Sniffer XR-71 help

[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.”

[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]

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

[pito]

Should be enough, DC voltages on diodes ?

[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]

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

[Carl-NC]

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

[Jafar]

[QUOTE=Carl-NC;n445520]

[QUOTE=kt315;n445515]


Hi KT315 and Carl-NC, Hope you’re doing well, friends.

After putting the snifferxr71 project aside for a while, I’ve started working on it again.
My clamp circuit is now working correctly — the mistake I had before was improper use of the oscilloscope, because I wasn’t connecting the scope’s ground to the circuit ground.

Now the problem I’m facing is with the preamp (LF357).
Everything looks good up to the preamp input, but the op‑amp does not produce a proper output, and the waveform is nothing like the preamp signal shown in the Hammerhead project or in the pulse detector example from Carl’s book.

The device frequency is 108 Hz.

One modification has been made in the project:
I disconnected pin 1 of T2: BC546, because it was causing interference with IC D2a (4538. I did this based on Carl’s advice.

I’d appreciate any guidance on what might be causing the LF357 output issue.

[Jafar]

[QUOTE=kt315;n445515]
Hi

[kt315]

One modification has been made in the project:
I disconnected pin 1 of T2: BC546, because it was causing interference with IC D2a (4538. I did this based on Carl’s advice.

Interference? are you reliant? Carl can advices what he wants. T1 and T2 is a circuit OVERLOAD PROTECTION. they turn up on big metal and moving strobes (there are two strobes) at right side of delta pulse, with more lowest amplitude. a signal after 357 is left low, in range of norma do not causing distortion of SAT part, D5 D7 etc.

[Jafar]

[QUOTE=kt315;n451358]

"When T2: BC546 is connected to D2, it causes D2 and D3 not to work. But when I disconnected it, following Carl’s advice, they started working."

[Jafar]

One modification has been made in the project:
I disconnected pin 1 of T2: BC546, because it was causing interference with IC D2a (4538. I did this based on Carl’s advice.

Interference? are you reliant? Carl can advices what he wants. T1 and T2 is a circuit OVERLOAD PROTECTION. they turn up on big metal and moving strobes (there are two strobes) at right side of delta pulse, with more lowest amplitude. a signal after 357 is left low, in range of norma do not causing distortion of SAT part, D5 D7 etc.

When T2: BC546 is connected to D2, it causes D2 and D3 not to work. But when I disconnected it, following Carl’s advice, they started working."

[kt315]

i do not understand you. BC546 is not connected to D2. give your schematic.

[Jafar]

i do not understand you. BC546 is not connected to D2. give your schematic.

marked the connection of T2: BC546 to D2 with a red line.”

[kt315]

ok. you mean the micro. on my schematics I use another specs for the micros.
reminder, DP is very sensitive PI, almost working in static mode. the disbalance by the overload signal goes to disbalance of SAT end circuit burnt continious sound.
but at table, not in field, you can disconnect the part, while it does not influence on good job.
i think you have something metallic around coil that you do not want to notice. your coil must be hold at half of heights of your room at the rope and be vertically. a distancy to room walls >>> 2 meter.
while your coil lies on the table with metallic inserts at bottom and you get the overload constantly.