Tektronix 2215 Scope repair

[tautech]

Glad you were able to step back and take another look Vince. 

0.150" pitch for the header ? That used to be a common one.

[Vince]

They are temperature compensating ceramic caps. Otherwise known as dogbones.

Thanks !     Will read up on that...

I guess this explains their form factor then. Being skinny and hollow makes the body "track" ambient temperature more easily. Good airflow and low thermal mass.

[james_s]

I wish I had an easier time staying skinny and hollow

[Vince]

Glad you were able to step back and take another look Vince. 
0.150" pitch for the header ? That used to be a common one.

Sadly for me it looks like is not so common anymore ?! 

I just looked at my two main/local suppliers here, TME and Farnell... none of them have anything suitable ! They do have a FEW 0.15" / 3.81mm pitch board to board connectors, but they are very bulky and weird looking, nothing to do with our thin low profile usual connectors.
Had a look at mouser in the US, just out of curiosity (since I can't buy from them anyway, other than importing), and same as Farnell, all they have is this funky connector model :

https://fr.farnell.com/hirose-hrs/fx30b-4p-3-81ds/connector-header-4pos-1row-3-81mm/dp/2451006

I can't quite believe I am defeated by a bloody connector ?!

I mean if I solder the board back to the main board, without connector, I won't be able to remove it at will to trouble shoot itr and work on it... because once it soldered to the scope, access is horrible and I won't be able to probe anything, never mind replace any component. The board and PCB traces almost survived being separated ONCE... they won't survive it twice or more, that's for sure.  Not to mention the work/hassle it is to remove it, brrr...  27 pins in a single row, double sided, not fun...

So... that's bad news. Now all I can do is solder it back and cross fingers that it still works and that the "dim" trace problem when the delayed time base is enabled, is not located on that little board...

Decidedly, this 2215 is driving me nuts each step of the way !  :-/

I can't believe I am in trouble just because of a bloody connector ! A silly little, humble connector !

Come to think of it, I had the exact same problem when I repaired my 2232 last summer, if you remember ?! No of course you don't remember, just kidding !
I had a bad connector, a wire to board connector, that connects the main board to the big digital board. Was impossible to find a replacement ! I posted on the forum with this specific request, and nobody could find one either !  Luckily I could get a way with it , by soldering the wires of the cable, directly to the digital board. The cable had a (removable) connector at te other end, on the main board, so the digital board could still be unplugged, phew.

So, I guess that's now x2  22XX Tek scopes endangered by obsolete large pitch connectors ?! Starting to make me feel uneasy about these scopes... being at t eh mercy of such a futile little component, how frustrating ! 

[tautech]

As most of the pins are for physical support could that be provided with a bracket/s allowing you to use only the pins that provide an electrical connection ?

Frankenscope ?

[james_s]

Maybe you could replace it with a more commonly available connector and solder that in with a little adapter board or separate wires? I always prefer to find the correct part but sometimes it just isn't readily available and a hack like that becomes excusable. This isn't a priceless collectible that has to stay original inside and out.

[Vince]

thanks for the suggestions... sadly I don' think it would be worth the effort and experience. I mean doing an adapter board would cost money (I can't make PCB in house), and I would still have to find appropriately pitched connectors to solder on that adapter... at least on the mother board side. Yeah on the daughter board side of things, I could make do with individual wires, though I would still have 26 out of 27 of them to wire up ! Just looked at the schematic... there is only one single pin that's unused :-/
Also, all this wiring would add a fair bit of stray capacitance and inductance, can't be a good thing.  That why I liked the low profile header : very short, so very little perturbation introduced.

I guess I will have to give up my connector idea, and just solder it back to the board directly, as it was original, after all 
Luckily it was working fine before, it's only this dim trace problem that bugged me, though was not a shot stopper. I looked at the schematics and I think I do stand a chance that the problem actually comes from the main board rather than the daughter board... we shall see... well assuming I can figure out where the problem lies of course, no guarantee, I am no magician ! 

And then there is still the collet problem, without this tiny little thing, the scope will be missing the time base knob altogether !

Yeah, this scope is definitely a test bed... hardly stellar specs, never going to be my main scope, but boy it has so many problems that I learn a lot from it ! At least from this point of view, it's a success ! 

[tautech]

Forgot to ask Dubbie when he was here last weekend how the collet project for you was going but he'll see these replies and chime in if he's not to busy with his little'uns.

[Vince]

Yeah... don't "pressure" him....

