Sniffer XR-71 help

[Carl-NC]

Your oscope is set to use 10X probes; are your probes also set to 10X, or are they set to 1X?

[pito]

Take another photo of this area on both sides of the PCB

[kt315]

green trace is the output of the LF365 at pin 6, and the yellow trace is the input of the LF357 at pin 2.
I still don’t understand what you mean by the ‘classical’ view.

Also, in my new board I’m using a 7812 to keep the voltage fixed at 12 V.”

MAIN RULE is - if you measure the analog signal ie opamp output, you have to set GND-GROUND probe of your o-scope on D6A pin 1 - Voltage Divider (your schematic).

Classic is TYPICAL FORM OF THE SIGNAL. your signal is ununderstanding for me.

[pito]

Should be enough, DC voltages on diodes ?

[Jafar]

“Is the capacitor shown in the picture not sufficient?
Should I add the capacitor you mentioned?”

[pito]

if diodes are ok ( not burned out ) then there is no needs to change resistors, your problem is in this area, add a capacitor as on the drawing, check DC voltage on both sides of the diodes ( betwin ground and diodes ), with coil and withouth coil.

[Jafar]

The diodes are dead , remove them and check them, the voltage over there should be 0.6Vpp, increase R6 to 1k.

“I increased R6 to 1 kΩ, but the peak‑to‑peak voltage didn’t change and remained the same as before. I even reduced the resistor to 500 Ω, but still nothing changed. I lowered it further to 330 Ω, yet again no change occurred.”

[Jafar]

so you check the diodes with an ohmmeter?
show the picture of the diodes area ( the other side pcb ), if diodes are ok then must be error on pcb.

“I checked the diodes with the diode tester and they are all fine. I also inspected the back side of the PCB according to the schematic, and there is no issue in that area.
In your opinion, is there any need to change the values of R5 and R6?
And do you think R6 might need to be moved after the diodes — meaning between the diodes and the preamp?

This issue is really driving me crazy.”

[Jafar]

so you check the diodes with an ohmmeter?
show the picture of the diodes area ( the other side pcb ), if diodes are ok then must be error on pcb.

I haven’t changed resistor R6 to 1 kΩ yet. I’ll change it and let you know.”

[pito]

so you check the diodes with an ohmmeter?
show the picture of the diodes area ( the other side pcb ), if diodes are ok then must be error on pcb.

[pito]

green trace is the output of the LF365 at pin 6,.

you have power supply +/- 12V so the output of the amplifier cannot be bigger than 24 Vpp, and you have over 100V

[Jafar]

The diodes are dead , remove them and check them, the voltage over there should be 0.6Vpp, increase R6 to 1k.

“I checked the diodes. Even when the diodes were 1N4148, the same voltage shown in the photos was present. Since this diode was made in China and not suitable for the coil’s instantaneous current, I suspected that this might be the reason the clamp circuit wasn’t working. So I replaced it with a Schottky 1N5819 to see if anything would change, but nothing happened. I tested the diodes and they are all OK.”

[pito]

post #66

The diodes are dead , remove them and check them, the voltage over there should be 0.6Vpp, increase R6 to 1k.

[Jafar]

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“These two images were taken separately, each with the same probe fixed on the point you mentioned, so that nothing changes between them.”

[Jafar]

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“At the input of my op‑amp I don’t have anything like that.
My positive voltage is lower than +12 V, but my negative voltage is much higher than −12 V, and sometimes it reaches close to −90 V or even mo