Looking for some HP LJ3 repair hints and a paper tray

Hi, I've got a Laserjet III that's intermittently throwing Service 50 errors. Fusing lamp tests good as per <http://www.fixyourownprinter.com/reference/guides/fuser/sx>. I assume this means the AC power module has fried itself. Best I can find on Google is that I need to replace the triac and some 'support components'. I can find component designator IDs, but not component values - does anyone know what needs replacing, and what to replace it with? It's also been throwing 13 Paper Jam errors, but there's no paper jam visible. Anyone know what causes this? I'm guessing the optosensor on the fuser assembly has failed, but I can't identify the opto. Does anyone have a part number for it? Finally, if by some twist of fate I manage to get this thing running, I'm going to need an A4 paper tray. Anyone in the UK got a spare they feel like parting with? Thanks. -- Phil. | Kitsune: Acorn RiscPC SA202 64M+6G ViewFinder philpem at dsl.pipex.com | Cheetah: Athlon64 3200+ A8VDeluxeV2 512M+100G http://www.philpem.me.uk/ | Tiger: Toshiba SatPro4600 Celeron700 256M+40G