This collet is yet another example of a small part that I thought could be bought off the shelf but is instead ruining a repair attempt.
I enjoy the troubleshooting part, but being stuck because of some stupid little mechanical part, connector or collet or what have you.. it just drives me completely nuts, I have to admit.... 

[Per Hansson]

Hi Vince, spent a couple days reading this magnificent writeup of yours, it's really a nice story!
As for the pinstrip why don't you just cut it into individual pins? You could then just solder them one by one.
Or put them on the delayed time base board (one by one) and link them together with some super glue.
Could even make a small "jig" so that you will get the correct dimension, looking like new that way

As for the collet, do you have exact dimensions of it? If so please PM me and I'll see what I can find
It's my thank to you for this excellent writeup, I have a 2215 too that I will now mod the transformer in.
According to the PDF you posted about further back: SUP3010 M50226

[Vince]

Hi Per,

Thanks for the kind words, and glad my topic is helping you a little bit with your own 2215 ! 

As for the pinstrip why don't you just cut it into individual pins? You could then just solder them one by one.

Yeah, I did think of that, as a last resort... but sadly the pins are way too big to fit into 0.1" contacts, it's like giving the Yeti shoes from a 5 year old... it's never gonna do it !...

I guess I could also replace the pins on the board one by one, by matching 0.1" pins, right angle... talk about a job ! Also, they would have to be extra-long pins, otherwise they won't clear the edge of the board.. not sure this kind of header is readily available, would have to check.

As for the collet, do you have exact dimensions of it? If so please PM me and I'll see what I can find

Do you have some collets in stock ? Problem is they seems to all have different shapes and sizes, they are custom for every Tek scope or pretty much 

Still, doesn't hurt to have a look at your stock. I created a thread about this collet, a couple months back, you can read all about it there :

https://www.eevblog.com/forum/repair/searching-for-a-18-collet-to-repair-a-tek-sweep-knob/

I put a drawing of the collet with pictures.

Dubbie and Tautech are kindly teaming up to try to make one, at the other end of the world in New Zealand. Let's see how it turns out (no pun intended  )... will it be doable... will it be a nightmare of a job and we must give up... I don't know just yet...

[Per Hansson]

No collets in stock but I work for a company that sells & services lathes and mills
But it seems you have come quite far already, I read the thread you linked

As for the pins some can be bought without the strip too, but need some measurements then.
I.e. something like this: https://www.elfa.se/en/dil-socket-tec-pin-003-95/p/14817813

[Per Hansson]

I'm curious about the Rifa death caps though Vince, did you not replace yours? I have ordered them too, same partno was still available at Elfa LOL

[Vince]

I'm curious about the Rifa death caps though Vince, did you not replace yours? I have ordered them too, same partno was still available at Elfa LOL

Well... have to say I don't know what you mean by "Rifa" cap, never heard that term before.
OK let me Google it... Oh OK, I see... that's the name of the manufacturer for these squarish semi-transparent yellowish mains rated caps I see in many products.... didn't know they had a nick name !

No I didn't replace them since they clearly were not the issue, and didn't show any visible sign of damage.
Also, I thought these mains caps were precisely super ultra reliable, precisely because there meant to be used on the mains, so I assumed I should never have to worry about these type of caps.

Well that was what I used to think up until very recently... but I watch lots of repair videos from various people, and it appears these caps can indeed go bad in old device, to my surprise ! And actually, no later than later last night/early this morning, I was watching a repair video from a channel I am subscribed to : "Artifact Electronics". The guy was repairing an old TRS-80 8 bit computer, and during this very repair, a "Rifa" cap in the SMPS released the magic smoke !!! 

https://youtu.be/gVtp0YuLP94?t=731


So yeah, at least now I know this type of cap can fail...

[tautech]

Rifa's are used in the incoming mains filter X-Y network, they are an old brand name and the other common one to fail is Schaffner filters. Either create a bit of smoke, stink and sometimes a blown fuse and if you're unlucky some localized damage. For a bit, equipment is perfectly capable of running without mains input filters although their usage also manages SMPS noise being emitted onto the mains.

[Vince]

Shaffner ! Ah yes, this one rings a bell, I learned about it just a few days ago ! Someone on Tekscope ISTR, having problem with a 2215 SMPS again, IIRC !   

I need to do some reading on X Y caps... am gathering bits of info here and there on YT as I watch more and more repair videos.

Well simply knowing they are called X and Y caps is already something  ! 

