Fixing a broken Metcal handpiece
I've got a similar Metcal system. If the handpiece and cartridge are working properly just the green LED on the STSS power unit should be on, otherwise the amber one will be lit as well.

They use RF heating at about 14 MHz, via a coaxial cable. It's very unlikely that you will get that handpiece working properly, I'd just buy a new one. You could try testing the power unit with a suitable 100W 50R resistor, it'll need to be non-inductive. Just the green LED should come on. I can't be sure that test will work as I don't think the impedance has been published, but it won't do any damage.

I got mine second-hand from a supplier here in the UK, with a new MX-500 handpiece and selection of cartridges. I subsequently picked up a second STSS unit on Ebay, as a spare. The power units are very reliable, so yours is probably OK.