Oscilloscope bandwidth and multi turn presets, questions

[nonkapo]

As you are continuing if not yet finished, look at the video in post number 6 of the following thread: https://www.geotech1.com/forums/show...ion-(of-mine-)).
Will help you to clear any doubts. Good luck.

[Denots]

As you are continuing if not yet finished, look at the video in post number 6 of the following thread: https://www.geotech1.com/forums/show...ion-(of-mine-)).
Will help you to clear any doubts. Good luck.

Thanks that might help me troubleshoot, completed it but part Q2 which is a transistor IRF840 is overheating and starts to smoke.
After watching the video in that thread I think I may have been going about it all wrong, it all looks right till about step 4, I thought I was doing it right but not convinced now, I’ll go back through it later and compare to the video and see if I can figure anything out.

[nonkapo]

Do you have the coil atached or not?

[Denots]

When the coil is attached is when the transistor gets hot, if I run the circuit with no coil the transistor stays cool

[nonkapo]

Note the video is not for the E revision,so there might be some differences. Are you following the geotech manual as well? What about the coil measurements? Within specs?

[Denots]

Note the video is not for the E revision,so there might be some differences. Are you following the geotech manual as well? What about the coil measurements? Within specs?

Yes followed the manual to the best of my abilities, Positive and negative voltage is all new to me and I know I forgot about tp5 being used as 0v, I have been clipping the ground on the oscilloscope to the outer pins of the battery connection at pl4, I’m wondering if this would have caused any issues, I’ll have to go back and sit down start at step one and check through everything again and double check my results.
the coil I have built using a calculator so just assuming it’s right, I have a tester on order just waiting on that before I can find out the true inductance of the coil.

[waltr]

Yes, the Battery Positive as the 'COMMON" or "ground" is confusing at first,

Print out a copy of the schematic and with colored markers note where the "common' is. A green marker is good so high light all the lines that connect to battery positive in green. Then mark the other Voltages with a different color.

Or, redraw the basic circuit to help get a better understanding of the Voltages as they relate to the "common".

You must also ensure that the circuit is Never connected to Earth ground (AC Mains). Best to power from a battery, with Good Current limiting like an automotive tail light bulb in series.

Most of the PI detectors will run fine on a wide range of coils. So any coil with 300 to 500uH inductance will work for testing.

[nonkapo]

As it is mentioned many times on this forum, never get anything for granted. Check the values of the components meticulously. Make sure the active components pin out is as described, especially when using substitutes. You can see somewhere photo of diode marked wrong way and i just get in to situation where fet transistor's pins are not matching the pin out in the manufacturer datasheet. Better take a bit longer to assemble and do it right, rather than getting disappointed. Thrust me even experienced guys here have done such mistakes,what about someone who's new. Experience shows that with the proven working designs, most of the problems come from fake components, wrong values or insertion with wrong pin outs. Good luck.

[dbanner]

Put a heatsink on the MOSFET. When you've got the circuit working right, it should run cool, or only slightly warm, then you can dispense with the heatsink if you wish. Excessively high temperature can potentially degrade or damage the MOSFET.
Drill a hole in any old piece of chunky aluminum or just anything you have at hand, put it onto MOSFET with small nut and bolt.
I don't expect you will have heat sink compound and wafer, but that's another story. This is only meant to be a temporary measure to provide some thermal protection for MOSFET.

[green]

Yes followed the manual to the best of my abilities, Positive and negative voltage is all new to me and I know I forgot about tp5 being used as 0v, I have been clipping the ground on the oscilloscope to the outer pins of the battery connection at pl4, I?m wondering if this would have caused any issues, I?ll have to go back and sit down start at step one and check through everything again and double check my results.
the coil I have built using a calculator so just assuming it?s right, I have a tester on order just waiting on that before I can find out the true inductance of the coil.

What is your coil diameter__________, wire size___________ and number of turns___________ ? Bundle wound?

[Denots]

Yes, the Battery Positive as the 'COMMON" or "ground" is confusing at first,

Print out a copy of the schematic and with colored markers note where the "common' is. A green marker is good so high light all the lines that connect to battery positive in green. Then mark the other Voltages with a different color.

Or, redraw the basic circuit to help get a better understanding of the Voltages as they relate to the "common".

You must also ensure that the circuit is Never connected to Earth ground (AC Mains). Best to power from a battery, with Good Current limiting like an automotive tail light bulb in series.

Most of the PI detectors will run fine on a wide range of coils. So any coil with 300 to 500uH inductance will work for testing.

