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Need Guru to look at 5534 scope shot,something is wrong.

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  • #61
    Originally posted by bklein View Post
    Whether or not the IC's are "military" or not is irrelevant.
    In fact, these days what the heck does "military" mean? Made in China or not made in China?
    Actually, military means extended temperature range, and it is required in case you are selling your equipment to, say, NATO. Otherwise, LM2902 is very same as very well known LM324, and that was the point - it draws very little current.

    Just by looking at the components choice, and bipolar pulsing, you could say that primary role for this rig is demining.

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    • #62
      Originally posted by bklein View Post
      Post 13 shows the complete schematic. U2 SI7657? is a negative voltage converter by the looks of it. But can't find anything on that part so I must have the part number wrong. What do you have for V- here? I'm assuming it is the source for the comparator circuits.

      I didn't really get an answer: Should the output if the 5534 be rail to rail? Post #15 shows alternating + and - preamp outputs that I imagine must be symmetrically sampled about the zero V reference point. Problem is that the amplitudes differ significantly. You've got a -1.5 division max. signal vs a +3 division one. I would think they should be the same peak amplitude if they are being sampled equivalently about the zero reference point.

      Looks like I messed up about dynamic damping - instead these are the TX circuits.
      So I go back to whether or not the positive and negative amplitudes out of the preamp should be identical - if yes, are these parts ok?

      Lastly, as for the power draw - it will be the TX that draws the most. Is it enough to skew the negative rail? Whether or not the IC's are "military" or not is irrelevant.
      In fact, these days what the heck does "military" mean? Made in China or not made in China?
      Ok well have another look at post 37 and you can see the output of the 7661 is -4.7 volts,it is a voltage inverter yes.Then post 38 shows the math I have applied to the control circuitry of the regulators. 3.3 volts VC and -2.8volts VE. And that is why you see non symetrical preamp outputs yes,yes they are sampled near the 0v mark,one sample from the positive half cycle,and one from the negative half cycle are fed to the integrator.Look at the regs in the schematic and you will see the voltages are the correct levels,look into the mind of the designer to find out why they are different levels.I dont know.I am going to socket some of the key resistors and do some experimenting,I have to hit the ebay and do some shopping.I did dig up a 5 gallon bucket full of iron with this thing yesterday,when I get that additional transition out of the preamp output this thing will be an animal.

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      • #63
        Originally posted by Brian Deese View Post
        I was having a look at an old pi machine I have that doesnt work very good,using my new scope I saw what looks like ringing on the preamp output.This machine has 330 ohm damping resistor so I didnt think it was ringing.I check the coil signal before the limiting diodes and it looks good,no ringing.I check at the peamp input and it looks good smooth tx pulse,flyback,and tailout to zero volts.But the output of the preamp shows tx pulse,flyback,cross zero opposite polarity,then tailout to zero.Let me post a picture for you.The yellow is the input,the red is the output,second pic yellow is coil signal before diodes,no ringing.
        But what about the cables that connects the coils to the device ? Are the cables original or replaced ? If somebody replace the cable , and new cable does have bigger capacitance - it may cause underdamping of the coil , providing some "overshoot" of the pulse ...

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        • #64
          Brian,
          I think you should come to the condusion the unit is behaving as designed. You want different behavior for different purpose. So decide whether to sell it or modify it.
          If it were me, I would first disable the TX and modify the RX to be symmetrical and rail to rail. The +/- can be reduced from V+/- but symmetrical. Re-enable the TX and see that things stay that way - if not, something there is unsymmetrically drawing power. Given that's good, adjust your sample timing shorter if you can. In fact, if the timing looks right as it is, I would think that is a good indication that the secondary pulse in the preamp output you are worried about is inherent to the design and understood (timing is skewed out alread to compensate). Compare the flyback timing with the Surf PI response and you can get an idea of whether the coil and/or its cable has too high capacitance. Heck, just substitute a quickly home-made or alternate coil. That all good, even the downstream circuits may not be good for your purpose - designed for slower coil movement(?). I guess you had some mention of this in an earlier thread.

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          • #65
            Well I have been away working forever,I wandered into the local army surplus store down here in Wilmington. There was a vintage AF-108 laying there,and it was cheap. So I bought it,thinking I will compare the two machines and see if they are the same.However the new machine is faulty,Q2 the voltage reg transistor gets so hot you cant touch it in about 60 seconds,no output,no lights.I will have to get it home and check it,hopefully Q2 which is a buy92 is just shorted. How do pnp transistors usually fail? do they short or go open? Damn

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            • #66
              I fixed the broken unit about two weeks ago,the overvoltage protection diode on the vc supply was shorted.I removed it and it works just fine,just like the other one. I looked at it on the scope and it is the same in all respects. So it was "as designed" operstion after all. So I have been learning,and collecting information on this great forum for some time now. I decided since I have two of these that I will mod it/them. So for the last two weeks I have been at it with the soldering iron. I have had some good luck with it,and I'm very pleased with it. I got my head wrapped around a couple of circuits that I didn't understand previously. I am uploading a video to youtube right now,I'll post the link when its finished. I will also post the mods that I did to it,and the gains/losses from those mods.

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              • #67
                Here is a video I made this afternoon,inside my house. https://www.youtube.com/watch?v=w_35...ature=youtu.be

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