TGSL Tuning & troubleshooting

[BKY1337]

I have bought a DSO150 right now. I hope i can use it to find the problem.

[dbanner]

Well, yes the oscillator should run independently with only coil connected. Remove U101 and U102 from circuit, oh I forgot yours is surface mount. Disconnect one end of C9 and C10 to isolate U101 and U102. This will completely isolate the oscillator. Also check TR6. remove CD4024 also. Then check oscillator again.

[BKY1337]

My Resistances are 25,4 and 24,5 Ohm. The coil is ok. I swapped the cables for TX and RX and i have a null voltage of 0.200V now.
But this was not the problem.

I still have the steady tone and only 3mV at the coil.

I got this problem while i tried to null my new graphite coated coils. It began to chatter and then i saw that the speaker is under the board and i pulled him out and the speaker touched some pins and i have the steady tone since then.

Should the colpitts oscillator work independent from the other things in this circuit? Could it be that a positve voltage neutralizes my negative 16 Volts at the coil from an other part of the circuit?

[dbanner]

That' because your TX coil is shorted. measure resistance of your coil

[BKY1337]

I already used this dmm to measure the tx voltage and it worked. I replaced the 358 with a TL082 and it didnt change anything. I removed the 4024 and the detector became quiet.

I just cant understand why i only have 4mV where i need to have -16Volts. Every part in the colpitts oscillator is working.
I have 8volts supply and i have 5,6V at the base of the transistor , the transistor is working. What voltage do i need to have between the parts?

I have a null voltage of 4 Volts at pin 7, this is maybe because i have connected the coil wrong. Its only a test coil.

I measured the pin 8 voltage of this op - amps because hyena asked in an older post for this.

[dbanner]

Plese dont tell me that i need to buy a oscilloscope. I measured with Multimeter.

[ATTACH]42013[/ATTACH]

Oh no, of course not. I made TGSL without proper scope, I only used multimeter and simple soundcard oscilloscope software.
The reason why I asked is because cheapo meters do not have enough frequency response to measure TX.

[waltr]

Plese dont tell me that i need to buy a oscilloscope. I measured with Multimeter.

[ATTACH]42013[/ATTACH]

Pin 8 of the LM308 op-amps is a COMP pin. This problibly tells you nothing.
Pin 8 of the LM393 & LM358 op-amps is V+. DMV measurement tells you there is power.
Did you Google search and LOOK at the Data sheets for these op-amps????

For any input/output of the analog signals and even the digital switching/clocking an O'scope really is a requirement.

[BKY1337]

Plese dont tell me that i need to buy a oscilloscope. I measured with Multimeter.

[dbanner]

What are you using to measure the voltage?

[BKY1337]

I desoldered and tested the 2n2907 and the two poly caps. everything is working. I have 14,21 khZ but only 0,003V instead of 16 Volts. What can be wrong?.

[BKY1337]

I have a problem again. I short connected my board somewhere with the speaker.
I have a steady loud audio tone. I get this steady tone even without LM358.

I have steady 1,2V at the Base from BC547 and steady 6,4V at the collector of the same transistor.

I saw that i have only 3mV at the tx 1 connector.

I can see that the colpitts oscillator is supplied with 8 Volts. I have 5,6 Volts after the 24k Resistor.

Maybe my 2n2907 is damaged and cause the 3mV. But i dont think that this causes the steady tone.

What do you think? Is there a replacement for the 2n2907?

[homefire]

LOL, And here I was thinking I was the only one who's done that.

[dbanner]

This was my first TGSL build, notice chips are soldered on foil side. This was error forgetting to mirror layout before printing.

[dbanner]

If i remember correctly, when I built my first tgsl, I did not have a scope, so what I did to null coils was to put meter directly across Rx and adjust position for minimum induced voltage(null), then I connected Rx to circuit. Once i got it working, I adjusted it for maximum detection range(moving a variety of coins etc across coil), then I put GB trimmer at mid position and used small ferrite rod while adjusting trimmer until ferrite was not detected. I used a pc based scope which could also measure frequency of waveform, this is how I knew my TX was oscillating at correct freq. so I could calculate that my coil was correct inductance. You can also connect Rx coil to TX oscillator to check inductance of Rx coil. The inductances of coils are critical to proper functioning of circuit.

[BKY1337]

Yes i know!