Surf pi pro very weak sound problem

[Harp]

Trying to make the original "surf pi pro" device, with own PCB design.
Still was missing SMD 7660 chip, which I replaced with 7660 THT connected by wires to board.
I turned on the test, and at the beginning can hear beep, whatever you do next is silence (trimmers, pots).

The only changes I made from the original are minor:
Delay pot 22k instead of 10k + 5K1
PUSH SWITCH below resistors
Exercised the fourth gate from 4066 (for further development when it works).
I enclose the scheme, which is precisely the current situation on the board.

I measured voltage:
battery source: 11.92V
+ VBATT (board): 11.81V
7805: 4.92V
7660 Pin5: -4.13V (strangely low?)
5534 pin6 set to 0.00V

555 / IRF is working fine, very slightly heated.
4066 pin8 (see scheme below) coupled with base MPSA13 gives weak sound..
PUSH SWITCH gives a strong sound.

With a very large iron object 10cm away from the coil hear a weak sound from the headphones, but not reacted to the 10k threshold. By turning the potentiometer 100k gain it immediately loses.

I suspect the coil, and these days I'll try to do better. But I do not know if it can be so strongly affect the operation of the unit.
0.7mm, ID22cm, 25 turn, flat spiral around 300uH.

If the unit is correct, whether it be turning 10k threshold at some point you reach a point from which still can hear sound of the oscillator? For me it does not hear, and that worries me.
I read all about spp problems on this forum from Q, but there was no help.
Please advice, I only have a multimeter, beautiful device that does not work and a lot of will.
thank you!

[Harp]

I made a test with the speakers connected to GND.
The coil was attached, but I have not tested with metal.

Anomalies that I noticed I'd ask the experts here:

Negative -5V gives a very weak dull sound.
4093 pin10 delivers crystal clear, strong sound, but 4066 pin8 not make any sound
Tips are welcome!

[Harp]

I replaced the 555, 4093, 4066 and 7660.
Now I have a negative voltage -4.34V, I checked C8 and C9 (220uF).
I made a new coil of 300uH and 0.8 ohms.

I replaced R2 (3K3) with the a 10k potentiometer.
I replaced R6 (damping) with the 1k potentiometer.

And as a result, I can not never rid of voltage 3.72V at 358 pin 1!
What else should test, tune or replace? I'm already in despair ...

[württemberger]

Change from the Tresholdpot Pin 1 and Pin 2.
The Center Tresh. Pin 2 must go to R25!

[Harp]

Was already thinking that I answer that this is not a mistake, that I was intentional put the central pin to side (which actually I did), but prompted by your observations, I took a multimeter and measure the reality ...

Thank you, it was definitely a mistake!

I had a pot of one unit who already had connected connector. I thought to use it so I just solder the pins on the circuit board. I even went specifically 'to correct' the PCB to put the 'pin2' on the side ...

Since I had not worked with multiturn potentiometers, I overlooked that the mark on the case is not 123, but 213, and from there mistake.

I noticed that the wire replaced on the connector, however, since the pot is of a specialized unit, I thought they intentionally put 'pin2' on the side.

-----------------------------------------
This change has brought me a function of the potentiometer, but I still can not get a good (useable) operation of the device.

I made a new one, one more coil, 230uF, 1.3 ohms, flat spiral. With it I was able to get the 'signs of life', but only if R2 is set to a very small resistance around 400 ohms! From there I guess the result that there is no power for a longer detection, the the IRF have complete cold!

If I increase the R2, even for very little, just get 3.7V at 358 pin1, and the device stops working.
How could I keep R2 = 3K3 like the original, and that 358 pin1 not go too high?

Thanks again!

[Harp]

I replaced the resistors 358 amplifier: 475K / 220n with 220K / 470n (such the surf pi works)
The problem has remained the same - the output of 358 is 3.7V
Here are a few pictures if someone can see the error, it would be helpful.
556 circuit and associated components in the middle of the board is not connected to anything.

[Harp]

Did any of you manage to make surf_pi_pro by the original scheme without any modification (except damping/coil)? How to solve the problem of overloading 358?

[zelkos]

O yes, I did, without any problems.
Scheme for which I worked, was in the original thread "SurfXX", PCB was "cosmetic" changed to elements that I used.
After everything was done, I started to change certain elements in order to obtain better performance.

[Harp]

Thank you!
It is obvious to me a bigger problem, because whatever I replace it remains overloaded. Maybe arrangement / design is not good ...