I know that it is a very old topic, but I didn't want to make a new one.
I have one question: HighVoltage did you manage to get this manual, and if yes could you be so kind and share it with us?
Sorry to say, but after a lot of effort and even some money out the door, I was not able to obtain a Service Manual copy for the PM6306
However, I was able to get a Service Manual for the PM6304 and that one is very similar to the PM6306. The only difference is really the front panel interface.
Send me a PM with your email address, so I can forward you the Service Manual for the PM6304
These are amazing meters and I have bought a few more of them, repaired and restored them and they look like new now.
I have even painted one completely new.
Compare my first picture above.
One of them even has all option, including RS232, DC, GPIB