Then if I am not mistaken, the letter X or Y refers to how they are wired on the mains. "X" means the cap is straight across the live and neutral wires, so if this one goes bad it can of course short the mains ! Scary...

Then the ' Y ' caps always come a pair : a common point tied to the earth wire, then one cap goes to neutral and the other to live.

So there are two use cases, I guess each with its own set of design criteria, so the physical presentation of X and Y caps is different.

So this Rifa, squarish caps for ' X ' use, or other squarish looking molded film cap.
As for ' Y ' usage, from what I gather, they are usually disc ceramic caps. Either the old fashioned "brown" disc caps, in very old equipment, or on more recent gear, a thick, blue coloured disc.

That's about all I know for now. What I need to figure out among other stuff, is I see sometimes a digit appended to the letter : X1, X2, Y1, Y2.. something like that. I need to figure out what that means...

[lordvader88]

I own this scope and it's my 1st analog scope. Sometimes I think it has issues, but I don't really know for sure, I need more experience.



How complicated to work on, is this era of scopes compared to ones full of processors in the 80s ? I love the older stuff, it's so much more "hands on" so to speak

[james_s]

I just worked on a 2215A the other day, they're incredibly simple compared to most scopes I've been inside. I was actually surprised at just how little is in it.

[particleman]

The 2215 is essentially one big board compared to a 4 series scope which are a cube of boards around more boards. On the 2215 just slide out the CRT and remove the attenuator/sweep board and  you have full access to everything.

[james_s]

One warning I can give about the 2215A, don't wash the V/div knobs in an ultrasonic cleaner! I did that because they were totally gross and indeed they came out squeaky clean. So clean that there's no trace of the printing that was on the transparent portion! So if anyone has a pair of those knobs for a modest price let me know. Alternately a good scan I could print on transparent waterslide would probably work. The scope is far from pristine and has some other issues so it's not worth investing a lot but it's a Tek so I can't bring myself to junk it.

[Vince]

One warning I can give about the 2215A, don't wash the V/div knobs in an ultrasonic cleaner!

"Luckily" I don't have the luxury of an US cleaner, so just good old detergent and brush for me, works fine. Thanks for the warning though, as I sure intend at some point, to get an US cleaner...

So if anyone has a pair of those knobs for a modest price let me know.

I feel for you. I need to buy some broken knobs for my 2232. Looked at Sphere and Qservice, the main suppliers.... lessons learned : knobs on these scopes cost a fortune, assuming they are even available at all. IIRC the Volts/dic knobs were available on Sphere, for an insane amount of money, the you double it to import it to Europe in my case. If you are in the US at least you get cheap shipping so it's not so bad.

As for scope smiplicity, this 2215 is simple but somehow I find the more modern CRO TDS scopes, much simpler and easier to work on. My TDS 544A was a joy to work on, with two large board where everything is there accessible, for you to probe at will, while the scope is running.

The award goes to my TDS 310 (or any TDS 300, all the same) : there is just one tiny main board the size of your palm, which contains everything, and then just the front panel board which can be popped out easily and again, be probed at will while the scope is running.   A joy.  Only problem with the SMPS which is quite complex and third party so no schematics available, never mind a service manual. I have to repair one and it's not fun.. still not diagnosed. Might come back to it one day...

The scope is far from pristine and has some other issues so it's not worth investing a lot but it's a Tek so I can't bring myself to junk it.

Yeah same here.. mine is in good nick overall, but not worth investing money in it... but as you said it's a Tek, not some no-name crappy hobbyist level scope that flooded the market in the 80's an '90's... so I do what I reasonably can to sort it out...

[Vince]

I own this scope and it's my 1st analog scope. Sometimes I think it has issues, but I don't really know for sure, I need more experience.

Just start a topic of your own so we can help you out more efficiently... otherwise this thread will become confusing and unmanageable.
Post a link here to your thread once you have created it, will see you there...

How complicated to work on, is this era of scopes compared to ones full of processors in the 80s ?

Well actually the 22XX scopes ARE from the '80's... so not sure what you mean ;-)
The ones with processors are for example the 2232 because it's both analog and digital at the same time. There is a processor board that handles the digital/storage stuff, but it's a standalone board. The scope is otherwise a "normal" analog scope like this 2215 scope or friends. So you don't have to actually worry about the "processor stuff"... you can just treat them as a regular 22XX scope. Once the analog part of the scope is working, you can work on the processor  board if need be, but only if need be. A dead processor will not keep the scope from working as a regular analog scope. It's a very modular/fail safe design, I like that...

