It used to work. To help troubleshooting, I borrowed a friend's pi - same model, memory, etc. When I switch the pi using the same cables, power supply, and memory card - the hdmi works on my friend's pi but not on mine. So there is clearly a hardware problem on my pi.
I got out my magnifying glass and started examining the components, especially those around the hdmi connector, but nothing has jumped out at me yet.
Are there any components I should focus on to try to find out why hdmi output no longer works? I can log into the pi over the net and execute all commands - there's just no video signal going out the hdmi cable.