On Thu, 4 Feb 2016 13:59:27 -0000 (UTC), Cursitor Doom
wrote:

Hi all,

I'm now working on a different Philips scope which 'died' suddenly for no
apparent reason. Here's a summary of the key points:

The smps section had power in, but nothing coming out.
I checked the smps outputs for shorts/low-res.
One output marked 45V was trying to feed a board with an input resistance
of only 6 ohms.
I located the board in question. There were several multi-pin connectors
around the edge of it running off to other parts of the scope. Now it
turns out the smps runs perfectly fine when *one* of these connectors is
pulled from the board.
With the suspect connector's plug disconnected, the aforementioned 6 ohms
shoots up to about 15k and life is great.
*BUT* (and here's the thing) the resistance looking into the suspect plug
(which has only two wires) is several megohms. And yet this very high
resistance, when plugged into the board causes such a voltage drop that
the smps shuts down! How is this even possible?
I keep thinking there must be something simple I've overlooked, but can't
think what it might be.
If anyone has experienced something similar in the past and remembers
what the underlying issue was, then that could be very helpful!
Thanks.

Regarding "How is this even possible?", I can think of two things. One
is mechanical - plugging that 2 wire connector in causes a short near
the socket. Can you unplug the other end of that cable and see if you
get the result? The more likely cause is a voltage on that two wire
cable turns on a transistor or some other device hard wihich then
shorts the incoming line from the power supply due to a bad part
somewhere else on the board. Good luck.