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I have a weird problem on both channels of my MSO 3012. It seems to have only a
very weak capacity between the input and the measuring circuit. It does only display the
AC part of the probe calibration. And as you can see it is a very low level signal as well...
(Unfortunately it is not a broken probe wire. That could give about the same behaviour.)
Also external signal sources show the same problem. And on an external DC signal the line doesn't move.
Both channels have the same problem. So it might be a common problem. I've updated the
firmware to 2.31 hoping it would reset settings. But it didn't solve the problem.
Is there any documentation or schematic available for these scopes? And/or does anyone
recognise this problem and knows a solution? It looks to me like a fault in the attenuator Board.
Thanks in advance!
Here is a photo of channel 1, DC coupling, 20mV/div 1:1 on the cal output.
I've removed the metal shields from the input circuits.
Immediately I spotted two fried resistors. To test I've put two 47R resistors in parallel with the broken ones. The result was a normal measurement again...
It seems to me that the resistors are a part of an over voltage protection circuit...
But I'm not sure about the exact values of R0501 and R0201.
I hope anyone here can help me to get the schematic of at least the attenuator board.
Thanks in advance!
(At my work was a 4 channel version, and I've checked it there) I've replaced the
resistors with thin film 50.0 Ohm resistors. All ranges are working normal.
But I have some questions left...
What happened here? I think it had a huge over voltage/HF power. Probably
some crowbar construction with the 50 Ohm resistors protected the scope?
If there is a protection circuit, I would like to know if that is still working well.
Are there any schematics available on these MSO 3012 scopes?
No reply on my email to Tek...
No reply on the forum...
The schematic of the input circuit seems to be like this in a simplified way....
So if there is any info about that clamp circuit... Please speak up
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