[Amps] Hot Chasis Problem

[Will Matney]

To eliminate the transformer, take the transformers HV leads loose and measure one lead to meter, and meter to chassis ground using an ohm meter, leaving one transformer lead open. If you get a reading, you have a transformer that is shorted out (coil shorted to the core). If it shows an open, it could be breaking down with voltage applied. In this case, try taking loose both HV leads and apply the line voltage across the primary. It would be best to use a variac here to do this. After applying power, turn up the voltage slowly and watch for voltage to appear on the chassis. Here you would read any voltage from one HV lead to chassis ground with the other HV lead loose. That should show it breaking down under open circuit voltage. If nothing here, most likely you'll have something leaking like a rectifier or a capacitor. Also, look to see if there's maybe a shunt resistor opened up off the last rectifier in the stack to ground where the B- goes out. If the shunt was open, this would show a high voltage between it and ground.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 4/29/05 at 7:14 AM aborg wrote:

>This chassis definitely is hot, it bites pretty good.
>Using 
>a piece wire touching from chassis to another contact
>chassis point yields a pretty good spark.
>#########################################################
>
>--- Sam <w4oae at comcast.net> wrote:
>> Your hot chassis could just be a phantom voltage
>> reading.  IE there isn't any real current potential
>> between the B- and chassis ground.  Due to the very
>> high impedance of the probe it shows a voltage
>> potential due to the internal resistance of the
>> probe being so high.  Try shunting the HV probe with
>> a few megs of resistance and see what happens.  
>> 
>> W4OAE
>
>Mike-KK4MS
>a_borg at yahoo.com
>
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