Re: MSO 3012 input resistors / schematic attenuator board

Gary Appel

Just a thought...

It doesn't have to be a huge voltage, if it's at a high frequency. That 300 V RMS probably applies only to low frequency signals. The maximum allowable voltage is usually derated with frequency. I have damaged a probe by looking at moderate level signal levels (well within the low frequency rating of the probe) at 30 MHz.

Gary Appel

-----Original Message-----
From: arnoldniemeier via Groups.Io
Sent: Friday, November 30, 2018 7:32 AM
Subject: Re: [TekScopes] MSO 3012 input resistors / schematic attenuator board

It is unlikely you will ever know what they did... unless you pull the
attenuator out, remove its covers, and look for yourself.
Pretty easy work with any stereo dissection microscope.
That is what I've done and how I found the defective parts and fixed it.
The link to the Tek forum with pictures was in my opening post.

There is no further damage visible...
But damaged components are not always visibly damaged.
And that was the reason why I asked for the schematic.

To blow that resistor, your friend must have over voltaged
that input quite a lot. It probably involved the power line.
Yes is seems that it had a huge voltage because the scope is
specified for 300VRMS on the input.

But it seems there are no schematics available to do a good analysis on this circuit.

I will put it back together and use it again. Quite a shame that
documentation is not available any more these days...

Thanks anyway...

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