Sniffer XR-71 help

[Jafar]

[Jafar]

Always start at the beginning, Make sure all power supplies are reasonably correct, nothing else will work without that.

Next task is to get D1a running. PR1 should vary the frequency but I don't know what the frequency range is on this project. When you have D1a running, then I assume D1b adjusts the pulse width via the 20k pot. Again, I don't know the proper range. All this should drive Q1 with a pulse train. This has to work correctly before moving on.

Then you will need to test the other pulses at test points P2, P3 to make sure they are working. Then start looking at signals down the analog path; P1, Tr6, Tr7, etc. All of this requires an oscope.



The cap on the control voltage pin is optional. It can help with jitter but it's not a big deal.

Hi Carl, how are you?
I’ve tested various points of the circuit using an oscilloscope and I’m sending you the images below. However, adjusting the SIGNAL (50k) and SENS (500k) potentiometers doesn’t seem to affect the pulse on D3 and D2.
Also, I have another question: does this device require the second section to function, or can it work without it? By the second section, I mean the microcontrollers PIC16F676 or PIC18F252.

Please help me — I’ve been struggling with this device for a month now.

[Jafar]

.

[Jafar]

Signal A —D1A , pin 5

Signal B —D1B , pin 9

Signal C —D2A , pin 6

Signal D —D2B , pin 10

Signal E —D3A , pin 6

Signal F —D3B , pin 10


[ATTACH]n442379[/ATTACH]

[Jafar]

"In D1B (NE556), the pulse width is adjusted by the NOISES (20k) potentiometer

[kt315]

Hi Carl, how are you?
I’ve tested various points of the circuit using an oscilloscope and I’m sending you the images below. However, adjusting the SIGNAL (50k) and SENS (500k) potentiometers doesn’t seem to affect the pulse on D3 and D2.
Also, I have another question: does this device require the second section to function, or can it work without it? By the second section, I mean the microcontrollers PIC16F676 or PIC18F252.

Please help me — I’ve been struggling with this device for a month now.

D3 and D2 doing delay. they are FIRST STROBE DELAY and SECOND STROBE DELAY tuning by the pots. you have to look them in relation to GATE pin signal on mos-fet.
FIRST STROBE DELAY is cutoff 'little - big' target. SECOND STROBE DELAY influences on a sensitivity and serves like a ground balance/tuning.

[Jafar]

D3 and D2 doing delay. they are FIRST STROBE DELAY and SECOND STROBE DELAY tuning by the pots. you have to look them in relation to GATE pin signal on mos-fet.
FIRST STROBE DELAY is cutoff 'little - big' target. SECOND STROBE DELAY influences on a sensitivity and serves like a ground balance/tuning.

Hi kt315,
I disconnected the device from the coil and realized that D2 isn’t working, and as a result, D3 isn’t functioning either. The signal does reach from D1 to pin 5 of D2, but D2 — which I used a CD4538BE for — doesn’t operate properly.

I bought a replacement for the CD4538BE: the CD74HCT4538E.
However, its operating voltage is lower, and I’m not sure how to reduce the voltages in the circuit to make it work.
Is it enough to just bring its VCC below 5 volts?

Please help me — I’m really stuck.

[kt315]

in my design i changed VD8 VD9 on 1N400x type. 1N4148's are burnt in customers bought boards. chinese made 1N4148's are poor on current.
do not desolder the diodes from board, check them by a tester on DIODE CHECK scale right in board.

[Jafar]

in my design i changed VD8 VD9 on 1N400x type. 1N4148's are burnt in customers bought boards. chinese made 1N4148's are poor on current.
do not desolder the diodes from board, check them by a tester on DIODE CHECK scale right in board.

If I replace those two diodes you mentioned with 1N400x types, do you think D2 and D3 will start working, or is it unrelated?
My D2 and D3 are CD4538BE ICs — do you have any thoughts on what might be preventing them from operating?

[kt315]

I DID NOT SUGGEST YOU TO REPLACE THE DIODES. i do that JUST IN MY BOARDS.

