Products > Test Equipment
Tektronix 2235 AN/USM 488 - Diagnosis Help
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Arts:

--- Quote from: WhatsICC on May 18, 2023, 06:14:39 pm ---Thanks! I heard so much about the Tek Yahoo Group until they did away with groups, ill make good use of that link.

The store is - Electronic Surplus Industries in North York.
I had to drive a little over an hour from where I am, but this store is just filled top to bottom with testing equipment. Barely any room to walk (in a good way haha)... you can spend hours upon hours browsing

I'm excited to own this 2235, I've read mixed reviews about it but if i can get the traces dialed in ill be more than happy. I hope its just my probe compensation ill have to go out and fiddle with it some more but I dont think it is

--- End quote ---

My own 2235 started acting up a while back. It has always been a great little summer-scope ( I use my ancient Tektronix 547 as my combination winter-scope/shop heater) so I decided to give it a proper tune-up; all of the electrolytics, IEC line filter and associated caps, focus resistors, delete MOSFET connector etc. Good as new now :) 

All you need to know is right here: https://w140.com/tekwiki/wiki/2235

That store sounds like a place I'd like to visit, but it would be a bit of a drive from Montreal..
TERRA Operative:
My scope is rock solid and great to use, it had some problem with the focus due to drifted carbon composite resistors (a common but easily resolved issue) but after the upgrades in my video linked above, it's working great.

It sits just at a nice point between simplicity of use and good specifications for day to day use.



Re. Arkek, the owner recently passed on so his wife and other staff are picking up the pieces, so while they are still operating AFAIK, be understanding if there are delays on delivering the manuals.
WhatsICC:

--- Quote from: David Hess on May 18, 2023, 06:24:44 pm ---The screen over the CRT is for electromagnetic shielding and was an option on many Tektronix models.  I think if you remove the CRT bezel, then the screen can be easily removed.

My guess is that the power supply voltages, including the acceleration voltages, are sagging under load.  When the beam is at either vertical extreme, one side of the differential output stage draws more current through the load resistors.

If this is the case, then it should show up with a voltmeter measurement as the beam position is changed and the intensity is adjusted.  The service manual gives details about checking the power supply voltages.

Before getting too involved, run the same tests on the 2nd channel, and with DC coupling selected instead of AC coupling.


--- End quote ---

Much better with DC coupling, I swore I had tried it in DC the night before and it was acting up even setting my ground point to zero then back to dc the 1khz signal was falling well below 0.

However, tried again last night both channels working great in DC! However some funny business going on in the Horizontal Mode and in AC... I'll have to fiddle with it some more, I'm waiting on my signal generator.

I think for now I'm gonna replace the Rifas at the minimum and do a full refresh down the line.


--- Quote from: Old Printer on May 18, 2023, 08:19:43 pm ---The 2200 series were solid scopes and mostly repairable by average people. Later on Tek scopes got pretty involved with hybrid IC's and stored calibration info dependent on built in batteries. Parts for repairs can be a problem, but Tek made a bunch of the 2235's and parts mules are readily available if you can swallow the shipping. When I got my 2225 the front control pots were badly worn and jumpy. I was able to source a late model board from Qtech in Greece and for $50 and a couple hours work my scope was like new..except for the aging electrolytic's that will start to go one of these power ups, but that's not a big deal. Hope you get yours humming.

--- End quote ---

Thanks for the vote of confidence! The more I look into bringing it back into spec the less worried I get. It seems very straightforward just gotta watch those high voltages  :box:


--- Quote from: Arts on May 19, 2023, 02:06:53 am ---
--- Quote from: WhatsICC on May 18, 2023, 06:14:39 pm ---Thanks! I heard so much about the Tek Yahoo Group until they did away with groups, ill make good use of that link.

The store is - Electronic Surplus Industries in North York.
I had to drive a little over an hour from where I am, but this store is just filled top to bottom with testing equipment. Barely any room to walk (in a good way haha)... you can spend hours upon hours browsing

I'm excited to own this 2235, I've read mixed reviews about it but if i can get the traces dialed in ill be more than happy. I hope its just my probe compensation ill have to go out and fiddle with it some more but I dont think it is

--- End quote ---

My own 2235 started acting up a while back. It has always been a great little summer-scope ( I use my ancient Tektronix 547 as my combination winter-scope/shop heater) so I decided to give it a proper tune-up; all of the electrolytics, IEC line filter and associated caps, focus resistors, delete MOSFET connector etc. Good as new now :) 

All you need to know is right here: https://w140.com/tekwiki/wiki/2235

That store sounds like a place I'd like to visit, but it would be a bit of a drive from Montreal..

--- End quote ---

Thank you, and for listing what you swapped! I'll make note, between TERRAs and your info I think Im set :)


--- Quote from: TERRA Operative on May 19, 2023, 05:03:21 am ---My scope is rock solid and great to use, it had some problem with the focus due to drifted carbon composite resistors (a common but easily resolved issue) but after the upgrades in my video linked above, it's working great.

It sits just at a nice point between simplicity of use and good specifications for day to day use.



Re. Arkek, the owner recently passed on so his wife and other staff are picking up the pieces, so while they are still operating AFAIK, be understanding if there are delays on delivering the manuals.

--- End quote ---

I watched your video and am glad I did, great job with that by the way. Very informative and helped give me the confidence to bring another 2235 back to its glory days! haha

Sad to hear about the Artek Owner... but, kudos to his family for stepping up
David Hess:

--- Quote from: WhatsICC on May 19, 2023, 04:32:07 pm ---Much better with DC coupling, I swore I had tried it in DC the night before and it was acting up even setting my ground point to zero then back to dc the 1khz signal was falling well below 0.

However, tried again last night both channels working great in DC! However some funny business going on in the Horizontal Mode and in AC... I'll have to fiddle with it some more, I'm waiting on my signal generator.
--- End quote ---

The difference between AC and DC coupling does not explain why the slope was changing with position and why the intensity control had such an effect.  When results are weird, record the amount of weird.

Using a signal generator in place of the probe calibration signal should reveal a lot more about what is going on.
WhatsICC:
When I get my signal generator I will do a more quantitative test and take record of what's going on.

My first test in AC coupling was done in a quick 20-30 minutes. I'll wait for the scope to fully warm up and do some more involved testing.

I am buying my signal generator from the same location, just waiting for him to get back to me with what he has, I may just do a simple online signal generator and see where it's at. If it's too far off I may see if he'll take it back and work a deal out.

I appreciate the input once again, will update further with more detailed measurements
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