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DS1054z Square Output Problem

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m.m.m:
I lent my DS1054z scope to a friend and they apparently used the square wave output which is for probe compensation calibration, as an input for an opamp. I do not know what their circuit was, but after returning, the square wave output is limited to a 50mV voltage.
My guess is that they drew too much current and the output buffer of the square wave generator (if there's any) is blown up.  :-BROKE
I would appreciate your comments, or your experience if you had a similar accident.

modoran:
Just open the scope and see what's the problem there. And never lent to "friends" again.

TurboTom:
It seems there's one SOT32 device directly connected from the test signal output to ground, presumably a protection device (Z-Diode, transient suppressor) and then some RC stuff to the test signal generator "silicon" output. So the first item I would look at, especially if there's still "a little" of the signal present, is the protection device for a short. See here for a series of photos of the "later" PCB version.

I don't expect the test signal output can be damaged by shorting it to ground externally. But application of a reverse voltage would surely be able to cause some problem...  :o

m.m.m:

--- Quote from: TurboTom on December 09, 2023, 10:52:50 am ---It seems there's one SOT32 device directly connected from the test signal output to ground, presumably a protection device (Z-Diode, transient suppressor) and then some RC stuff to the test signal generator "silicon" output. So the first item I would look at, especially if there's still "a little" of the signal present, is the protection device for a short. See here for a series of photos of the "later" PCB version.

I don't expect the test signal output can be damaged by shorting it to ground externally. But application of a reverse voltage would surely be able to cause some problem...  :o

--- End quote ---
I just had the time to open the scope (I've been quite busy  :-[). My multimeter reads a ~30 Ohm resistance from the test signal output to the ground. So I think the protection diode is short.
The diode has the marking "1UW". It appears that the part number is PESD5V0U2BT. Please correct me if I'm wrong.
I'll try to order a replacement and report the results.
Without the diode, the resistance is ~25k so I hope the rest is good.

TomKatt:

--- Quote from: TurboTom on December 09, 2023, 10:52:50 am ---I don't expect the test signal output can be damaged by shorting it to ground externally. But application of a reverse voltage would surely be able to cause some problem...  :o

--- End quote ---
+1

Sounds like you are on the right track.

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