Rev-E build (issue) step 5

[Cyclotron]

Hey all, I'll get straight to it. I've got MPP issues.

I followed the guide, and everything was working as intended, testing each stage as per the guide, unit's completed but all I get a slow "click click click click click" from the thing, when i put a pair of pliers on the coil for 3-4 seconds the "click click stops, when i move them away i get the clicky click click back, but yeah something is not right, and i'm damned if i can figure it out.

I went back through the steps and I was just testing Step 5 scope on TP3. RX pre-amp, when i connect the scope, i get this mess.

REALLY hard to nail down a trigger on that bunch of fuzz..

Any thoughts on the cause this kind of noise? bad NE5532 ? i don't have one on hand to swap out but ordered a bunch just in case.

[waltr]

Guessing the period of high without noise is during the TX ON pulse.
The Noise looks like the pre-amp may be oscillating (recheck all connections and soldering)
OR
There is huge EM noise in your workshop.

Did you try taking the detector outside away from AC mains and other electrical equipment?

[kt315]

at first stage use microcoil (pinpointer tipo). that will notably decrease all EMFI on it, be cause effective receive coil square is also smallest.

[Cyclotron]

Guessing the period of high without noise is during the TX ON pulse.
The Noise looks like the pre-amp may be oscillating (recheck all connections and soldering)
OR
There is huge EM noise in your workshop.

Did you try taking the detector outside away from AC mains and other electrical equipment?

I will test the detector away from power sources tomorrow morning, and check all the soldered connections, though i did that earlier

I recently built the Mirage PI Clone PI and hammerhead and didn't have any EM noise issues, but they're different beasts, so who knows.. So frustrating!

Thanks for the hints. keep em coming

[Cyclotron]

at first stage use microcoil (pinpointer tipo). that will notably decrease all EMFI on it, be cause effective receive coil square is also smallest.

I will construct and try a micro coil tomorrow also, thanks.

[kt315]

no construct. take erase head from old tape magnetophone. it is 200-300uH. good for usage.

[Qiaozhi]

Hey all, I'll get straight to it. I've got MPP issues.

I followed the guide, and everything was working as intended, testing each stage as per the guide, unit's completed but all I get a slow "click click click click click" from the thing, when i put a pair of pliers on the coil for 3-4 seconds the "click click stops, when i move them away i get the clicky click click back, but yeah something is not right, and i'm damned if i can figure it out.

I went back through the steps and I was just testing Step 5 scope on TP3. RX pre-amp, when i connect the scope, i get this mess. [ATTACH]50748[/ATTACH]

REALLY hard to nail down a trigger on that bunch of fuzz..

Any thoughts on the cause this kind of noise? bad NE5532 ? i don't have one on hand to swap out but ordered a bunch just in case.

This might an obvious question ... but you do have a damping resistor across the coil?

[Cyclotron]

I do have a damping resistor on the coil yes, I've tested multiple, from 270 ohm up to 470 ohm, does not solve the problem sadly.

[Qiaozhi]

I do have a damping resistor on the coil yes, I've tested multiple, from 270 ohm up to 470 ohm, does not solve the problem sadly.

The preamp output can also look like that if the coil is disconnected, together with the damping resistor. Do you have the correct wiring between PL1 and PL2? (See Fig. 7 - Coil Configurations)
PL1 pin2 must be connected to PL2 pin2 for a mono coil. The link should be made in the coil plug between pins 1 and 5.
A common error is to leave out this link.

[Cyclotron]

The preamp output can also look like that if the coil is disconnected, together with the damping resistor. Do you have the correct wiring between PL1 and PL2? (See Fig. 7 - Coil Configurations)
PL1 pin2 must be connected to PL2 pin2 for a mono coil. The link should be made in the coil plug between pins 1 and 5.
A common error is to leave out this link.

Okay that might be my issue, That diagram never made sense to me for this reason, If you've got Rx and Tx connected to the coil then in theory you've already achieved this connection, maybe i'm missing something but wouldn't connecting pins 1-5 just short out Rx to Tx before the signal reaches the coil?


Example of super technical high quality drawing lol

[Qiaozhi]

Okay that might be my issue, That diagram never made sense to me for this reason, If you've got Rx and Tx connected to the coil then in theory you've already achieved this connection, maybe i'm missing something but wouldn't connecting pins 1-5 just short out Rx to Tx before the signal reaches the coil?


Example of super technical high quality drawing lol [ATTACH]50751[/ATTACH]

I will see if I can explain:
There are two wires that go to a mono coil - the hot wire, and the screen. They are not called TX and RX.
Connect the hot wire to PL1 pin2, and the screen to either PL1 pin1 or PL1 pin3. Now the transmitter will work, but there will be no signal received by the preamp because there is nothing connected to PL2 pin2. The two connectors are to allow the use of an induction balanced coil with separate TX and RX loops. For a mono coil you need to short PL1 pin 1 to PL2 pin1, otherwise the detector will not be able to detect anything. You can do that at the PCB or the coil connector, although it is better to do this at the coil plug in case you decide to use an IB coil at a later date.

[Cyclotron]

Oh man that makes perfect sense now.. Quite a bit different from most of the other PI kits i've built

Thank you so much Qiaozhi.

[surfdetector]

I will test the detector away from power sources tomorrow morning, and check all the soldered connections, though i did that earlier

I recently built the Mirage PI Clone PI and hammerhead and didn't have any EM noise issues, but they're different beasts, so who knows.. So frustrating!

Thanks for the hints. keep em coming

It might be helpful to post a couple of good pictures of the front and back of the PCB, sometimes other sets of eyes can catch things. A picture of your coil connection to the board would also be good.
Cheers

[Qiaozhi]

It might be helpful to post a couple of good pictures of the front and back of the PCB, sometimes other sets of eyes can catch things. A picture of your coil connection to the board would also be good.
Cheers

I think we've figured out what was wrong. The connections at PL1/PL2 were incorrect.

[Cyclotron]

Correct, I'm pretty sure it is the incorrect coil connections, i will test it after work, side note, I am running a Minelab 8" mono coil.