2465 CH2 vertical attenuation


Ko
 

I just got a 2465 and almost everything seems to be working. I plan on
doing a full recap, since I want to keep using this scope for a while.

The only issue I found so far is a rather strange one: The attenuation
seems to be occasionally off on CH2.
I sent a squarewave into CH2, 1ms period, 500mVpp. Sometimes the
amplitude is displayed wrong after changing attenuation e.g at 200mV/div
the amplitude looks exactly like at 1V/div (effectively making the
amplitude appear 5x the actual value).
I have also noticed that sometimes the amplitude is displaying as 1/2 of
the actual signal. All these hiccups happen when turning the Volts/Div
knob. I doubt the knob itself is defective since the V/div overlay is
showing the correct value.

channel 1, 3 and 4 work great and have no issue.

Any ideas what could be the issue?


Thank you


Jean-Paul
 

The attenuators can be overloaded and are on tiny gold pin sockets

Get service manual for your série and see the Ch 2 input attenuators

be very cautious in cleaning switches or attenuator contacts, many precautions


Jon


Ko
 

Thanks Jon!
Since a working attenuator on ebay is only around $40-$50 would you agree it's worth just taking a shot at it and replacing ch2 attenuator? Don't want to spend too much time troubleshooting and don't mind replacing it if that likely fixes the issue I'm seeing on my scope.


Siggi
 

The attenuators can get glitchy with age. You should be able to clean them, they're quite serviceable.
See this photo album for some pictures of the attenuators from my 2430: https://groups.io/g/TekScopes/album?id=12814.


Siggi
 

Here's the thread where I discuss the repair of my 2430:
https://groups.io/g/TekScopes/message/106870. It talks about disassembling
the attenuators and de-fouling them.

On Tue, Sep 7, 2021 at 12:33 PM Siggi via groups.io <siggi=
kannski.is@groups.io> wrote:

The attenuators can get glitchy with age. You should be able to clean
them, they're quite serviceable.
See this photo album for some pictures of the attenuators from my 2430:
https://groups.io/g/TekScopes/album?id=12814.






Jean-Paul
 

Ko, a used attenuator is not guaranteed to work, and the root causes could be outside of the attenuators.

For example a contact.

Finally it may be fixable, I would explore further before ordering a spare.

If you at least try to fix it, you may suceed and you will learn how to do it

Jon


Ko
 

Thank you! I found a brand new attenuator, which I ordered.
However, I'll still attempt to take the current one apart and clean it thoroughly.
They service manual is very comprehensive so it shouldn't be too difficult.


Siggi
 

Hey Ko,

Your scope is likely due a calibration anyway, but doubly so if you change
the attenuator. The 2465s maintain per-channel, per-attenuation stage gain
settings for the variable gain preamps, that are set at calibration time.
If you're not planning to calibrate the scope, you may want to at least
check the vertical deflection before and after the swap.

Siggi

Þann mið., 8. sep. 2021, 17:52 Ko skrifaði <k@smo.la>:

Thank you! I found a brand new attenuator, which I ordered.
However, I'll still attempt to take the current one apart and clean it
thoroughly.
They service manual is very comprehensive so it shouldn't be too
difficult.






Jean-Paul
 

Ko, 2465 are circa 1989..1995 (?) and as Siggi mentioned you need a CAL after attenuator work.

There may be effects on transient response as well.

After the repair, performance check at least on Vert Cal and then plan to do a CAL.

The manual has required test equipment and procedures, some substitutes are OK.

Again you will have a great learning experience and our group will be glad to assist your first CAL attempt.

Bon courage


Jon


Ko
 

Thanks y'all for the great input. I took the attenuater apart and cleaned it with IPA followed by deoxit. After putting everything back together, CH2 is working great. I tested different settings on CH2 and amplitude is shown correctly.
Should I still try to get a calibration done even though I'm still using the original attenuator?


Siggi
 

On Thu, Sep 9, 2021 at 1:19 AM Ko <k@smo.la> wrote:

I took the attenuater apart and cleaned it with IPA followed by deoxit.
After putting everything back together, CH2 is working great.

Awesome, congrats on the fix!


I tested different settings on CH2 and amplitude is shown correctly.
Should I still try to get a calibration done even though I'm still using
the original attenuator?
That depends on the state of the calibration of the scope and what your
needs or feelings are.
Note that you can do a reasonable verification of the timebase accuracy of
the scope with the calibrator. The calibrator on these scopes derives from
a crystal-derived clock, and will output 5 cycles across the CRT for most
sweep speed settings.
You can also do a very reasonable verification of the vertical deflection
using a function generator or even a DC power source and a DMM.

Good luck, and enjoy your 2465 - they're awesome scopes.