Products > Test Equipment

New toy(?) scope Fnirsi DPOX180H, claimed 180MHz/500MSps (May 2023)

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BillyO:

--- Quote from: imarcinszn on September 07, 2023, 04:36:46 pm ---Has anyone tried to change it, or found where AC blocking capacitor is located?

--- End quote ---
You should be able to trace back from the BNC connector.  It is usually VERY close to the input.  BTW, adding a capacitor in series with another capacitor will reduce the total capacitance, not increase it.  If things improve it might be due to conductive contamination on the PCB or a faulty blocking capacitor.

EDIT:  BTW, there is clearly a relay in each of the front ends.  There may also be some CMOS bilateral switches.

ru_tash:

--- Quote from: BillyO on September 07, 2023, 05:34:16 pm ---
--- Quote from: imarcinszn on September 07, 2023, 04:36:46 pm ---Has anyone tried to change it, or found where AC blocking capacitor is located?

--- End quote ---
You should be able to trace back from the BNC connector.  It is usually VERY close to the input.  BTW, adding a capacitor in series with another capacitor will reduce the total capacitance, not increase it.  If things improve it might be due to conductive contamination on the PCB or a faulty blocking capacitor.

EDIT:  BTW, there is clearly a relay in each of the front ends.  There may also be some CMOS bilateral switches.

--- End quote ---

i think he used DC input with external capacitor added.

imarcinszn:

--- Quote from: BillyO on September 07, 2023, 05:34:16 pm --- BTW, adding a capacitor in series with another capacitor will reduce the total capacitance, not increase it.

--- End quote ---
Yes, that is right, but I've tried with DC coupling mode so the external capacitor should be the only one. So I guess that higher value  still should help with that issue. Connecting external 22nF capacitor produced similar to the internal capacitor.


--- Quote from: BillyO on September 07, 2023, 05:34:16 pm ---EDIT:  BTW, there is clearly a relay in each of the front ends.  There may also be some CMOS bilateral switches.

--- End quote ---
I wasn't specific enough. There is clearly one relay, but it is clicking when vertical scale is being changed. During DC -> AC coupling mode change there is no sound, so it needs to be changed by some kind of solid state circuitry.

I performed some measurements and i think that this is AC blocking capacitor:


At the input (just at the output of the relay) of this capacitor signal is the same, no matter if it is AC or DC coupling mode:


Output of this capacitor on DC mode:


And output of this capacitor on AC mode:

There is still some overshoot on DC mode but it is not visible on the FNIRSI scope, but at least it contains DC offset

svetlov:
rise time 1.8 nanoseconds  :bullshit:

Kon:
Подскажите какая микросхема отвечает за смещение для калибровки.Появилось остаточное напряжение на индикаторах.Что то вышло из строя.Штатная калибровка не помогает.Всё остальное работает.Или можно уже выкинуть осциллограф?Снимок без щупа.

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