Sniffer XR-71 help

[kt315]

R13, T2, T3 is a part doing overloading protection. you can see its work just with a coil, with a metalic near it you will move it to the coil and back, look how FIRST STROBE (Tr4) will move at right side from some moment, on your scope, D1B-out as a reference.

without coil and without metal piece you will see nothing.

[Jafar]

R13, T2, T3 is a part doing overloading protection. you can see its work just with a coil, with a metalic near it you will move it to the coil and back, look how FIRST STROBE (Tr4) will move at right side from some moment, on your scope, D1B-out as a reference.

without coil and without metal piece you will see nothing.

Thanks for your guidance.
When I disconnect R13, D2 and D3 work, but when it's connected, they don't.
To check what you mentioned, should I connect R13 or leave it disconnected?
And where exactly should I place the second probe to observe the FIRST STROBE in the circuit?

[kt315]

meant you have a trouble in this circuit. check T2 T3 and pinouts of the transistors. you have be confident one is PNP second is NPN and they sure soldered in their places right.
FIRST STROBE is Tr4 output.

[kt315]

follow this pic

[Jafar]

meant you have a trouble in this circuit. check T2 T3 and pinouts of the transistors. you have be confident one is PNP second is NPN and they sure soldered in their places right.
FIRST STROBE is Tr4 output.

I’ve checked the transistors T2 and T3 — there’s no mistake in their pinouts or types.
But as long as R13 is connected, I don’t see any signal from D2 and D3.
Could you please guide me?

[kt315]

something wrong in your pcb but i can not help. you have to check all resistors and voltage polarity of supply. this part is working perfectly, no need to delete R13.
give an o-scope pic D4 pin 6 again.

[kt315]

neutral part of the pre amp output signal is zero, that i do not see in your pics.

[Jafar]

something wrong in your pcb but i can not help. you have to check all resistors and voltage polarity of supply. this part is working perfectly, no need to delete R13.
give an o-scope pic D4 pin 6 again.

[kt315]

reference point is GND, output of D6A. THE level you have to do the measuring vs.

[Jafar]

I used a 22.5-ohm resistor in series with the coil for damping.

[kt315]

abnormal signal. huge. it is not limited by the diodes VD3 VD4. 'delta pulse' must be approx 2V P-P. not more.

[Jafar]

something wrong in your pcb but i can not help. you have to check all resistors and voltage polarity of supply. this part is working perfectly, no need to delete R13.
give an o-scope pic D4 pin 6 again.

I didn’t remove R13 — I just disconnected one of its legs, as suggested by Karl. When it was disconnected, D2 and D3 started working.
But when the part of the circuit with T2 and T3 is connected to pin 2 of D2, D2 and D3 completely stop working.

If you need photos of any part of the circuit, I can check and send them to you.

[Jafar]

abnormal signal. huge. it is not limited by the diodes VD3 VD4. 'delta pulse' must be approx 2V P-P. not more.

The device is connected to the coil.
If you think the diodes might be faulty, I’ll replace them.

[kt315]

D2 and D3 completely stop working.

your circuit is overloading by DC component on preamp output. Overloading Protection circuit works, T2 is open.
in normal mode Overloading Protection circuit must be turn off.

[Jafar]

D2 and D3 completely stop working.

your circuit is overloading by DC component on preamp output. Overloading Protection circuit works, T2 is open.
in normal mode Overloading Protection circuit must be turn off.

Do you have any recommendations for resolving this issue? Which parts should I inspect?