Just got a Tektronix 2235 (Opt 1)

[vulturebetrayer]

I found the original datasheet and original manuals online for you.
I have linked them here:

https://vulturebetrayer.com/tektronix2235.html

I have hotlinks disabled on my site which is why I had to make a page for you.

edit:
spelling fail

[David Hess]

I am sorry if I was not clear and just to avoid confusion, I was referring to the datasheets for the capacitors.  The 2235 service manual has the capacitor part numbers but to find their ESR and ripple current ratings, the datasheets for the capacitors will be necessary.

But again, they are not that critical; capacitors intended for low ESR high frequency switching regulator applications will work fine.  I would probably use the Nichicon PW series for the output capacitors and maybe for all of them but there are other higher performance choices.  Increasing the voltage derating to get larger case sizes will help with meeting any ripple current requirements.

Also in 1990 when the 2232 was released, the 2235 and 2236 became the 2235A and 2236A with uprated parts lists so the 2235 and 2235A are not quite the same.

[vulturebetrayer]

I am sorry if I was not clear and just to avoid confusion, I was referring to the datasheets for the capacitors.  The 2235 service manual has the capacitor part numbers but to find their ESR and ripple current ratings, the datasheets for the capacitors will be necessary.

But again, they are not that critical; capacitors intended for low ESR high frequency switching regulator applications will work fine.  I would probably use the Nichicon PW series for the output capacitors and maybe for all of them but there are other higher performance choices.  Increasing the voltage derating to get larger case sizes will help with meeting any ripple current requirements.

Also in 1990 when the 2232 was released, the 2235 and 2236 became the 2235A and 2236A with uprated parts lists so the 2235 and 2235A are not quite the same.

ahhh so we would need to know the exact cap model for that device and what year and model it was specifically. . .
 oh well, worth a shot I guess

[R005T3r]

It's in pretty decent condition but unfortunately the Volts/Div knob is missing 1/3 of its backplate.(see attachement)
If someone knows where I could find a replacement knob please give me a clue.
There's a service center for old Teks in my country but doesn't have one in stock.

If you have access to a 3D printer or know someone who does, fabricating a replacement could be unsightly yet serviceable solution while you search for an official part.

Actually there's a simple way to fabricate your own parts: silicon molds and resin. Also, you will need someone who make the design for the printer and it's not that simple... Since the object is not too small, and considered the knobs are identical, I think it's the easiest way to have the replacement. Also you will have:
1. a greater level of detail than 3D replicated stuff (to help you understand how good it is, you can clone miniature soldier out of that with the finest details printed...)
2. You can also load the resin with colors if you want or other agents to make it heavier, shinier and glittered...
3. there are many types of resins with various characteristics and proprieties.

[belzrebuth]

I'm waiting for a friend to decide what he also wants from TME and then we will place an order.

I think PWs should be fine for the task .Their specs are decent and they are rated specifically for switching psus.
PWs are also much cheaper than Panasonic FCs (not that cost matters for this kind of repair)
Here's what I plan to order:
http://www.tme.eu/gr/details/upw1e102mhd/puknote_-ilektrolut-tit-chamil-antist/nichicon/

Would it be a wise choice to replace every electrolytic in that section or just try my luck with these six?

Also,is there any trick to remove the psu shield?!
I've removed the screws but it's somehow stuck in there.
Maybe remove the little pcb in front of it?The one with the soldered leg-pins.

@vulturebetrayer Thanks a lot for these files and for your time iploading them!

@David Hess You've been a great help so far.Thanks!

While the soldering looks factory I think the caps on mine have been changed..
I saw pictures of another 2235 supply and the originals should be mallory brand and 840uf at 12V.


@R005t3r
I think I'll just wait for a replacement to appear.
I don't have a 3d printer or access to one but even if I did I wouldn't bother since ,as you say, it might be more difficult than one would think.

[David Hess]

Would it be a wise choice to replace every electrolytic in that section or just try my luck with these six?

Replace them all since you will have access.

Also,is there any trick to remove the psu shield?!
I've removed the screws but it's somehow stuck in there.
Maybe remove the little pcb in front of it?The one with the soldered leg-pins.