If you have in mind the more complex analog scopes of the day, the 2445/2465/2467 etc, then yeah they are much more complex and are designed from the ground up around a processor. So if anything is wrong with the digital  part of the scope, you are in trouble. They definitely are not the best choice to hone your repair skills. The old 22XX scopes are indeed a much better choice. All discrete components, readily available for the most part, great service manual, low component density/easy to probe...  it's definitely a good place to start, I think !  It will give you a good understanding of how a scope works, and train your brain for trouble-shooting. Then you can move up to more complex scopes, with surface mounts stuff, higher density and more digital stuff, if you wish.

I love the older stuff, it's so much more "hands on" so to speak

Yeah 

[Per Hansson]

MOSFET

So one thing leading to another.. the legs of the old FET, broke as I had to bend them to put the FET back into its plastic holder/box. Didn't think that soldering the pins would be very elegant nor anything to be proud of, so I took that opportunity to replace the FET with the modern replacement I had bought. I didn't find the usual IRF something model, so had to improvise and just use a parametric search and pick what might be suitable... I stumbled on some weirdly named part I had never heard about, it's a IPP60R280P7  made by Infineon... I thought these guys only made memory chips ?! Apparently not... you live and learn.

This part as one would guess, is at least no paper much better than the old IRF820, which was 2.5Amps and 3.0 ohms RDSon. The Infineon part can sustain at least 8 amps, and RDSon is literally an order of magnitude lower, at 0.28ohm. Sounds almost too good to be true, but well, they had the guts to put that in their datasheet so I guess there must at least some truth to it ! Hell, even if it's only half as good as they say, it would still be much better than the old IRF820 !

Have you looked at the gate waveform after this change? (Tektronix measure point 25 in the schematic)
Here are three different examples I tried on my A18 board with a 1A load, as you can see there is a quite nasty dip in the miller plateau.
I suspect it is because the newer MOSFETs have much higher capacitance, so C921 needs to be scaled up.
Either that or add some resistor on the gate, so it does not pull down the PWM output so much.

[Vince]

Have you looked at the gate waveform after this change? (Tektronix measure point 25 in the schematic)

Nope. Looked at it briefly as I was trouble-shooting the SMPS initially, but haven't looked at it again once I had replaced the FET with something else.
It just worked and did not overheat so I moved on to the other problems that need to be addressed.... which are much more complex than the SMPS.

This auto-brightness feature in the 2215 is just driving me completely nuts, I am pulling my hair out, losing appetite, losing faith in the ancient Greek God " Elektron ". Spent whole day last Saturday, working/probing the scope... so I made some progress, but still far from a diagnosis... maybe because this scope is acting so erratically that I am still in the process of figuring out WHAT exactly are the true symptoms.... trying to make sense of its weird behavior, trying to see the "signal" in all that "noise" of symptoms.... is not yet fully achieved I am afraid.

I am not giving up just yet, but I think I will not spend too much time on it (other stuff on my plate), because I had a look at the service manual for the 2215A scope, the revised/improved version of this 2215 scope... and came to realize that the only thing they changed on it, spec/feature wise.... the only user visible change they made... was to DROP this auto-intensity "wizardry" altogether ! They didn't even try to fix it, they just gave up completely on it, to the trash !
So I think if Tek themselves gave up on it.. it must be really, really hopeless, and I am basically wasting my time trying to get to work, something that most likely never worked properly even when new back in the day !   

So I will not be losing sleep over this 2215...

I am not out of leads/ideas just yet, and I hate being defeated, so I am still working it for now... but I also know that it will probably never "just work", so I won't try to make it perfect. Just trying to get rid of the most blatant/inexcusable problems with it, as I am hoping that at least these bits I have a decently reasonable chance of fixing. But I will not spend 10 years trying to iron out every tiny little quirk, because they probably existed even when it was brand spanking new ! 

Here are three different examples I tried on my A18 board with a 1A load

Thanks for sharing your experiments.

as you can see there is a quite nasty dip in the miller plateau.

Don't know what is meant by "Miller Plateau", will need to read up on that.
I do see however the dip, in the middle of the leading edge, getting deeper and deeper  as we compare the successive graphs...
is that really of concern ?

[tautech]

Yes, it is !
It can possibly lead to the MOSFET gate drive dipping below levels needed to maintain an ON condition.
See the screenshots and the leading edge dip.