Mine is being powered from a dc bench power supply, I set it to 12v and it pulls about 1amp from what I can remember, could it be my power supply causing problems?
I’ve never seen anything like it, just thought there was positive and negative and that’s all there is too it. That’s a good idea with the schematic though I’ll give that a try

As it is mentioned many times on this forum, never get anything for granted. Check the values of the components meticulously. Make sure the active components pin out is as described, especially when using substitutes. You can see somewhere photo of diode marked wrong way and i just get in to situation where fet transistor's pins are not matching the pin out in the manufacturer datasheet. Better take a bit longer to assemble and do it right, rather than getting disappointed. Thrust me even experienced guys here have done such mistakes,what about someone who's new. Experience shows that with the proven working designs, most of the problems come from fake components, wrong values or insertion with wrong pin outs. Good luck.

your right I should have spent more time testing components and things before fitting, next time round I’ll do things a little differently, some of these components I had trouble even identifying at first, like those box capacitors, never seen one in my life and the confusion in trying to work out what was what lol.

Put a heatsink on the MOSFET. When you've got the circuit working right, it should run cool, or only slightly warm, then you can dispense with the heatsink if you wish. Excessively high temperature can potentially degrade or damage the MOSFET.
Drill a hole in any old piece of chunky aluminum or just anything you have at hand, put it onto MOSFET with small nut and bolt.
I don't expect you will have heat sink compound and wafer, but that's another story. This is only meant to be a temporary measure to provide some thermal protection for MOSFET.

That’s a good idea, I’ll give that a try, might just help keep it cool enough till I can figure out what’s going on.

What is your coil diameter__________, wire size___________ and number of turns___________ ? Bundle wound?

I’ve used two core bell wire to knock up a test coil, 20 winds with two cores so 40, wrapped into a flat disc, I can’t remember the measurements but according to the calculator should be somewhere near spec, waiting on a test device so I can find out exactly what the inductance is

[nonkapo]

No worries, once you get you chinese device it not only measure inductance but can check bipolar and fet transistors(and showing their pinouts), any type capacitors(and their ESR) and so on. Very helpful. It even have a generator and frequency counter. Not all measurements are absolutely accurate but for that price it does fairly well.

Regarding the coil it does not sound well. What's the gauge first? The way i understand your winding's are parallel so you have less resistance but not appropriate inductance. For beginning best is to try spiral coil from 24awg speaker cable wound over CD spindle. Easy to wind. Also not bad idea is to try with small coil first and than go for bigger and more complicated one.

[waltr]

Mine is being powered from a dc bench power supply, I set it to 12v and it pulls about 1amp from what I can remember, could it be my power supply causing problems?
I?ve never seen anything like it, just thought there was positive and negative and that?s all there is too it. That?s a good idea with the schematic though I?ll give that a try

A constant (averaged) 1 Amp sound too high. My HH which has similar circuits draws less than 200mA when running.
Are all the timing circuits pulsing correctly?

Regarding the coil it does not sound well. What's the gauge first? The way i understand your winding's are parallel so you have less resistance but not appropriate inductance. For beginning best is to try spiral coil from 24awg speaker cable wound over CD spindle. Easy to wind. Also not bad idea is to try with small coil first and than go for bigger and more complicated one.

Yes, a smaller simple coils is all that is needed to test circuit.

[Denots]

Finally had a bit of time today and managed to get my circuit out. here are my findings, personally I think I may have blown the transistor or something as everything is way out now.
Firstly with just the power supply connected and set to 12v the circuit draws 0.05a and transistor Q2 (IRF840) stays cool.
All tests were done without coil or any plug in variable resistors connected.
Step 1- with multimeter across u3 pin 4 and tp5 I get 5v which is good.
Step 2- with multimeter across tp5 and tp7 I now get 0.7v, it used to be 6v but for some reason now it?s dropped.
Step 3- connect oscilloscope probe earth clip to tp5(0v) and bench power supply shoots up to 1.44a draw

oscilloscope with earth clip connected to negative battery terminal and probe on u9 pin2 still produces a wave but no other test points produce any form of wave, whereas before I was getting a wave that I could adjust with the 3 potentiometers.

All steps up to 4 were completed and working fine as long as I kept my oscilloscope ground clip connected to battery - I?d get the readings described in the manual.
after step 4 I felt a bit out of my depth but thought it was working ok, flyback voltage in step 5 took a bit of time to figure out but from what I could work out it was 320v presuming I was doing it right, step 6 onwards was all a bit alien to me and I bumbled through it.
Was all giving me waves though when I was checking the test points.
Maybe the transistor overheating from something I did wrong has caused an issue, when my test tool turns up I?ll start checking components and see if I can narrow it down a bit, till then I?ll probe around with my multimeter and see if I can find anything comparing it to the schematic

[Denots]

Actually I think the mosfet might be ok, multimeter in diode mode, red lead on centre leg black lead on either outer leg produces no result
black lead centre and red lard left leg gives me 1347, red lead on right leg gives 526.
So with my limited knowledge it would appear that the mosfet isn?t the problem.
Just discovered if I put my multimeter across the centre pin and either of the outer pins of pl1 the tx plug I get zero resistance, that would mean there is a short somewhere or maybe a blown component?

edit:
damping resistor r4 has no resistance