Threshold Pot doesn't work

[surfdetector]

Thanks dear Carl and green.
My problem is solved. Unfortunately, my two 7660 has problem and can't generate +5V, so my HH1 worked unstable.
Now, my HH1 works very very nice and stable, tp4 is 0, pins 2,3 of IC8 is 0, TP5 and TP9 is 0. I checked the points with my voltmeter and mini O-scope.

The 7805 regulator is what is supposed to be producing the +5 volts. The 7660 is set up as a voltage doubler and feeds the 7805.

[h9361]

The 7805 regulator is what is supposed to be producing the +5 volts. The 7660 is set up as a voltage doubler and feeds the 7805.

Yes, anyway my problem is because of the 7660.

[h9361]

Hello
Dear Carl
I have a question about adjusting TP4 to zero.
I set the point exactly to zero, but the adjusting will be changed after a short time.
For example, i adjusted it to zero yesterday, but it's 640mV now and my HH1 is again unstable!
I again checked my +/-5 voltage, it's OK. Do you think it's because of my bad 5534?!

[Carl-NC]

An offset at TP4 should not cause instability. If you readjust TP4 to zero does it become stable?

[h9361]

No, it is still instability.
I even touch or near my finger to internal coil wire that is connected to 5-pin, my HH1 detects it.
I checked TP5 voltage, my pulse width and main delay pot change its voltage!
As soon as connecting coil to my HH1, i have action even with the slightest movement, even in air.
I also used GPX-5000 coil because it has shield, i again have a very very noisy action!
I think my HH1 is not working correctly, i also checked TP4 form in O-scope, it's OK and can detect metals but it's very very instability.
Do you think my C27, C14 and C15 has problem?

[Carl-NC]

The voltage at TP5 can change if timing is changed. No, I doubt the problem is with those caps. If you see a lot of noise on TP4 then you are probably picking up a lot of EMI noise. Try disconnecting the coil and see if TP4 is still noisy.

[h9361]

If no connect coil, i have no noise in TP4 and my audio is clear.
If no connect coil, voltage of my TP4 is 640mV.
AT is active, i have no noise if coil is static.
As soon as the slightest movement, i have reaction.
Before i tested it in this place more and more, it was very very stable.

[Carl-NC]

If you disconnect the coil and everything is stable then you are picking up EMI noise.

[h9361]

Now i tested it out of my city, it's again unstable with coil, even with commander coil of GPX.
I tested my HH1 more in my place, it was very very stable.

[h9361]

I also tested with the closed sensitivity pot, i still have noise so that i have reaction with the slightest movement.
As you know, i'm using Rev. C2 and the Q5, Q6, Q10, R41, R49 and R51 is not installed.
Only MickstV's audio is connected to pin1 of IC8 (TP5). I even disconnected the audio and connected my voltmeter to TP4, then connected coil to HH1.
As soon as the slightest movement, voltage of the point is increased, it's really very strange.
All of my internal wire is shield type, i checked all of tune points and it's ok.

[Qiaozhi]

I experienced this once when I accidentally connected the TX line of the detector to the shield of the coil cable, and the core to 0V.
Also, note 0V is battery positive on the Hammerhead.
It's either that or your coil cable is microphonic.

[Carl-NC]

He gets the same noise when using a Minelab coil.

Besides EMI, it could be that the gain is way too high. Double check your resistor values. Make sure they are connected properly, with good solder joints. Post a pic of the board.

[h9361]

I experienced this once when I accidentally connected the TX line of the detector to the shield of the coil cable, and the core to 0V.
Also, note 0V is battery positive on the Hammerhead.
It's either that or your coil cable is microphonic.

Yes, i'm using microphonic cable. Now, i changed the shield of the coil cable and core pins, i have still high noise.

[h9361]

He gets the same noise when using a Minelab coil.

Besides EMI, it could be that the gain is way too high. Double check your resistor values. Make sure they are connected properly, with good solder joints. Post a pic of the board.

I think i have to build a new PCB, but this time Rev. D version.

[green]

Thinking disabling Tx might be a good place to start trouble shooting. EMI and EF only. (schematic)https://www.geotech1.com/pages/metde...rhead/HHd1.pdf Could connect Q3 gate to -VB. Where does the jumper go to enable Tx?