I cannot say since I have never had mine that far apart or it was so long ago that I do not remember.

[oldway]

Power supply of 2235 is working very hot and I recommend to install a fan.
Look at the schematics of the 2236 to see how to do it.
This is still more important because you live in a place where the weather is quite warm.

[belzrebuth]

Yes I read somewhere that there's even a connector for a 12V fan on the board.(for the 2235A at least).
Mine has the fitting ready in the chassis but I don't know where the connector is.
I'll try to find where I read about it and maybe I have the same connector.
I think I'll probably do that just after I install the new capacitors and check for good operation.

If only I could take that PSU shield off!
I need to write down the values of the other caps in the board but the shield just won't let me see.

[belzrebuth]

Okay I got the shield off.
The pcb that connects to the board in front of the power supply is almost impossible to remove (gently at least) so I tried to remove the shield without disconnecting the pcb.

I eventually did it but I think there should be an easier way.

Anyways the six caps I mentioned earlier are definitely looking bad.

I've also got a 330uf 50V cap (C956) that I'm going to replace because it's "IC" brand ,same with the other bad caps so I doubt it's ok.
There is a nippon 1000uf 50V cap that looks ok.(c940 or 941)

And there are three other capacitors at the right back that their voltage values I can't see.(c942 / c943).These look okay too.

There's one (c954) right next to the 330uf cap that I think it's 33uf but with high voltage rating.(200V maybe)

And the last electrolytic in this section is a C925 whose voltage value also I can't see.I think it is 100uf but can't see a thing the way the chassis gets in the way.

[belzrebuth]

Anyone's got experience with Chemi-con KYA series?

A local store has them in stock so I thought I could replace the 1000uf 25V with these instead of PW because I can get them today and finally enjoy my scope!
Should I wait a week or so for PWs or these could also do the job?
I'm thinking out loud here but I could get those and check if the problem is indeed the blown caps and then order PWs for the whole supply board..

[belzrebuth]

Okay!
Scope's okay now.
Replaced the 1000uf caps and the 330uf cap and the trace is now crisp with no noise even at the mV range.

Surprisingly putting the power supply shield back was far easier than removing it!
Thanks everyone:)

(if anyone need any pictures let me know)

[David Hess]

The Chemicon KYA series will work fine except for the input capacitor to the switching preregulator which needs to be higher voltage.

[tautech]

Well done. 

2 pics of the display showing before and after would be good for anybody finding this thread in the future.

[belzrebuth]

Which capacitor is the input cap to the preregulator?
The 33uf 200V?(I have one 33uf next to the 330 which might be 200V but I couldn't see well,I need to desolder it to check its ratings )


I intent to order chemicon PWs just in case I go paranoid and decide to re-recap everything but unfortunately when I opened the unit I couldn't see the values of some of the caps the way they are put in place.
I wouldn't want to desolder them and put them back so I could just wait for something to fail again before messing again with the insides of the scope.

I have one question though.
I see the trigger led randomly lighting up with nothing connected.It does that every 40s or so.
The traces dissappear for maybe hald of a second and then come back.
What could be causing this?

@tautech:pics are on the way..

[David Hess]

Which capacitor is the input cap to the preregulator?
The 33uf 200V?(I have one 33uf next to the 330 which might be 200V but I couldn't see well,I need to desolder it to check its ratings )

It is C906 which is marked 75uF on the schematic and 450V in the parts list; it is the big one on the right side of the power switch from the front.

I have one question though.
I see the trigger led randomly lighting up with nothing connected.It does that every 40s or so.
The traces dissappear for maybe hald of a second and then come back.
What could be causing this?

That is normal when there is no trigger available.  What happens is that occasionally when no trigger is available in AUTO mode, there will be enough noise to cause a trigger but this resets the trigger timeout and without further triggers, the display will be blanked until either a valid trigger occurs or the trigger timeout finishes.

