According to the Sony Service Manual for the PFM-500A3WU, 12 22 means either the Plasma Panel has failed or the Power Supply has failed. 12 means "warning decrease of panel high voltage" and 22 means "warning of decrease of middle panel voltage". If you get a 99, that means it has found the panel defective. So, if you're just getting 12 22, I'm guessing that it just needs a new power supply, but in searching for one, I've found that they are $1400. Probably not worth it. I'm working on mine to see if there's a fuse out or something that can be fixed easily and cheaper.

same problem here, anyone can help ?