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(Don't know if I should make a new question, but it's partly related to my previous question).

I bought an old second hand oscilloscope (see Is my oscilloscope working or not?), a Philips PM 3253.

After some initial problems (and help of Electrical Engineering) I got it to work, however, except for the first half an hour, now every 10 minutes the mains group of the house goes 'down'... I don't know the exact English term... It means I have to go to the 'fuse box' close of the house to turn on the group switch back on.

Is there some easy solution for this or things to check on the oscilloscope, or is it some setting causing it?

(My electrical knowledge is not high)

At the end of the day I could have the power on for half an hour on without having the computer (on the same group on). Today I used a separate power mains outlet for the oscilloscope; maybe I put too many devices on an extension box. I will leave both on for an hour to see if it helps.

Update: I did some more testing and the solution was putting the power of the oscilloscope directly to a wall outlet (and not running through extension outlets).

Also I have added a cable to ground from a wall outlet to the oscilloscope GND input on the back.

I still have some problems with the oscilloscope but I will spend another post to it after I did some more tries to fix it myself. Thanks for your help!

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    \$\begingroup\$ Are you connecting the negative lead of your scope probe to anything that is at a nonzero voltage referenced to ground? \$\endgroup\$
    – Hearth
    Apr 26, 2017 at 22:15
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    \$\begingroup\$ Identify other devices on the same "group" that are operating at the time you operate the oscilloscope. It is likely that (1) your oscilloscope is the "straw that broke the camel's back" or else (2) you have a problem with or without the oscilloscope and all the oscilloscope does is to increase the frequency. Those assume you are using the oscilloscope correctly. If, however, you are also trying to apply it to circuitry and causing a short to ground, somehow... then that's another thing. It means you need to NOT DO THAT for now and learn more about using a scope on a plugged in circuit. \$\endgroup\$
    – jonk
    Apr 26, 2017 at 22:16
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    \$\begingroup\$ There ought to be a fuse in that scope stopping such things from happening. I'd recommend looking to see if that's been bypassed, first, then figure out what's wrong--a lack of fusing is a pretty serious safety problem. Though it won't solve your problem directly. \$\endgroup\$
    – Hearth
    Apr 26, 2017 at 22:34
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    \$\begingroup\$ Sorry, I'm not making it clear. There should be a small fuse inside the oscilloscope. Equipment like that is supposed to be fused. \$\endgroup\$
    – Hearth
    Apr 26, 2017 at 23:13
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    \$\begingroup\$ Is it the breaker (stop/zekering) that is tripping, or the RCD/GFCI (aardlekschakelaar)? These are two different safety devices, and they are triggered by different causes. \$\endgroup\$
    – marcelm
    Apr 27, 2017 at 11:43

1 Answer 1

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Older equipment like this frequently has bypass capacitors connected between the wires of the power input, supposedly for noise reduction. There will frequently be one between Line and Ground and another between Neutral and Ground. These capacitors leak enough current to trip a modern GFCI — something that wasn't a concern back when the equipment was designed.

The fix is to open up the scope, find the capacitors, and disconnect them. If you're not comfortable doing this yourself, find a friend who has the necessary knowledge. One source of such a friend (if you don't already have one) would be a local "maker space" or "hacker space".

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  • \$\begingroup\$ Thank you very much ... after putting it directly to a wall outlet the problem seems to be gone (at least while not changing the probe to something else, not tried that yet). But if I will have more problems, I will let a friend do it (I have some, but not nearby). \$\endgroup\$
    – Michel Keijzers
    Apr 27, 2017 at 11:59

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