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 Post subject: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 12:30 am 
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Location: Milford, PA
Hi
I just bought a Tek 475 scope really cheap ($30) and it has a few issues that I need advice with. First and foremost, when using the source switch next to the coupling, if in any other position but channel 2 the trace gets wider, like 1/8 “ or more but in channel 2 position it’s fairly sharp. It doesn’t matter if I have 1 channel or 2 enabled, both will get wider on any source but channel 2. I know this scope did take a little fall ( about 2 feet) Could the tube adjustment be off? The other issues are small, dirty adjustment pots I think. Any advise would be greatly appreciated
Thx


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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 1:29 am 
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Posts: 1840
Location: Dayton, Ohio
"Horizontal Display" push "A" (lock TIME BASE Knobs), (get out of "MIX").

Adjust FOCUS and ASTIGMATISM for small round spot, adjust INTENSITY for reasonable level.

Select either CH 1 or 2 only.

What does it look like now?

Charlie


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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 1:44 am 
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Location: Milford, PA
Charlie,
I tried what you recommended but it’s still the same. When I’m any source but channel 2, both channel traces or singularly when displaying just 1 trace, the channels are considerably wider , mind you, channel 1 is a little wider than 2, but both out of spec. When the source is channel 2, both traces sharpen to within normal limits.
Thx

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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 1:49 am 
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Joined: Feb Sun 17, 2008 11:36 pm
Posts: 1840
Location: Dayton, Ohio
Make sure that the "Mag X10" push button is "out".

Charlie


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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 2:04 am 
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Location: Dayton, Ohio
Exercise the trigger SOURCE switch, but leave it NORMAL or LINE. If this trigger source switch has taken a physical shock, you may have to go inside and look for damage or broken connections.

Charlie


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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 2:19 am 
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Location: Milford, PA
Not sure what it means but the verticals mode switch, which is in normal position but can give 100 or 20 MHz bw, effects this problem. When in normal position it’s much wider but in either 100 or 20 MHz bw, the traces are fine
Thx

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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 2:38 am 
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Location: Dayton, Ohio
I first thought you were talking about the VERTICAL MODE switch as it has Ch 1 and Ch 2 mentioned, then I re-read your first post and thought I misunderstood that you were talking about the trigger SOURCE switch, which has Ch 1 and ch 2 mentioned.

However, the BANDWIDTH switch and several others consist of a "leaf spring" with a small shorting section fastened to the leaf with a bit of plastic.

These are somewhat delicate, the "fingers" must contact both pads when activated. cleaning with a slip of paper, moistened with alcohol (with switch closed), sliding the paper to "burnish" the pad and "finger".

You might want to activate the "BEAM FINDER" switch, to see what effect it has or is working properly.

I would look for broken connections around the BANDWIDTH switch and VERT MODE area.

Charlie


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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Wed 22, 2021 4:31 am 
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Greetings to Bruce and the Forum:

The bandwidth push-button has been installed upside down... for whatever that's worth. There is no "normal" position for this switch. When in the center position, the scope bandwidth is 100 MHz. When pulled out, the scope bandwidth is 20 MHz. When pushed in, the scope is in "trigger view" mode which displays the triggering signal.... which I believe is at the lower bandwidth.

A thickening of the trace represents noise that is being coupled into the vertical amplifier circuits from the trigger pick-off circuitry. You will likely need a second scope to find this problem. You might try placing the mode switch in the "trigger view" position and observing the traces under that condition. With "line" selected as the trigger source and the mode switch in "trigger view", it would also be interesting to see if the displayed sine wave is fuzzy in the same way.

Regards,

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 Post subject: Re: Tektronix 475 scope issues
PostPosted: Sep Thu 23, 2021 2:56 am 
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Well, what they all said but also try just exercising every switch, button, control a few dozen times. The dropping is concerning, but not usually fatal. I have a 465 that took a long tumble, dislodged a few of the boards. I got it working except for the higher sweep speeds, then had to put it aside.

When you get this noise, do you have the input selector switches (AC/DC/GND) in the GND position? If so then it sure sounds like what the last post said.... noise is getting in from "somewhere" ...

I assume that when you get a sharp trace, it stays sharp when you run the intensity all the way up?

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