Author Topic: Tek 475 fade in from left at 0.2,0.1,0.05us time/div  (Read 2016 times)

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Offline rz

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Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« on: May 26, 2017, 08:48:26 am »
      I bought a tek 475 scope. All works fine except the trace fade in from the left about 1-2 grids when the time/div is at 0.2, 0.1, 0.05us. I have read the troubleshooting manual, but no exact problem in the manual.

      I suspect the problem is in the Z-axis circuits. In the service  manual, Q680 is used to ensure proper early turn-off CRT at faster sweep rates.
 

Online Andy Watson

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #1 on: May 26, 2017, 09:03:37 am »
Mine does that. I think it is normal.
 

Offline tggzzz

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #2 on: May 26, 2017, 10:06:24 am »
There is a tweak in the service manual.

What you need to be able to see is >10 divisions of visible sweep, plus, for a square wave signal used as a trigger, the leading/triggering edge of the square wave.

If you can see both those, there's nothing to be concerned about.
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Offline rz

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #3 on: May 26, 2017, 10:41:13 am »
Mine does that. I think it is normal.

Thank you for the reply. Hope it is normal. :)
 

Offline rz

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #4 on: May 26, 2017, 10:42:25 am »
There is a tweak in the service manual.

What you need to be able to see is >10 divisions of visible sweep, plus, for a square wave signal used as a trigger, the leading/triggering edge of the square wave.

If you can see both those, there's nothing to be concerned about.

The trace are fade in. If the time/div > 0.1us, the trace can start from the left edge of the CRT.
 

Offline coromonadalix

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #5 on: May 26, 2017, 11:14:26 am »
Maybe stupid question,  does your position pots works ?  If you use the beam finder, are you able to put the dot / line in the screen center ??
 

Offline rz

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #6 on: May 26, 2017, 11:19:25 am »
Maybe stupid question,  does your position pots works ?  If you use the beam finder, are you able to put the dot / line in the screen center ??

Thank you. I can see the whole trace by adjust the position pot. I just wonder is this a malfunction of the scope.
 

Online T3sl4co1l

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #7 on: May 26, 2017, 12:27:20 pm »
Mine does that, too.  I think there's something wrong with the Z axis, but I never looked into it.

It is a problem, because fully the left half of the trace is invisible at maximum sweep.  Trace intensity has to be turned up all the way so that retrace is visible (i.e., defeating blanking altogether -- probably not healthy), to see it.

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Offline tombi

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #8 on: May 26, 2017, 01:37:52 pm »
Ha!

I spent a good long while debugging this problem on mine before I discovered it was normal.

One thing you can do is to run through the Display and Z Axis Calibration procedure (3-10 in my manual) and in particular the Grid Bias and Z Axis compensation. This should help to  brighten the trace on the left side.

Just make sure its warm before you begin. Oh and be careful about what you touch!

Tom
 

Offline whitevamp

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Re: Tek 475 fade in from left at 0.2,0.1,0.05us time/div
« Reply #9 on: May 26, 2017, 02:13:07 pm »
mine is visable with the position knob at half way " center position. " and dose not change till i hit about 3/4 of the way to left or right.
 


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