Can I use a vivitar 285hv on my canon 10D using the pc connection without frying my camera?

SOURCE: Will a Vivitar 285HV fry my Canon EOS 40D?

Personally, I would not try it. While the Canon has a protection system built into the camera, the trigger voltage on the Vivitar is pretty high. I have had good results using a 283 on a slave shoe, you will have to stop down more with the extra light

SOURCE: No power for my 'old' Vivitar 285HV Flash

I've got three 285HVs and have had this problem. Obviously, make sure the batteries are good and the door and inside terminals are not corroded. The whine sound that you usually hear is the high voltage circuit. the reason it changes pitch is that the main capacitor is charging. As the charge gets greater and greater, the pitch with go up as the circuit changes the power being fed to the capacitor. If you don't hear the "whine" then it's either the HV circuit isn't working (probably not) or the capacitor has gone bad. These things are sealed but can decay internally due to their structure. Usually this is due to the dielectric components breaking down or the electrolytic goo drying up (usually what causes it).

Sometimes, you can let it sit with good batteries and the switch on to see if it will eventually start to charge the cap. Most of the time tho, this is an indication that the capacitor or the charging circuit is dead. It can be repaired but sending it off will usually be more expensive than replacing the unit.

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