Sniffer XR-71P Rev 1.3/1.34 NOOB Help

[Fugazi]

Hello All,

Picked up a box of parts off a Treasure Net guy, 3 assembled PCB's (2=Rev_1.3 and 1=Rev_1.34) and a few bare PCB's in box

I knew it wasnt going to be plug and play but I needed a winter project

Wound a test coil, used CAT5 wire (0.5mm ?) and made a 12" diameter coil 18T for a total resistance = 2 Ohm (side note, 5gal buckets make great coil templates since the bottom has a draft angle to it)

Soldered 2 Ohm resistor in series for a total of 4 Ohms coil resistance

Rev 1.34 board observations (see .jpg with my red mark ups for location/print):
1) Some missing components
1.a) Damping Resistor
1.b) 1N4148 diode
2) Incorrect components (The silk screen on bare PCB show one value but schematics I've found on here call for another
2.a) 680k or 68k?
2.b) 680k or 180k?
2.c) 12k or 11k?
2.d) TL082 or TL072?

Problem Statement:
1) I am getting tone only when turning GAIN and/or THRESH pots up, bringing metal object near coil doesn't seem to produce change in tone
1.a) DC current at 12v is ~50mA, MOSFET is cold
2) There are two trimmer pots, how do I set them? I have not touched them for now

Questions:
1)I will not have access to a scope until next Tuesday, are there any easy checks I can do with basic multimeter?
2) Should I just kick this project to the curb and start with a fresh hammerhead PI build or are there advantages to staying on this platform?



Once I have a multimeter I can check pulse according to diagram (see link below)


Pics can be seen here: https://drive.google.com/drive/folde...94?usp=sharing


Thanks for any breadcrumbs to help keep me on the trail

[kt315]

Questions:
1)I will not have access to a scope until next Tuesday, are there any easy checks I can do with basic multimeter?
----
i especcially had bought https://www.banggood.com/Orignal-JYE...r_warehouse=CN
and will show the tips using this type of portable. you can not check impulse signal by basic multimeter. the basic multimeter
measures just AC clear sinusoidal signal and clear DC level.

[Fugazi]

Ordered the suggested mini-scope, i like the price - thank you for the suggestion

Next week I can hook up to scopes in our lab at work

[kt315]

this forum has whole information you ask, but people do not wish to learn search engine possibility and seeking what they need (the their laziness).
so i do not want to put the same files back because the Sizif's job.

load and unRAR https://dfiles.ru/files/iku2hsz05?redirect
open folder PCB from Gueorgui mustang XR71

[Fugazi]

Thanks for the information, very helpful files in that package

I think it would be best for me to start with the MPP - I ordered a kit from Silverdog

I'll save my XR71 project for round 2 if needed

I dont need anything special like Delta Pulse, just need to be able to use 1m or larger coil and be towed behind small boat in shallow fresh water. I think MPP can meet my needs

[homefire]

BangGood is offering those DSO 150 Pre Constructed with proper 10X Probe for only $25.00 right now.

[dbanner]

I see chips are soldered directly on PCB, that makes for difficult life ahead for you. Make sure you have full luxurious head of hair.
Sockets allow for much easier task for removing/ replacing chips should the need arise. You would have to assume these boards were tested ok, without oscilloscope, only expert engineer who knows about pulse metal detector can close his eyes and troubleshoot the problem.
You will have same problem with any other build, minipulse, hammerhead etc. Very rare the damn thing works at first switch on(with several hundred soldered joints and over hundred components and many, many steps to follow, assume just a single error will cause thing not to work). Good quality multimeter and little DSO scope is a must for setting up the thing once you get it working.
P.S. Good idea to have some means of limiting/ monitoring current consumption so as to avoid magic smoke at first run.

[Fugazi]

dbanner, I lost my hair early since I always choose to do things the hard (cheap) way. In the end it may or may not work but I always learn something

Before I waste money and jump platforms to MPP I wanted to give this thing a proper scope inspection

I have a timing diagram for XR71 from KT315's info dump



When compared to my scope measurements I have an issue with TR3 (Gate leg at FET) - the timing diagram shows alignment with TR2

The timing measurement shows TR3 behind TR2 :: Yellow=TR2 and Blue=TR3



I then checked triggers of pin6 and pin8 of 556 chip and there is a relationship but I dont know if its correct or not....This is where my foundation knowledge and experience is lacking

Green=pin6 or 8, Yellow=TR2, Blue=TR3, Pink=TR4

pin 6



pin8




Question: Are TR3 and TR2 supposed to be aligned (rising edge)?

If so, what are the best guesses as to why it is delayed (trigger or threshold or other???)

All the other signals look pretty good, spacing and width are adjustable by potentiometers

Thank you all for the input

[kt315]

I have a timing diagram for XR71 from KT315's info dump
Correct diagram_by_Geo.gif
---
sorry you are operating by very old data diagram that was corrected many many years ago by russians.
so i could not share this diagram neverwhere.
right one was posted 1000th times but as you are newibie for the forum you do not wish actively
to use advanced research knob (laziness maybe).

[Fugazi]

Thank you for the update, diagram looks more like what I measure

I've spent >16hrs researching this platform, laziness is not my style. Laziness could only be claimed when someone fails to present measurements or follow other direct suggestions

There is 10yrs of information across a 1000+ posts, trying to find the line of truth inside a meatball of data one of the challenges

Maybe in the future, when (if) my pcb is operating as designed I will be able to help other newcomers as the group has helped me thus far

Thanks again, now I move onto next issue: Why is system drawing 2A current when 18T 30cm diameter 2 Ohm test coil attached?... I will measure inductance and maybe make another coil to proper specs before continuing to debug

[dbanner]

Nevermind about kt315, he is lovable character here on forum, a bit like Grandpa of geotech forum.
Now there is issue on schematic with collector of transistor T2 connection to U3A pin 2. I wish someone could remind me of its purpose.

[kt315]

thanks DB. x)))

do not see U3A... can you reformulate your request using my schematic?

http://ipic.su/img/img7/fs/DP_sch31.1550237343.gif

[dbanner]

thanks DB. x)))

do not see U3A... can you reformulate your request using my schematic?

http://ipic.su/img/img7/fs/DP_sch31.1550237343.gif

Sorry, I meant to say D2A, the 4538 chip. My Delta timing pulses not work unless I disconnect collector of transistor T2. I can't find reason for this condition.

[kt315]

VT2 VT3? this circuit is some kinda a protection against overloading (big target + very small distancy coil-target).
how it is working. the first (and second too) strobe is MOVING AT RIGHT SIDE of the diagram, in the side OF LESS of
amplitude of delta pulse. so overloading is getting impossible (or near that).

Figaze has to show that i tell. just bring big metal to coil and you will see this effect.

[dbanner]

Thanks for the explanation. But can't get it to work as described. I'll put it aside for the time being.