Originally posted by ivconic
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Need Guru to look at 5534 scope shot,something is wrong.
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Originally posted by Davor View PostAh, so you actually measure the opamp feedback compensated input, and not the voltage on the coil. OK, that makes sense. Trouble with such measurement is that you actually look at the place where a voltage should be different from zero only in times the opamp is saturated, and such measurements will lead you nowhere. This is very different from non-inverting opamp stages where input follows the applied voltage. The inverting one fights back and tries hard to keep its input at zero. What you observe is just the way the opamp recovers after saturation, and it is perfectly OK the way you see it.
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Originally posted by ivconic View PostThat's why i suspected diodes and base "biasing" voltage. It is "fast" PI machine yet with bipolar transistor and not with fet. It is much more difficult to control bipolar transistor in such conditions, so any possible variations at base voltage would cause also something like "ringing" and indirectly will affect rx too.
I had similar issues long time ago with such "bipolar" design.
You actually don't need to resolder diodes to examine them; just measure voltage across them. (that's why i gave you reference 6.75V to start with)
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Hi Brian,
Do you have an original or home made coil on the machine?? Looks like it is under damped, but you already have a lower value damping resistor than original so decreasing the value of the damping resistor should correct the trace, but it will make it take longer for the coil to settle and will also degrade performance. I think you have a capacitance problem with the coil, the C is too high.
Also some diodes in the feedback loop of the opamp would not go astray to prevent the opamp from going into saturation. This should speed up the opamp settling time.
I do find it odd that the supplies are not matched for + and - too, perhaps Carl could shed some light on this.
Cheers Mick
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Originally posted by Mechanic View PostHi Brian,
Do you have an original or home made coil on the machine?? Looks like it is under damped, but you already have a lower value damping resistor than original so decreasing the value of the damping resistor should correct the trace, but it will make it take longer for the coil to settle and will also degrade performance. I think you have a capacitance problem with the coil, the C is too high.
Also some diodes in the feedback loop of the opamp would not go astray to prevent the opamp from going into saturation. This should speed up the opamp settling time.
I do find it odd that the supplies are not matched for + and - too, perhaps Carl could shed some light on this.
Cheers Mick
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HI Brian,
After the solder bridge was removed was there any change in the - supply voltage? If anything were damaged it would most likely be Q3. If you apply some extra load to the supply does it compensate to keep the correct/same voltage? If the supply voltage is low this could be causing a problem with the tx transistors not turning off properly perhaps.
If you have the original coil, then it is not likely there will be a problem there.
Cheers Mick
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Originally posted by Mechanic View PostHI Brian,
After the solder bridge was removed was there any change in the - supply voltage? If anything were damaged it would most likely be Q3. If you apply some extra load to the supply does it compensate to keep the correct/same voltage? If the supply voltage is low this could be causing a problem with the tx transistors not turning off properly perhaps.
If you have the original coil, then it is not likely there will be a problem there.
Cheers Mick
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Ok I got to looking at the divider( R7 and R8 ). at the input of U1A.I found an resister divider calculator to do the math.So U1A is going to be output high until the non inverting input matches the inverting input 0V,so we consider that pin to be zero volts if the regulator is working,then we say VC is 3.48V then do the math of the resistor divider and we get VE = 2.9V which is roughly what I have at 2.82V. So before I put my foot in my mouth I applied the same math to the positive regulator,D4 a 1.2v reference diode,connected to the non inverting input of U1B,and another divider to the inverting input.assume once again the center of this divider is 1.2V given that the regulator is working,insert the resistor values in the calculator and you get VC = 3.34V and this calculation is made with no respect to the battery voltage.Only the 1.2v ref diode and the resistor divider values are used. So there was no room for error like the above calculation for the neg,where I had to enter the VC value. So isnt 3.3V a pretty standard control voltage? I think I am solid now on the voltage supplies.
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Here you can find how old detector http://www.geotech1.com/forums/showthread.php?t=12357
Here scheme with better resolution http://www.geotech1.com/forums/showthread.php?t=18157
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HI Brian,
Have you checked the 1k series resistor on the input path to the preamp to make sure it is 1k. Although this would not be causing the under damping problem anyway as the parallel diodes have stopped conducting by the time the problem shows up. Hmmmph!
Have you checked that the coil ground(0v) is all connected properly and that the damping resistor is connected to it properly?
Have you checked that the coil is wired correctly to the plug?
As far as I can tell the tx transistors seem to be working properly, the power supply seems ok too.
Can you check when the first sample is being taken by the 4016 (pins 5 & 13) compared to the preamp output?
Do you have access to another coil?
Cheers Mick
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Originally posted by Mechanic View PostHI Brian,
Have you checked the 1k series resistor on the input path to the preamp to make sure it is 1k. Although this would not be causing the under damping problem anyway as the parallel diodes have stopped conducting by the time the problem shows up. Hmmmph!
Have you checked that the coil ground(0v) is all connected properly and that the damping resistor is connected to it properly?
Have you checked that the coil is wired correctly to the plug?
As far as I can tell the tx transistors seem to be working properly, the power supply seems ok too.
Can you check when the first sample is being taken by the 4016 (pins 5 & 13) compared to the preamp output?
Do you have access to another coil?
Cheers Mick
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Originally posted by Mechanic View PostHI Brian,
Have you checked the 1k series resistor on the input path to the preamp to make sure it is 1k. Although this would not be causing the under damping problem anyway as the parallel diodes have stopped conducting by the time the problem shows up. Hmmmph!
Have you checked that the coil ground(0v) is all connected properly and that the damping resistor is connected to it properly?
Have you checked that the coil is wired correctly to the plug?
As far as I can tell the tx transistors seem to be working properly, the power supply seems ok too.
Can you check when the first sample is being taken by the 4016 (pins 5 & 13) compared to the preamp output?
Do you have access to another coil?
Cheers Mick
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Hi Brian Deese. You had a detector in working order, but you were not satisfied with the detection of small objects (aluminum cylinder 10mm tall,8mm diameter at 20cm... its too slow to signal...) http://www.geotech1.com/forums/showthread.php?t=17571
What did you do after?
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Originally posted by maikl View PostHi Brian Deese. You had a detector in working order, but you were not satisfied with the detection of small objects (aluminum cylinder 10mm tall,8mm diameter at 20cm... its too slow to signal...) http://www.geotech1.com/forums/showthread.php?t=17571
What did you do after?
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