[belzrebuth]

Thanks again David:)
I'm a total noob regarding oscilloscopes but that's the reason I got one (one has to start from somewhere!)
One thing I noticed is that I left it on for sometime and got hotter than before;maybe it's just me or just the ambient temperature is higher than yesterday.
Here are some pics with the same settings (volts/div fully clockwise and 20us timebase)
The difference is obvious.
And bonus audacity generated 1khz sine

[David Hess]

I'm a total noob regarding oscilloscopes but that's the reason I got one (one has to start from somewhere!)

The 2235 is a great oscilloscope to start with and actually at the higher end of the features curve with delayed sweep capability.

One thing I noticed is that I left it on for sometime and got hotter than before;maybe it's just me or just the ambient temperature is higher than yesterday.

The original design lacked a fan and I am not aware of any heat related issues.

[oldway]

I am not aware of any heat related issues.

In fact, there is a big one: internal isolation failure between layers in the pre regulator transformer (in reality, an inductor) T906 (120.1439-00) for working a long time at to high temperature.
As this transformer is no more available, the oscilloscope with this fault is not repairable

[belzrebuth]

I am not aware of any heat related issues.

In fact, there is a big one: internal isolation failure between layers in the pre regulator transformer (in reality, an inductor) T906 (120.1439-00) for working a long time at to high temperature.
As this transformer is no more available, the oscilloscope with this fault is not repairable

I'd be interested in installing a fan on mine as I indeed live in a quite hot area and that can't be good for my scope.
Some info that I got online  states that I need a 12V 60x60mm maybe SUNON brand like the ones found in servers.
There is also a blog post about it but the author doesn't describe the whole process well enough imo.
http://blog.cluepusher.dk/2011/02/16/simple-fan-mod-for-tektronix-2235/

If you have more information (a short guide maybe?!) please share..

[oldway]

You must download the service manual of the 2236 and look at the schematics.

http://elektrotanya.com/tektronix_2236.pdf/download.html

[belzrebuth]

So I check the 2236 schematics and "copy" its fan circuit to the 965 area of my 2235.
Correct?

[David Hess]

I am not aware of any heat related issues.

In fact, there is a big one: internal isolation failure between layers in the pre regulator transformer (in reality, an inductor) T906 (120.1439-00) for working a long time at to high temperature.
As this transformer is no more available, the oscilloscope with this fault is not repairable

I am aware of problems with the preregulator transformer/inductor from discussions over on tekscopes@yahoo.com but have never tracked down the actual failure mode.  They do not develop open or shorted windings but appear to have low inductance so my hypothesis has been either a cracked core or a material change do to overheating.  I myself have never gotten ahold of a bad 22xx to test; all of mine work fine.

[David Hess]

So I check the 2236 schematics and "copy" its fan circuit to the 965 area of my 2235.
Correct?

That is basically it.  There is not much to it.

There were some variations in the series in how the fan was setup but any of them will work.  The 2230, 2232, 2236, and 2236A schematics cover most if not all of what is needed.  The air volume is pretty low so a slow fan will be more than adequate.

[belzrebuth]

Okay.I'll see what I can do.
I'll probably order a SUNON fan like the ones used in servers and check the schematics in the meantime.

[David Hess]

I found my old tekscopes@yahoo.com post about the 2-channel 22xx fans:

1. The 2213A, 2215A, 2235, and similar models which lack a storage or
counter/timer/multimeter (2236 and 2236A) board lack the fan power
circuits and fan.  From what I remember at least on the 2235, the main
printed circuit board (A1) is the same but lacks the parts so the fan
is easy enough to add if desired.

2. The 2230 and early 2232 and similar power the fan from the +8.6
volt supply with a parallel set of rectifiers and an RC decoupling
network.

3. The 2236 which has the counter/timer/multimeter in place of the
digital storage board powers the fan from the difference in the +5 and
-8.6 volt supplies with a parallel set of rectifiers (3/4 wave?) and
an RC decoupling network.  Maybe the 2236 ran hotter than the early
2232?

3. The late 2232 (and 2235A and 2236A?) powers the fan directly from
the difference in the +5 and -5 volt supplies and includes the same RC
decoupling network (2.7 ohms and 4700 microfarads) as the early 2232.

That makes for 8.6, 10 and 13.6 volt supplies for the fan depending on
model.  I have never encountered a 12 volt DC brushless fan which
would not operate over that range of voltages.