Author Topic: Tektronix 2235 issue  (Read 440 times)

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Offline belzrebuth

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Tektronix 2235 issue
« on: September 26, 2019, 01:35:37 pm »
Hi,
I was trying to troubleshoot a function gen (3312A) and after a while I realised that it was actually my scope that had the problem not the generator.
The issue is that square waves of about 10kHz and on are showing like in the attached picture.(10kHz square and 100kHz square generated by a rigol dg1022z)
The problem affects both channels so it should be probably before the input section.
Although it's now showing at the pictures I'm using standard 50ohm bnc cables so it's not a probe problem.
The scope used to work fine because I specifically remember viewing waveforms in the upper kHz range with no problems but as I mostly work with audio this problem can be easily over six months old without me noticing.
« Last Edit: September 26, 2019, 01:40:23 pm by belzrebuth »
 

Offline mzacharias

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Re: Tektronix 2235 issue
« Reply #1 on: September 26, 2019, 04:26:33 pm »
"Thou Shalt Check Power Supplies"
 

Offline belzrebuth

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Re: Tektronix 2235 issue
« Reply #2 on: September 26, 2019, 05:24:01 pm »
DC Voltages are within spec. (5.2V is a little low at 5.08 but still within spec)
Tested as per the service manual instructs on pg 5-4.
Seems like CH2 is different than CH1.
Here's what a 20kHz square looks like on CH1 vs CH2.


edit: Should I mess with the attenuator compensation capacitors for each channel?
The scope seems in a good working order overall so I don't want to mess with its calibration setting unless absolutely necessary.
I mean I could maybe make the problem go away if I tinker with the adjustment capacitors but if there's an actual fault there I may need to calibrate it all over again..
« Last Edit: September 26, 2019, 07:26:37 pm by belzrebuth »
 

Offline rf+tech

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Re: Tektronix 2235 issue
« Reply #3 on: September 27, 2019, 02:49:09 am »
Yes, this is a "probe problem."

A 50Ω cable, attached to a 50Ω signal generator output, must be terminated with 50Ω at the scope end.

Basic transmission line theory.

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Offline belzrebuth

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Re: Tektronix 2235 issue
« Reply #4 on: September 27, 2019, 09:19:00 am »
This is not the issue here I'm afraid.
The problem persists even If I terminate the bnc.
I will go through the adjustment procedure up I think.
Something I've noticed is that when I'm in the mV range the squares look infinitely better than when I'm in the volt range.
The calibration steps for the square wave are also in the mV range..
But my problem manifests in the volt range.
 

Offline 2N3055

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Re: Tektronix 2235 issue
« Reply #5 on: September 27, 2019, 09:31:04 am »
You need to put additional 50ohm terminator resistor on scope side when using BNC cable. Your scope is 1 MOhm input..
 

Offline shakalnokturn

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Re: Tektronix 2235 issue
« Reply #6 on: September 27, 2019, 11:48:39 am »
After replying to the other post, I started thinking: If both channels were wrong in the same way, any chance it is the vertical amplifier frequency response that needed readjusting rather than input amplifiers?
I haven't looked at the S.M.
 


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