like it has a Bt (Brooktree) logo. The company was
bought out by what later became conexant, so it makes sense that the chips may have changed from brooktree to conexant at some point.
I don't have a picture of mine here right now, but it looks similar to
this one.
I'm still curious to what other chips (A/D converter and FPGA?) datavideo used in their TBCs. The pictures I've seen have all been to low-res to make out what they are and on mine they are sanded as mentioned.
I've thought about adding heatsinks myself. I've found that the TBC very occasionally can output a messed up frame (there is a forum post somewhere from someone else with that issue but I can't find it.) so I've wondered if it could be overheating related.
Overheating does seem to be an issue on the Black AVT-8710 TBC we got, I think it's the FPGA chip in that case, but not really using that as it's one of the newer borked ones anyhow.