help with surf pi kit no sound

[alcartraz]

unfortunately i dont have a scope only a multimeter it can measure frequency and duty cycle inductance and capacitance and the normal stuff

[alcartraz]

just tried another experiment e.m.f meter iam getting a good field from my coil max depth 60cm approximately tried my whites idx about the same from that coil too so iam getting a magnetic field

[alcartraz]

frequency at coil connection coil end is 1.197 KHz
frequency at tp1 0.598 KHz
duty cycle at tp1 87.3 %
volts at tp1 4.75 -
volts at tp2 0 volts
dont mean a lot to me but might to some one ?

[alcartraz]

could it be the coil making it very low in sound ? if touch the coil with bare skin enameled wire and and pin on volume pot turn voulme to mid way the sound comes up to an useable level constant tone still dont react to metal try delay adjustment makes no difference

[Qiaozhi]

With the coil disconnected, what is the voltage at TP2?

[alcartraz]

hi thanks for helping volts at tp2 0volts with or without coil

[Qiaozhi]

hi thanks for helping volts at tp2 0volts with or without coil

Does the voltage at TP2 change when you adjust P1?

[alcartraz]

yes

[Qiaozhi]

So far it looks like the power supplies are working OK, and the correct power voltages appear in all the right places. The null-offset of the preamp can also be adjusted to 0V, and a magnetic field is being transmitted by the coil. However, without an oscilloscope, the cause of the problem is going to be very difficult to find.

I'm a bit concerned that the preamp output (TP2) is still 0V with the coil connected. Does the voltage increase by a few mV if you put a large metal target near the coil?

[alcartraz]

i read setting it up tp2 was to be set at 0v is this right do i set it with the coil off or on the offset is a bit touchy down to the last few mv and all ways changes the next time i test it as for large metal object how large i will try and post results soon thanks for helping again i might be able to gain access to a scope but never used one before

[alcartraz]

ok a little more playing around i found q6 11.97 going in on collector 0 volt on base 0volts on emitter ?

[Qiaozhi]

ok a little more playing around i found q6 11.97 going in on collector 0 volt on base 0volts on emitter ?

That's an interesting observation.

There should be a square wave at the output of U4D that is used to switch U7D (4066) on and off. This means that Q6 base is either at 0V (4066 turned on) or is biased to a higher voltage by U3A (LM356) when a metal target is near the coil (4066 turned off).
I know someone asked this earlier, but are you sure the link above R16 is inserted?

Looking at the original White's circuit diagram for the Surf PI, I notice that it has an audio transformer in the collector of Q6. This implies that the speaker needs to a high-impedance type, if you're not using a transformer.

[alcartraz]

been playing some more the volts on tp2 goes from 0 volts to -1.9 when near to touching a metal object made of steel and yes the two links marked with white lines are there and good

[Qiaozhi]

been playing some more the volts on tp2 goes from 0 volts to -1.9 when near to touching a metal object made of steel and yes the two links marked with white lines are there and good

Can someone check this on a working Surf PI?
Looking at the schematic, I would expect the signal at TP2 to go positive when a metal target is present.

Alcartraz - tell me about your coil. What is the diameter, and how many turns?

[alcartraz]

67mm radius 0.560 enamaled copper wire 22 turns but just checked the calculator it says 31 for 0.3mh is that right the last calculation ?