Step 4 signal looks wrong to me

[billr]

Not getting more than 120v and the signal looks like it's inverted to what it should be. From what I've seen the signal should go upwards in the form of a spike. Not like shown.

Have tried 470 and 680 resistors and a dampening tool but very little change from 200 ohm up to 1200 in the signal height.

Coil was taken from my Barracuda which works really well. Even made a coil from 1mm Cu wire @125mm radius as per the forum calculator. Both coils produced similar figures.

Swapped out the 555 and 1054 chips in case defective to no avail.

Any suggestions?

Defective IRF840 maybe?
Nothings getting hot when hooked up.

[Qiaozhi]

Not getting more than 120v and the signal looks like it's inverted to what it should be. From what I've seen the signal should go upwards in the form of a spike. Not like shown.

Have tried 470 and 680 resistors and a dampening tool but very little change from 200 ohm up to 1200 in the signal height.

Coil was taken from my Barracuda which works really well. Even made a coil from 1mm Cu wire @125mm radius as per the forum calculator. Both coils produced similar figures.

Swapped out the 555 and 1054 chips in case defective to no avail.

Any suggestions?

Defective IRF840 maybe?

Nothings getting hot when hooked up.

Are you sure you're making your measurements with reference to battery positive which is 0V in the MPP design?
This is mentioned at the top of page 4 under "Important Points".

[billr]

Yes the negative lead of the 10x probe is connected to TP5 and I'm testing the signal from the damping resistor hole in the pcb.
Can only get the wave to rise above the line if the voltage is set below 1v as shown. More than that and it shows as it is in the photo.
Also found that removing the coil wires from PL1 and 2 whilst running does nothing different. It's like the coil is not recognized.

[surfdetector]

Bill,
Post a picture of your coil connections both at the PCB as well as how you have connected your coil to your cable.
Thanks

[surfdetector]

Bill try clipping your probe around the insulated wire of the transmit lead and see what your signal looks like while leaving the ground clip attached to TP5

[billr]

Hey Surf
Its not a connection issue I'm certain of that. A continuity check from the coil cable ends checks out.
Did the same for SP1 and 2 following the PCB tracks and again I had good results.
I'm thinking it's either a bad part or the electronic gods just hate me.
There is only after all 7 parts in the step. three of which I know are good.
Have ordered another 840 in case. Will swap out the two resistors and diode whilst I wait.

Did your second suggestion before my first post. looks like it is not receiving power hence my doubt re the 840 or something in between.

[surfdetector]

What do you get at the cathode side of D7?

[Qiaozhi]

If you've connected your coil between PL1 pin2 and PL2 pin2, then it's not actually connected to the TX circuit. That's what it looks like to me in your photo.

The damping resistor needs to be connected across the coil, and as you can see from Fig. 7 this is connected between PL1 pin2 and 0V, so your coil needs to also be connected between PL1 pin2 and 0V. In that case connect your coil between PL1 pin2 and either pin1 or pin3. Then it should work.

Note that the MPP can use separate TX and RX coils. Once you have the coil connected between PL1 pin 2 and pin1/3, and checked that it now works, short PL1 pin2 to PL2 pin2. Study Fig.7 and it should be become clear.

[billr]

If you've connected your coil between PL1 pin2 and PL2 pin2, then it's not actually connected to the TX circuit. That's what it looks like to me in your photo.

The damping resistor needs to be connected across the coil, and as you can see from Fig. 7 this is connected between PL1 pin2 and 0V, so your coil needs to also be connected between PL1 pin2 and 0V. In that case connect your coil between PL1 pin2 and either pin1 or pin3. Then it should work.

Note that the MPP can use separate TX and RX coils. Once you have the coil connected between PL1 pin 2 and pin1/3, and checked that it now works, short PL1 pin2 to PL2 pin2. Study Fig.7 and it should be become clear.

Well this is embarrassing.
I've been looking at the board for a hour or two trying to figure out where the problem exists in so few parts and you spotted it in a second.
Now getting 0 to 380v flyback pulse and the signal looks as expected. Difficult to catch the pulses on my scope as they come and go. These are the best shots I could get.


Gonna go outside now and hit my head with a piece of 2x4. See if I can knock some sense into myself.
Sorry to waste anyone's time. And as always. Thank You.

[surfdetector]

The best problem to have is one that is easily sorted. Glad it's fixed.

[Qiaozhi]

Gonna go outside now and hit my head with a piece of 2x4. See if I can knock some sense into myself.

Glad to be of assistance.