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.
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Need Guru to look at 5534 scope shot,something is wrong.
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Most likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away.
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Originally posted by Carl-NC View PostMost likely the coil is very slightly underdamped, not enough to see it on the scope but enough to make the preamp flip. Slightly reduce the damping R by adding a resistor in parallel (perhaps 10k) and see if it goes away.
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Originally posted by porkluvr View PostDoes your design call for maybe a 3pf (or more) feedback capacitance across the 5534 i/o, or maybe 3pF (or more) across pins 5~8?
You've thrown us a bone, what about showing us the whole front end?Attached Files
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Is it normal for the positive and negative supplies to be different levels,last night I measured vc at 3.48v and ve at 2.82v if I recall.The other machines I have use 5v+/- supplies.If you change the hor division on the scope to see 3 cycles you can see the difference in the output of the amp.
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Originally posted by Brian Deese View PostIs it normal for the positive and negative supplies to be different levels,last night I measured vc at 3.48v and ve at 2.82v if I recall.The other machines I have use 5v+/- supplies.If you change the hor division on the scope to see 3 cycles you can see the difference in the output of the amp.
It's impossible to determine the timebase and amplitude/division from your photo.
I was going to tell you that your scope shot really looked OK to me considering the high gain; slow recovery would be normal... but then I can't understand why your output would be FOLLOWING the input instead of inverting it and being a mirror image. So maybe I just better shut up instead.
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Yeah what he said...
Looks like you have dynamic damping on the coil.
Is this a homemade implementation or a commercial one? (fixing or making?)
Remove the damping portions (upper/lower) temporarily (lift resistors or diodes). See if you get what you'd expect.
Make sure offset is correct (play with it, or center with no input signal).
Make sure zero V on one side of schematic is connected to the zero V on the other.
+/- voltage seems very low - do you have that schematic? I'd expect higher.
Maybe something elsewhere is loading down your supplies.
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Originally posted by porkluvr View PostThat may be another problem.
It's impossible to determine the timebase and amplitude/division from your photo.
I was going to tell you that your scope shot really looked OK to me considering the high gain; slow recovery would be normal... but then I can't understand why your output would be FOLLOWING the input instead of inverting it and being a mirror image. So maybe I just better shut up instead.
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Originally posted by bklein View PostYeah what he said...
Looks like you have dynamic damping on the coil.
Is this a homemade implementation or a commercial one? (fixing or making?)
Remove the damping portions (upper/lower) temporarily (lift resistors or diodes). See if you get what you'd expect.
Make sure offset is correct (play with it, or center with no input signal).
Make sure zero V on one side of schematic is connected to the zero V on the other.
+/- voltage seems very low - do you have that schematic? I'd expect higher.
Maybe something elsewhere is loading down your supplies.
It is a whites af-108 and I am trying to repair it.
I have centered the offset.
I have played with the offset in the past,I have got more sens with it offset from zero,but I dont remember the value.As of now its set at zero though.
I do have the schematic,I will post it.It uses linear regs made of discreet components.Attached Files
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