Tektronix 2235 repair thread

[ahmedseecs]

Hi, I have recently acquired a Tektronix 2235A that works fine for couple of minutes but as soon as the oscilloscope warms up the display get defocused. Can you please suggest the possible cause for it.I am quite new it I did try going through the service manual but was unable to understand the cause .
Thanks for your help in advance.
 

[bd139]

Possibly focus pot failing or the divider resistors. See further up this thread for 510k resistors. Very common problem. Replacement pot is fairly unobtainable. I managed to salvage a pot out of another failed scope (different brand) that worked.

Try replacing the resistors first though. Think it’s 4x 510k ones. You need Vishay VR series which are properly voltage rated as there are quite a few bolts across them!

[TERRA Operative]

I managed to find a new and unused pot on ebay a while back, so you might get lucky if you keep an eye out.

Here's the resistors (in blue) I replaced in my 2235, I would replace all 6 if they are present in your unit, just to be safe (resistor are cheap anyway, and it means you don't have to open the scope up for this resistor issue again. )

[Ze Pink Panther]

Good evening everyone,

I hope this thread is not completely dead.
My problem concerns the Tektronix 2235 Service Manual. It is (now) widely available on the net (even fron the Tek web site), but all the versions and copies I've seen have all the same problem: all the folded pages (containing mostly schematics, which makes them even more important and critical) have a scan gap in the middle, which results in column H of the schematics having almost half of it missing.
Can you point me to a source where the SM is _fully_ scanned?

Thanks in advance and regards,
ZPP

[TERRA Operative]

I have a copy of all the 2235 foldouts, available here, along with a bunch of other stuff including high quality scans of the manuals:

https://drive.google.com/drive/folders/1L2ptk_0OeEywzHXIV2jmTQYrtf5IzgIH?usp=sharing

It's the 'Tek 2235 Foldouts large.pdf' file

[Ze Pink Panther]

Thank you, Sir!
You've made my day...

Best regards,
ZPP

[golashki]

Hi, I'm new here and I would like to ask you about repairing 2235

I bought a Tektronix 2235 (a great, beautiful oscilloscope!). Unfortunately, the switch on the "Timing board" PCB is damaged. There is a completely cracked "knob insert" connecting the shaft to the Time Base "A" switch. Unfortunately, as a result of my inexperience, while taking the switch apart, I did not notice that the switches (those brown blocks) have no internal limiters and, additionally, they rotate very easily when the shaft is pulled out. In this way, I lost the "axial alignment" of the complex switch between its elements. The "knob insert" itself can be glued together, but it was problematic to assemble the switch to work as intended.

So I have two questions:
- if anyone can sell the whole "Timing board" for 2235/2236 or the working switch itself (or broken, but not taken apart).
The second beginner's question - is how to disassemble such complicated switches to avoid axial shifts of their position? Maybe someone has such experience and may want to share some proven ways how to fix alignment in multi-module switches, etc.

[David Hess]

The second beginner's question - is how to disassemble such complicated switches to avoid axial shifts of their position? Maybe someone has such experience and may want to share some proven ways how to fix alignment in multi-module switches, etc.

I have done that a couple times and I used the schematic diagram to realign the cams when I put the switch back together.

[golashki]

Yes, unfortunately, the same path awaits me. I thought there is some way to facilitate this procedure. Thanks

[Eduardo Millan]

Hola, tengo este mismo modelo pero esta quemado el Flyback-Se puede conseguir uno nuevo? Gracias

[porter]

Thanks folks for the information.
I replaced  C902-C904 (RIFA), C900, and the Power Input Module on my 2235.

One less thing to worry about.

(My little-screw management skills are not so good. I guy I used to work with told me
that the missing screw count indicates the number of people that worked on something.)