Oscilloscope blows fuses!

hi!

firts of all, as it is my firts post, thanks in advance for the help. and sorry for de english.

I have a GwINSTAKE GDS-1062A digital oscilloscope in the office. The other day, the oscilloscope was on but with both probes disconnected, when a coworker set up a tea in the microwave. In the same moment that the microwave ended its cycle, the 250V@1A fuse of the oscilloscope blew.
I supposed that it was due to a transitory high current/voltage in the power line; so I changed it for another and when I turned it on, it blew again.

I am about to disarm it and check the power source, but first I wanted to ask you if you have any tips of were to find. Maybe there is a cap that tends to fail and shortcircuit something.

of course I have searched and couldn't find a schematic.

thanks for the help!

I doubt that the microwave had anything to do with your oscope dying. Probably a bad capacitor or transistor in the scope's power supply is causing the problem. That's just a guess, but it would be where I would start.

Once you have witnessed the same problem occurring twice at the same circumstances, and, assuming that such events were actually connected, the first concern that would come to mind is a possible radiation leak from the microwave oven, but how does it could be induced to the instrument... perhaps Earth's grounding not correctly done which became unable to drain EMI artifacts ? Just a guess.

andre_teprom said:

Once you have witnessed the same problem occurring twice at the same circumstances, and, assuming that such events were actually connected, the first concern that would come to mind is a possible radiation leak from the microwave oven, but how does it could be induced to the instrument... perhaps Earth's grounding not correctly done which became unable to drain EMI artifacts ? Just a guess.

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yes! this is absoluttly posible. this is an old building and we have already had ground problems; in fact a new spear (javalin? I dont know hot it is said in english) has been installed.

xxopiumxx said:

... in fact a new spear (javalin? I dont know hot it is said in english) has been installed.

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Do you mean a new GROUNDING ROD has been installed? It does look like a spear (or javalin) in that it is about 2 meters long, is copper and has a point that is driven into the ground.

As for the fuse, are you talking about the fuse in the oscilloscope itself, or a fuse that protects the wiring of your building? I thought that you were talking about a fuse inside the oscilloscope, since it is equipment size (1A). I don't see any way that you could blow the equipment fuse with external devices on the line circuit, unless there are serious problems with the building wiring.

SLK001 said:

Do you mean a new GROUNDING ROD has been installed? It does look like a spear (or javalin) in that it is about 2 meters long, is copper and has a point that is driven into the ground.

As for the fuse, are you talking about the fuse in the oscilloscope itself, or a fuse that protects the wiring of your building? I thought that you were talking about a fuse inside the oscilloscope, since it is equipment size (1A). I don't see any way that you could blow the equipment fuse with external devices on the line circuit, unless there are serious problems with the building wiring.

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yes, grounding rod, I didnt knew the word. and yes, the osc fuse. the one that is close to the ac plug. there is another in the inner power supply but that one is fine. maybe some varistor broked ? tonight ill check and upload some images.

Is your building from a time before microwave ovens were invented? Its circuits might have a sensitivity which brings on problems as you add a microwave.

Hello xxopiumxx,
From the way you've indicated that the fuse has blown twice, then there's a strong chance you have a major short in the
primary side of the PSU.
Are the fuses that have blown glass types? If so, has the glass been blackened, thus having blown violently?
Here are just a few tips:
(1) Once you've removed the power supply from the scope, visually check it for any damaged, overheated and/or
discolored components.
(2) If you see nothing obvious visually, then use a multi-meter set to low ohms and measure across the main filter capacitor/s.
There will be either one, marked 400WV or two, marked 200WV on each.
If you find no shorts across the caps, then you need to look further along.
(3) Check the switching MOSFET or transistor for shorts as well.
(4) Check if there's a short between drain and source, (or collector and emitter) and the heat-sink that it's attached to.
(5) Check every diode in the primary of the power supply for shorts. The switching transformer should give you an indication
of which side you need to look. It will be the same side as the AC input.
(6) Any surface-mount semiconductors should also be checked for shorts.
Please let us know how you go.
Regards,
Relayer