I want to Connect Roku to an old Panasonic TV with no HDMI port. The TV is 20 yrs old but works fine with my Comcast cable box. I want to stop renting the box. I bought the recommended Gana AV2HDMI converter to convert the Roku HDMI output to RCA inputs to my Panasonic. I get no picture on the Panasonic. Everything is powered up. Any suggestions?.
AV2HDMI sounds like the opposite what what you are trying to do. You want HDMI to AV (composite.)
Most of these adapters are NOT bidirectional.
Is this the converter you have?
Note that it has RCA inputs and HDMI output. As @Strega2 indicated you need one that works in the opposite direction, with an HDMI input you would connect to your Roku, and RCA outputs you would connect to the TV.
Here is one such device from Amazon: https://www.amazon.com/yoxxzus-HDMI-Converter-Adapter-Cable/dp/B0BVT8NRY6/
I don't know anything about this particular unit but it illustrates the sort of device you're looking for.
Read the reviews carefully and make sure whatver you get takes HDMI input and produces RCA (it may say AV or Composite, Component is not okay) output.
Be sure to buy from somewhere that has an easy return policy, because many HDMI-to-RCA devices do not do a good job of down converting output from a wide screen HD image device like a Roku to the narrow screen SD signal needed for an old standard definition display.
And finally, do NOT get an HDMI-to-RCA cable instead of a converter. It would do no signal conversion at all and would not send anything usable to your TV.