Hi PiX
NO. This is an “X2” capacitor which is mains rated, that is it can handle the mains power at 240VAC. Capacitance 1.0knF or 1µF @ 275VAC. The X2 is a type designator and signifies mains use.
See not quite enough information first time around.
That also tells me that the 500V caps are electrolytic and they probably were operated at 300V+
True that WOULD give you a nasty sting if you happen to find one charged up. The secondary effect like colliding with a sharp object when you get the “bite” would most likely cause some damage.
The 2 heavy inductors along with the X2 caps would be part of a mains filter. The light blue discs are probably varactors as part of the filter.
390µF @ 500V electrolytics would indicate a high voltage (300V +) DC power supply for this machine so make sure any mains lead is unplugged before fiddling…
It would be common practice to have some sort of bleed resistor across each of these caps so if it has been unpowered for some time it should be safe. Would not hurt to check for any residual voltage though just to settle your mind. You can do this quite OK with a DMM.
A 5V plug pack does this too but doesn’t produce 500V.
Cheers Bob
1 Like
They will almost certainly be smoothing capacitors following a full bridge rectifier, so they were run at ~350V (240x1.4). Usually they will have a discharge resistor across them - look for a high value high wattage resistor across the capacitor. Even if it’s not there the voltage will have dissipated if they haven’t been run in a while. Get a well-insulated screwdriver and just touch it across the terminals - there might be a bit of a crack and a small spark, but it’s nothing to be concerned about if you are well insulated through the screwdriver handle and you are expecting it.
@Jeff105671 ve heard of people doing this.
Maybe im game.
Im not sure how much rubber and plastic i need between me and 500v. Is this a well insulated screw driver?
Ah that’s comforting.
I’ll give it a go.
Would have never guessed that 
It’s not between you and 500V. It’s 500V between the terminals - nothing to do with you unless you touch a terminal. That screwdriver looks fine. To be super-cautious you could be sure you are not touching the frame while shorting the terminals, in case one terminal is at frame potential.
That screwdriver is much safer than multimeter probes. With the probes the current flows through the cable (across the back of your hand??, over the frame??) through the multimeter and back. With the screwdriver it flows across a centimeter of heavy steel. It is a good habit to get into to discharge any capacitors that are part of a power supply as a matter of course whenever you open a case, even a 5V wall wart because some of them do have capacitors across the supply and sometimes they don’t bother with discharge resistors because there isn’t the room.
1 Like
Hi Jeff
I wouldn’t say that although both are OK in this instance. I would suggest the modern day DMM probe would be equally as good as the screwdriver. The surface area of the insulating material between the business end and your fingers has a lot to do with the actual breakdown point.
Good advice. Reminds me of my working days.
One project was the installation and commissioning of 40kW HF transmitters. These had quite a power supply. The PA was valves in a grounded screen configuration. -1200V on the cathode with a further -300V supply sitting on that for grid bias (adjustable). The anodes had about +6500V volts and the whole thing would supply some 10.5A without upsetting any overloads. The filter caps were I think 16µF 10kV oil filled paper types. They had bleed resistors across them but still took some appreciable time to discharge. There were mechanical interlocks on the access doors arranged so that when any door was opened a great big shorting bar came down across the caps and discharged them in a big hurry.
You can imagine the size of the spark if you switched the unit off then opened the door too soon. BANG!!! Big time.
Cheers Bob
