Re: 2465B leaky voltage

Chuck Harris
 

Let's gather some solid evidence:

The bond wire in the IEC style power cord goes
directly to the chassis by way of the mains power
line filter module.

It is a belt and suspenders system. The filter
module is in a metal can that has a metal mounting
flange that is screw mounted to the scope's chassis.

Inside of the can is a strap that goes from the bond
wire pin of the socket directly to a terminal on the
back of the can. The terminal is riveted to the
can.

The ground terminal on the back of the can has a green/
yellow wire soldered to it. The green/yellow wire has
a crimped on closed ring lug that is affixed with a nut
to a riveted threaded stud on the rear panel of the scope.

The rear panel of the scope is screwed to the chassis
using multiple screws.

The BNC connectors on the 2465 are directly (mechanically)
connected to the chassis at the front panel beneath the
bezel ring. Each has its own torx screw.

Assuming that the scope is the problem is a poor idea.
First do some measurements.

Connect a good low ohm meter to the offending BNC connector's
shield connection. Measure ohms to the front panel ground
banana socket. Measure ohms to the bond pin on the rear
IEC power connector.

If either of these measurements is not very near zero ohms,
you have a problem within your scope. Most likely inside of
the rear power filter... usually a burned out strap due to
a very, very high current path from the filter bond pin to
the filter hot mains lead... or possibly a manufacturing
defect.

By very near zero, I mean less than 1/4 ohm.

Next, unplug your power cord from the wall outlet, and
plug it into the IEC connector on the back of your scope.
Measure from the bond wire pin of the cord to the
front panel ground banana socket.

If it is not very near zero ohms, you have a bad power cord.

By very near zero, I mean less than 1/2 ohm.

If these grounds are correct, your problem is likely in your
bench power, or your house grounding system.

-Chuck Harris

M Yachad wrote:

Correct on the 230VAC assumption!

I've checked that it is "grounded" - there are Y capacitors in the sealed EMI-filter unit - right at the AC input, and I'm beginning to suspect those of failure.

All the caps are new, so those 2.2nF's are not suspect.

The 113VAC voltage exists, even if the machine is switched off.



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