[Carl-NC]

First, KT is right, when you measure the pulses on D2 and D3 you need to use D1B-out as a reference so you can see how the delays vary. You have a 2-channel oscope, I hope it came with 2 probes.

But it looks like the pulses on D2 and D3 do not have enough voltage. Measure the voltage from +E to -E, it should be 10.5-10.8V. I assume it is because the D1 pulse voltage looks OK. You could replace VD8 and VD9 with, say, 1N4001 diodes but if the 4148's are working just leave them. It's possible the reset-hold from transistor T2 is not working right. Try disconnecting T2-pin1 (or, if easier, pull up one leg of R13) to disable T2, then see if the pulses start working.

You cannot use the 74HCT4538 with the 10.5V supply. If you reduce +E to 5V (just for D2 and D3) then the pulses will not have enough amplitude to drive D9 and D10. Then you would have to start redesigning the whole circuit to make it work.

I assume there is another schematic for a micro-driven display. You do not need it for the main circuit to work.

[Jafar]

First, KT is right, when you measure the pulses on D2 and D3 you need to use D1B-out as a reference so you can see how the delays vary. You have a 2-channel oscope, I hope it came with 2 probes.

But it looks like the pulses on D2 and D3 do not have enough voltage. Measure the voltage from +E to -E, it should be 10.5-10.8V. I assume it is because the D1 pulse voltage looks OK. You could replace VD8 and VD9 with, say, 1N4001 diodes but if the 4148's are working just leave them. It's possible the reset-hold from transistor T2 is not working right. Try disconnecting T2-pin1 (or, if easier, pull up one leg of R13) to disable T2, then see if the pulses start working.

You cannot use the 74HCT4538 with the 10.5V supply. If you reduce +E to 5V (just for D2 and D3) then the pulses will not have enough amplitude to drive D9 and D10. Then you would have to start redesigning the whole circuit to make it work.

I assume there is another schematic for a micro-driven display. You do not need it for the main circuit to work.

Hi,
I replaced the VD8 and VD9 diodes with 1N4007 because the original ones were burnt.
I measured the voltage between E+ and E−, and it was 10.12V. My battery is currently charged to 11.54V, so I’ll test again when it reaches 12V.
I haven’t yet tried the suggestion regarding T2, but I’ll let you know once I do.

[Jafar]

First, KT is right, when you measure the pulses on D2 and D3 you need to use D1B-out as a reference so you can see how the delays vary. You have a 2-channel oscope, I hope it came with 2 probes.

But it looks like the pulses on D2 and D3 do not have enough voltage. Measure the voltage from +E to -E, it should be 10.5-10.8V. I assume it is because the D1 pulse voltage looks OK. You could replace VD8 and VD9 with, say, 1N4001 diodes but if the 4148's are working just leave them. It's possible the reset-hold from transistor T2 is not working right. Try disconnecting T2-pin1 (or, if easier, pull up one leg of R13) to disable T2, then see if the pulses start working.

You cannot use the 74HCT4538 with the 10.5V supply. If you reduce +E to 5V (just for D2 and D3) then the pulses will not have enough amplitude to drive D9 and D10. Then you would have to start redesigning the whole circuit to make it work.

I assume there is another schematic for a micro-driven display. You do not need it for the main circuit to work.

Hi Carl,
I disconnected resistor R13, and now D2 and D3 are working — thank you so much!

What should I do next?

[Carl-NC]

The signal from T2 is what triggers the CD4538 and it may not be working correctly. Next thing I would do is look at the output signal of D4 and see if it is behaving as expected.

[Jafar]

The signal from T2 is what triggers the CD4538 and it may not be working correctly. Next thing I would do is look at the output signal of D4 and see if it is behaving as expected.

Hi Carl,
I checked D4 (LF357N) and took photos in two conditions — one with R13 disconnected and the other with it connected. I captured the signal from pin 6 of D4 in both cases.


R13 not connect


R13 connect

R13 not connect & coil connect

R13 connect & coil connect