HammerHead Problem

[surfdetector]

Hopefully this works.
Here are the photos of my board, I hope it helps. You can see we have different resistors installed and jumpers. Maybe your double front end has caused you to change these I dont know but hope you get it going!


[ATTACH]31460[/ATTACH][ATTACH]31461[/ATTACH][ATTACH]31462[/ATTACH][ATTACH]31463[/ATTACH]

I realize that it is now 6 years later, but I wanted to thank you for posting those pictures. They are really helpful.

[6666]

Not a problem!

I found my problem, R10 was open! I know I measured it when I installed it.
I'm not sure if it popped due to excessive voltage or just failed when the leads
were bent but we are back in business. I am going to go back to the active
shut off and 2 stage gain as I think it will make a faster detector!

Thats unusual , but you found it.

[Silver Dollar]

So I went back to active turn off and she works! The min delay from TX off seems to
be 13 us;


With 470 ohm damping resistor she rings a bit;


With 390 a little less ringing;


I guess I'm going to have to make a damping resistor setup to find the right value.

It transmits and receives but still no sound too so more troubleshooting is in order.

[Silver Dollar]

Not a problem!

I found my problem, R10 was open! I know I measured it when I installed it.
I'm not sure if it popped due to excessive voltage or just failed when the leads
were bent but we are back in business. I am going to go back to the active
shut off and 2 stage gain as I think it will make a faster detector!

[godigit1]

Thank you I could not find that in the document and explains why D5 doesnt work on my board. Cool Ill play with that.
Im learning still and trying to teach myself electronics (almost a year now) so sorry for the lame questions I may ask.
Also thanks for all your posts you devote allot of time to the forum.

[Silver Dollar]

Well R52, 53, 54 are for the low battery circuit. Many people leave them off.

[godigit1]

I know you set your board up differently than the standard VCO option. What are you using R52,53.54 to accomplish on you board? If I were to install them on the standard VCO set up would I gain any benefit?
I learn allot from threads like this.
Thank you all.

[Silver Dollar]

I'll have a look today. I tried 2 different FETs so have to imagine the problem is elsewhere...

[Chet]

Hi Silver Dollar, since you have a drive pulse on the Gate and have already replaced the MOSFET. There may be problem with the positive 12v from the battery getting through the circuity to the Drain. Or the negative 12v side may not be getting to the Source of the MOSFET.


With the battery removed and the power switch on; measure continuity from the positive battery connection to the cathode of D10; it should read the resistance of the coil; check D10 front to back resistance and insure that it is installed correctly.


From the negative side of the battery measure continuity to the Source of the MOSFET; it should read the 1 ohm resistance of R10.

[mickstv]

Gate drive looks ok. More than likely the Mosfet is faulty.

[Silver Dollar]

I hadn't tried looking at the drain as I assumed there would be high voltage there;
Gate


Looks like it's not firing;
Drain

[mickstv]

SD can you post up a CRO pic with the CRO lead connected connected directly to the gate of the Mosfet and also a a pic with the cro lead connected to the drain of the mosfet.

[Silver Dollar]

Well it's 50 us wide and repeats at 1 khz it should be OK...

[6666]

SD are you happy with the pulse from the 555 ?

[Silver Dollar]

Well I went back to the passive turn off and one gain stage. I left the gain at 33 for now.
I still get the wrong thing for the recieve wave. It looks lit the current signal as I do not
see the TX voltage. I'm stumped. I tried 2 FET's, 2 Coils and active/passive turn off...