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577D1 Phantom base current


DW
 

I have a 577 that has developed a interesting problem

It seems to be exclusive with transistors when the base terminal is used, when I am testing components such as diodes where only the base and collector are used there is no issue.

I included pictures that describe the problem or you can check the Tekscopes photos and look for 577 Phantom Base Current. Notice the first picture how there is a vertical positive offset on the IV curve, this doesn't appear to be normal. Notice the second picture where the step generator is set to single but some form of current exists. If I pull the transistor the phantom current disappears, if I install another transistor the same phantom current appears once more. If I adjust the step amplitude then I notice a proportional effect on the phantom current, increasing amplitude increases the magnitude of the phantom current. I have the offset controls disabled. Any thoughts on this, thanks

https://groups.io/g/TekScopes/photo/255355/0?p=Created,,,20,2,0,0


DW
 

Here is a idea

If someone with a 577 curve tracer try this test, install a transitor and with the step generator set to single and increase the collector voltage does the display indicate some current. Does moving the step generator amplitude proportionally effect the amount of current displayed?

I am thinking if someone could duplicate this with a good known 577 we will see if this is by design or if it is a fault.

Thanks


Michael W. Lynch <mlynch003@...>
 

On Mon, Oct 19, 2020 at 01:30 PM, DW wrote:


Here is a idea

If someone with a 577 curve tracer try this test, install a transitor and with
the step generator set to single and increase the collector voltage does the
display indicate some current. Does moving the step generator amplitude
proportionally effect the amount of current displayed?

I am thinking if someone could duplicate this with a good known 577 we will
see if this is by design or if it is a fault.
DW,

I tried this with my 577 and with a PNP transistor in the standard test fixture. I have inverted the display so that the traces appear first at the bottom left of the CRT. With the # steps Control set to 1 step, I increase the collector voltage and I see the first line of the trace advance across the bottom at Zero (bottom graticule line), a single step appears above the ZERO Line, at whatever the step current control is set to. So I do not have any current offset indicating on the ZERO line. The ZERO Line remains at ZERO, indicating voltage being present with no current flow. Is that what you are looking for?

--
Michael Lynch
Dardanelle, AR


DW
 

Michael,

Thanks for the reply. From what you observed I am not getting the same results. The phenomenon I am experiencing seems to be an issue with improper biasing on the base terminal.

When you set the set the step generator to the single setting, do you notice when raising the collector voltage there appears to be current increase initially then levels off horizontally across the display. And when setting the step amplitude higher or lower this will affect how how much vertical deflection until the line goes horizontal again. Or does it just stay flat at 0. I hope this makes sense.


Michael W. Lynch <mlynch003@...>
 

DW,

My "ZERO Line trace" stays flat, right against the bottom of the CRT graticule. When testing a transistor with the steps set to 1, I see two lines, the first is that "zero line trace" at the very bottom of the CRT and when increasing the collector voltage this line always moves straight across from left to right, with no perceptible vertical deflection. The next line or trace would be the single trace that you would expect to get. As the collector voltage knob is increased, that trace moves left and up from the corner of the graticule, as one would expect. Of course, this is indicating increased voltage as well as the presence of current. The ZERO line is always present , representing the collector voltage knob position, regardless of the number of steps selected, except when the collector voltage knob is set to zero; when it becomes a single dot. Hope this answers your question.

--
Michael Lynch
Dardanelle, AR


Jack2015
 

DW,

The offset is adjustable by the Offset Multi knob(the big metal knob) when "AID" button is on and "Zero" button is off,
when the "AID" button is off and "zero" button is off you can turn the knob to adjust the number of steps.
Did you try to turn the "AID" button off?


Michael W. Lynch <mlynch003@...>
 

On Fri, Oct 23, 2020 at 06:26 AM, Jack2015 wrote:


when the "AID" button is off and "zero" button is off you can turn the knob to
adjust the number of steps.
The Aid and Offset buttons are independent of the Steps Knob. You may select any number of steps (1 to 9), regardless of how the Offset controls are selected or adjusted. Even with the offset control "On" and in the "Aid" position, with the offset control at "Zero", your baseline trace should and must remain at the bottom or top "zero" line. If you adjust the Offset Control vernier above Zero, then the base trace along with all subsequent traces will move up or down, depending on whether the "oppose" or "aid" button is depressed. At least, this is my understanding and how my 577 and both 576 curve Tracers operate.

--
Michael Lynch
Dardanelle, AR


Jack2015
 

Yes,You are right!

I suspected the "Aid" button because the photos DW provided have shown the traces moved above zero line with the "Aid" button depressed,
hope it's just an operation issue.

https://groups.io/g/TekScopes/photo/255563/1?p=Created,,,100,2,0,0
https://groups.io/g/TekScopes/photo/255563/0?p=Created,,,100,2,0,0