tektronix 2225 CHANNEL 2 not working properly!!!

[vnashville]

Hi Everybody,

This is my first time in a electronic community forum and my first one posting something so i hope, i will be clear enough  to explain what happened with my 2225:

I just got a Tektronix 2225 from a friend who doesn't need it anymore due to an upgrade and problems on channel 2.

I was able to work and even calibrate channel 1  and works perfect, but every time i try to switch to channel 2 seems like its not working at all, and all i can see on the screen is a fuzzy sine wave that is way out of scale, it goes way out of the entire screen on the scope.

I connected mu siglent sdg1025 to check both channels:

- Only channel 1 response is according to specs and shows all functions from the siglent as expected.
- Channel 2 will keep showing a fuzzy sine wave way out of scale.
- all voltages on power supply working within specs according to service manual and channel 1 working perfect after calibration.

Is the problem on the main board? or the attenuator board?
any possibility of find parts or entire boards for the 2225?
i prefer to replace any of this boards if reasonably affordable but if not necessary i would try to replace the part or parts that doesn't work properly, just got to wait until i have a few weeks after christmas to be able to buy my soldering station and a decent multimeter ( i just started to buying my equipment to implement my little laboratory).

anyway i hope some one can help me. this scope would be a great tool if i got it fixed.

Thanks

[siggi]

Start by getting the service manual. Artek will have a nice scan <http://artekmanuals.com/manuals/tektronix-manuals/>, or there are free copies around.
You may also want to join the TekScopes forum on Yahoo.


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[vnashville]

Hi,

I got the service manual, and tried again to make channel 2 to work but nothing happens. And notice now that i can play with horizontal and vertical controls i still getting that sine wave on channel 2 i can put the function generator on channel 2 but wont show anything the sine wave on channel 2 will be still there no matter if i connect a function generator.

Looking at the manual i've seen the schematics of the vertical attenuator and star checking voltages. (this is the little board on top of the main board near the front right)
i'll keep looking at it but if you have any suggestions i will appreciate to let me know.

thank you.

[MarkL]

Can you provide some photos of what you're seeing working on Ch1 and not working on Ch2?  And wide enough so we can see the front panel settings on the scope.

EDIT: Also, since you have one working channel and one not, you can compare voltages and signals between the two channels point-by-point until you find where they start to be different.  In your case, starting at the attenuator output would be good.

[vnashville]

Hi,

Sorry i couldn't send pictures before but my job kept me real busy.
Well here are the pictures:

first one with both channnels and no signal either comming from my Siglent FG or the probe adjust signal from the scope both look fine:

[vnashville]

Channel 1 with 400mV sine wave from my Siglent FG at 1Khz and no signal on channel 2

[vnashville]

Channel 2 with sine wave from FG and no signal on channel 1

[vnashville]

next one is Channel 1 with FG 400mV sine wave and channel 2 with 500mV square wave from probe adjust terminal from the scope

[vnashville]

in the next picture i notice that by shaking the vertical pot for channel 2 the signal stars changing and looks distorted and the more i play and shake and wiggle this channel the more distorted the signal becomes, like this:

[vnashville]

i tried to clean channel 2 by using some deoxit D5 but seems to me like is not working.
i did shake this pot and again showing me the same problem on screen.

I am hoping not have to replace this entire part cuz i am not sure if there is any replacement for this, instead there is a attenuator card i saw last week for 40 something US $.
But not sure, i am hoping you guys can give me some advice and see what would be the best way to proceed.

Any input will be greatly appreciated.

thanks

[MarkL]

Obviously a mechanical problem.

If just twisting the vertical attenuator through its settings can cause this (i.e., not pushing the knob up and down or side to side), I would first try cleaning the contacts in the Ch2 switch, if you can get to them.  The recommended method is to dampen a small piece of paper with isopropyl alcohol and gently pull it though the closed contact.

The service manual does not have any detail on what these switches look like internally.  Use your judgment if I'm saying doesn't appear to apply.

It could also be a bad solder joint.  To try to find it, use a wooden or plastic stick and put a slight amount of pressure on various components and areas of the board around the switch while you're supplying a signal and watching the screen.

[tautech]

next one is Channel 1 with FG 400mV sine wave and channel 2 with 500mV square wave from probe adjust terminal from the scope

I don't see any problem with this. 

What we can't see are your trigger settings.
Why have you got input coupling set to AC on Ch1? Does the sine wave have a DC offset?

[tautech]

Here's a link to the Operators manual"
https://physics.ucsd.edu/students/courses/summer2015/physics2cl/documents/TEK_Manual.pdf

Become familiar with basic use AND especially use of the Trigger functions as this is how you "drive" the scope.

For most work channel input coupling and Trigger coupling will be to DC. Trigger Slope to rising and Trigger Mode to Auto. Trigger Level to mid way and Trigger Source to the channel of interest.

There's a good step by step in the Manual on P 2-5 "Learning the Controls"

[MarkL]

I don't see any problem with this. 
...

That one looks fine, triggering aside.  Take a look at post #8 at the cal output:

https://www.eevblog.com/forum/repair/tektronix-2225-channel-2-not-working-properly!!!/msg820628/#msg820628

[tautech]

I don't see any problem with this. 
...

That one looks fine, triggering aside.  Take a look at post #8 at the cal output:

Thought he might have had ADD turned on but NO with that.
Yes that one is strange but if you look carefully over the images, settings are all over the place. 

Just trying to get the basics correct Mark, then all should become clear. 

[MarkL]

I don't see any problem with this. 
...

That one looks fine, triggering aside.  Take a look at post #8 at the cal output:

Thought he might have had ADD turned on but NO with that.
Yes that one is strange but if you look carefully over the images, settings are all over the place. 

Just trying to get the basics correct Mark, then all should become clear. 

Agreed - just wanted to make sure you didn't miss it!

[tautech]

@ OP vnashville

Have you made any progress with this?