Hammrehead Problem Poor detection and No effect on threshold.

[Sebastos34]

Hi all!

Some years ago, I have started the Hammerhead project, but after spending a lot of time to try make it work without success, I had abandonned.
Now, I have take out the PCB and fond some wiring problems on it.
It's now basically working, but only with big metallic objects.
Some problems : On my circuit I can't null TP4 with P18, and Threshold have no effect. Sensitivity have minor effect too.

I have try to move all pots, but the best that I obtain, is 20-25Cm with a metallic stapler, and only 1 Cm with a big coin.
My coil is 500?H and about 1.5 Ohm, not shielded.

Here is a PIC of my PCB. (dont pay attention to NE5534 I have adapted a SOIC8 format the time I receive a DIP8 one.)



Of course I have a multimeter and an oscilloscope (35V MAX with X10 probes).
Any help will be apprecied.
Thanks!!!

[waltr]

Coil should be in uH (microHenry), 500uH is slightly high but should work fine.

What is the sample Delay? If too long then only large objects detected.
Coil Damping?? Show us a scope picture on Preamp out (TP4) with TX pulse (TP1) Trigger on TP1.

What is the TX pulse width? Measure at TP1 with scope.

Put DVM on Pot R18 wiper and ensure it changes when turning pot. A little math (Voltage dividing) will tell you what Voltage range you should see.
Do the same for the Threshold Pot, R31.

Did you install R22 and/or C16? I found these didn't help so R22 = zero Ohm and C16 not installed.

With a 35V MAX scope probe DO NOT put it on TP2, the coil, which can have hundreds of Volts fly-back.

Put scope on TP9 (Sat output) to check response. If good here to smaller objects then could be issue in next stages.

[Sebastos34]

Hi Waltr, and many thanks for your help!

For the Coil its uH effectively (the forum don't accept the "micro" font).

Here are some pics of differents test points :
This is for TP1 upside and TP4 at the bottom



This is TP1 and TP9

Seems that something is bad...

For R31 I have 0.4V/1.28V CCW and -1.28/-2.32V CW R35 Varies between -3.45V and 0.

For TP2, you don't think that it's OK with the X10 attenuator probe? That permit 350V I think.

P.S. : Sorry for my English, I'm French.

[Carl-NC]

TP4 is definitely wrong. My first thought was R10... it looks like you have the right value but check the solder joints, they look iffy. Probe the gate on Q3, the little jumper next to Q2 is convenient. You should get a nice pulse that looks like TP1 upside-down.

[Sebastos34]

Hi, Carl thank you too for your help!
I finally have find time to make some more tests.
I've just see that the fist photo I've sent is not good. Not the same scale for TP1 and TP4. Here is the correct photo:

For Q3 Gate, you can look that here:

As now the scale is the same it seems not good...
For R10 I have resoldered it and some other components, but not better...

Have you got any idea?

Thank you again Waltr and Carl!

[surfdetector]

Hi, Carl thank you too for your help!
I finally have find time to make some more tests.
I've just see that the fist photo I've sent is not good. Not the same scale for TP1 and TP4. Here is the correct photo:
[ATTACH]54998[/ATTACH]
For Q3 Gate, you can look that here:
[ATTACH]54999[/ATTACH]
As now the scale is the same it seems not good...
For R10 I have resoldered it and some other components, but not better...

Have you got any idea?

Thank you again Waltr and Carl!

Do you have a coil connected? Your TP4 is wrong. Can you post a picture of TP2?

[Sebastos34]

Hi Sufdetector, yes I have a 500uH coil connected. I give you a picure of TP2 ASAP.

[h9361]

Hi all!

Some years ago, I have started the Hammerhead project, but after spending a lot of time to try make it work without success, I had abandonned.
Now, I have take out the PCB and fond some wiring problems on it.
It's now basically working, but only with big metallic objects.
Some problems : On my circuit I can't null TP4 with P18, and Threshold have no effect. Sensitivity have minor effect too.

I have try to move all pots, but the best that I obtain, is 20-25Cm with a metallic stapler, and only 1 Cm with a big coin.
My coil is 500?H and about 1.5 Ohm, not shielded.

Here is a PIC of my PCB. (dont pay attention to NE5534 I have adapted a SOIC8 format the time I receive a DIP8 one.)

[ATTACH]54966[/ATTACH]

Of course I have a multimeter and an oscilloscope (35V MAX with X10 probes).
Any help will be apprecied.
Thanks!!!

Hello
Dear Sir.
Unfortunately, i have a problem exactly like you. My detection is very very poor, for exp: a nickel coin and silver ring from 1/2 cm!!!
Could you solve the problem?