The Schneids wrote in
:

Kirk S. wrote:
Hi,

I'm trying to figure out a dead monitor power supply that uses a
UC3842B controller. I'd like to hook my scope to the chip and
observe any signals during startup, etc. Since this is connected to
rectified line voltage on the ground plane and a large power resistor
on the vcc line, I'm unsure where to hook my ground for the scope
probe. I'm using an isolation transformer, variac and series light
bulb in addition to the scope.

I'm just a tinkerer used to scoping clock signals on TTL circuits and
hesitant to do something that will toast my scope.

Any suggestions? Oh yeah, no schematics for the monitor either. I'm
looking at a similar schematic using the same control chip. I see
the startup voltage of +16vdc and no reference voltage or output
strobe signals.

Help!

Kirk S.



I've worked on these a lot - I don't use the scope anymore.
When I did, I made sure the ground of the scope was floating -

The WRONG way.
You're supposed to isolate the DUT,not the test equipment.

use one of those 2 prong to 3 prong adapters to isolate the
ground.

Leaving the scope chassis potentially HOT,a clear hazard.




--
Jim Yanik
jyanik
at
kua.net