As mentioned by @jayeff, the TPS54334 regulator was the problem, however I don’t have the equipment to resolder since it turns out this chip also has a soldered thermal pad under the chip. I did happen to have an LM2596 DC-DC buck module (about $1.50 from amazon). I connected it to the 18v supply (soldered to pins 2 & 3 of CN8102 connector) and ground (thermal pads that were under the chip) and set the regulator output to 3.3v. Then I connected the output to the two large tabs (assuming test points) just above the chip (make sure to get polarity correct). No SMD soldering required. I used some heat glue to stabilize the board since there will be a lot of vibration from the woofer. Here is picture of the results - notice the blue module with LED where the chip used to be: