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  • #1

    Problem with TGSL

    I have made TGSL and it has wierd problem. When coil is connected to TGSL and i switch power on it starts make piiiiiiiiii.....p and continues until switsched off or coil is disconnected, connecting coil back then sound starts again. TGSl does not respond to metal or pots neither. Have cheked for bridges and lose connections, but everything looks like it should be. Cheked components even before soldering for faults, have tried different IC-s but nothing changes. I dont have o-scope for test, i can measure V, Hz, inductive with my tester. TGSL coil is not yet shielded, stiff and glued, wrapped with tape.
    Has someone seen shuch problem before and what might be the solution for this.



    This TGSL version http://www.geotech1.com/forums/showthread.php?t=15710
    Tags: None
  • #2
    Check all your voltages first

    Do you have 12v, 8v and -5v

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    • #3
      From your description, I suspect it's a coil problem.

      What coil are you using? Is it a commercial coil or a homemade one?
      If it's a homemade one, how did you balance the coil without an oscilloscope?

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      • #4
        I have marked measured voltages to picture. Coil is homemade and its not finished, both D-s are movable. I should be possible to balance coil by measuring u101 pin 7 to aim it for 0v. I got some sort of reading material from this forum, for alternative balancing. After messing with my tgsl the sound has changed a bit from constant piip to fast pip-ing. Have changed 7808 to other 7808 because 8v was more like 9v.
        Attached Files

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        • #5
          Originally posted by gazjeep View Post
          I have marked measured voltages to picture. Coil is homemade and its not finished, both D-s are movable. I should be possible to balance coil by measuring u101 pin 7 to aim it for 0v. I got some sort of reading material from this forum, for alternative balancing. After messing with my tgsl the sound has changed a bit from constant piip to fast pip-ing. Have changed 7808 to other 7808 because 8v was more like 9v.
          The TX oscillator seems to be working, otherwise you would not have a negative supply rail. Have you measured the frequency of oscillation?
          I assume the SENS control is turned down?

          First switch to All-Metal mode, and then measure across C12 and C15. In both cases the voltage level should change when you adjust the ground balance pot. If it does, then adjust the voltage to somewhere near zero, and move a metal target near the coil. Does the voltage across C12 change in value?

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          • #6
            C12 has -4,8v to -5,3v when i turn ground pot, c15 has -0,35v all the time, moving a metal object over the coil changes nothing. Same with disc and all-metal mode. On the picture test point 1 value is 14,35hz and test point 4 u101a pin 7 value is 14,37hz. If i turn disc pot both hz will rise to 14,45hz in all-metal and same with disc mode.

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            • #7
              Originally posted by gazjeep View Post
              C12 has -4,8v to -5,3v when i turn ground pot, c15 has -0,35v all the time, moving a metal object over the coil changes nothing. Same with disc and all-metal mode. On the picture test point 1 value is 14,35hz and test point 4 u101a pin 7 value is 14,37hz. If i turn disc pot both hz will rise to 14,45hz in all-metal and same with disc mode.
              The frequency measurement of 14kHz shows that your TX oscillator is working. Of course, the frequency at test point 4 will be exactly the same. It cannot be anything else. This shows that the pre-amp is also working, but without an oscilloscope it is not possible to check if the pre-amp output is saturated. However, the fact that a metal target moved near the coil does not produce a response across C12 indicates one of two things: 1) the coil is not properly balanced, or 2) the GB sample pulse is missing. The most likely cause is the first one, but (again) without a scope this is going to be difficult to debug.

              Here's one possible solution:
              Set the ground balance control to its middle position, and connect your meter across C12. Change the overlap between the coils until this voltage is close to zero. Then try moving a metal target near the coil.

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              • #8
                It will not go over -4,6v, goes down to -5,05v but thats all. Sometimes it just jumps to -2,5v but i cant force it to happen. Those voltages are always moving up and down too, -4,6v to -4,8v. I think this board is bit toasted and perhaps its wiser to make new one. This one is second. First was actually working but i managed to mirrorise the pcb with printig this "press-n-peel" film. So all the IC and other parts were like upside down.

                Comment

                • #9
                  Originally posted by gazjeep View Post
                  It will not go over -4,6v, goes down to -5,05v but thats all. Sometimes it just jumps to -2,5v but i cant force it to happen. Those voltages are always moving up and down too, -4,6v to -4,8v. I think this board is bit toasted and perhaps its wiser to make new one. This one is second. First was actually working but i managed to mirrorise the pcb with printig this "press-n-peel" film. So all the IC and other parts were like upside down.
                  You might just have to admit defeat and buy an oscilloscope.
                  One other thing you could try is to connect your circuit to a commercial Tesoro coil.
                  Or - simply buy a kit from Silverdog ->
                  http://www.silverdog.co.uk/shop/inde...&product_id=99

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