Tektronix 465 timebase-knob issue

[xtoffer]

Hello!

The timebase knob has been acting up lately causing it to skip steps when changing direction. I have been meaning to fix it for awhile but only recently aquired the right tool  to remove the knobs. Aaand additionally, it has finally failed completely.

Anyways, as expected it turned out to be a mechanical issue. The first (longer) plastic cylinder had broken off right after the cogwheel that makes the clicking indents. Fortunately it was easily glued, and as there is not much strain there I expect it to last quite some time.

Although this (the main timebase functionality) now works again, there was still some additional resistance when turning the knob. This came from the additional functionality part (the one that changes when pulling the knob and turning). After having a closer look at that part I found some broken pieces of plastic in there as well. I got them all out and as they seemed rather glueable as well, I attached them as I think they they were before breaking off. See the picture with the cylinder, spring and wingy plastic thingy. The wings of the plastic thingy fits into slots in the cylinder when pulled far enough.

Here is also (finally) my problem. When assembled and pulled the second cylinder now also turns as supposed to, however when not pulled it still is not pushed out far enough out of the slots to not turn the cylinder. By my estimation it needs another 1-2mm. The limiting factor is what protrudes from the pot but I cannot find anything that's adjustable enough to provide the extra space.

So I am looking for some input. Maybe someone has been there already and seen the mechanism and can tell me if I have assembled it correctly. Maybe I added some length when glueing it together, but I have a hard time believing that I added a mm. I could possibly also scrape some off the wings, but I'd rather not

I'll appreciate (almost) any input

[femtohertz15]

I think it looks like a tiny Oldham coupler.   You might find new ones on sdp-si.com and mcmaster.com, but not cheap.   I don't know where to get cheap ones.  Or of course a big box of replacement parts (eg another 465).

Its boggling that a 40 year Tek scope has failed on mechanical issues!

[rqsall]

I have a bunch of pictures (if I can find them) and notes (emails and tekscopes yahoo list posts actually) that may be helpful to you from when I fixed mine. Although mine didn't desintegrate as catastrophically as yours seems to have done. But you'll have to wait until I get home from work this evening.

But to get you going: i'm pretty sure that steel shaft is not supposed to be able to be separated from the rear drum.

[xtoffer]

I think it looks like a tiny Oldham coupler.

Googled the name, it seems you're right. That part looks rather intact though. Except, of course, if it somehow has gotten streched. But I think (and hope) not. Have loosened all the screws to try to find some adjustment but there seem to be no length to give.

Its boggling that a 40 year Tek scope has failed on mechanical issues!

I find it rather amazing as well that it still works (worked) and can provide value. I got it just a few years back and have no clue how many times it may have been repaired before of course. And although it has some other minor issues, most of the functionality is (or was) there! When powered on for a bit longer there sometimes appear some artefacts on the screen, I suspect some kind of heat issue. If I get this working well enough I'll probably have a look at the fan as well.

I have a bunch of pictures (if I can find them) and notes (emails and tekscopes yahoo list posts actually) that may be helpful to you from when I fixed mine. Although mine didn't desintegrate as catastrophically as yours seems to have done. But you'll have to wait until I get home from work this evening.

Pictures might be helpful! I have searched quite a bit but haven't found any of this part disassembled. There are also some exploded drawings in the scope manual, but I didn't find one with a good enough closeup of that either.

But to get you going: i'm pretty sure that steel shaft is not supposed to be able to be separated from the rear drum.

The steel shaft in the picture is the middle of three steel shafts of the whole knob construction. The outermost ends in the first longer gray plastic cylinder. The middle goes all the way through until it hits (in my case) the oldham coupler (thanks for the word), but should not connect to it. The innermost also goes all the way through but connects with the oldham coupler, by two screws. (The fine adjust/uncal one.)

If by rear drum you mean what I refer to as "gray plastic configuration cylinder thingy", you might be right and something else also broke off that I didn't find. But it seems that in my case it doesn't come out far enough.

[xtoffer]

The potentiometer at the end of the shaft looks as if it has received some attention at some time in the scope's history. I would guess that the timebase knob has received an impact from the front that has pushed back the whole shaft and the potentiometer. This would account for the damage to the plastic components. If you re-align the potentiometer I suspect you will find that all the other parts of the knob and shaft will line-up too.

Well spotted! But I'm afraid that is my doing, tried to see if the soldered connection had something to give and forgot to mention this. The connections on the side are desoldered in an attempt to align it, however so far unsuccessfully. This might still be possible, I think I will try this again tonight. There are three pins on the bottom side soldered to the PCB and a plastic spacer between the pot and the board as a standoff for the height.



Edit: Nah, the pot to board connection is rather snug, doesn't budge enough... something has to!!

[rqsall]

I finally manage to find the time to dig in my mail history and other assorted notes.

There's some information and pictures here: https://forum.tek.com/viewtopic.php?t=138253

In the attachment you can see the rear drum with the shaft sticking out of it. you shouldn't be able to separate them unless something inside is broken.
There's a cylinder inside the rear drum. I'm going to quote from a tekscopes post:

The (Al) central axle normally rotates a cylinder with longitudinal outer ridges (i.e. running in parallel to the axle). Around this cylinder, the switch drum sits. The ridges grip the switch drum, allowing the axle to rotate the drum.
The construction allows longitudinal movement of the cylinder inside the switch drum. This movement is spring-loaded. This is (partially) what happens when you pull the gray time base knob.

The rather vulnerable construction sometimes starts allowing the plastic drum to slip on the thin axle, resulting in the non-detent feeling that you describe.
This can be fixed as follows:
After removing the axle-cylinder-drum assembly and holding it drum-down, it is possible to apply some cyano-acrylate glue, letting it run down along the axle, toward the axle-cylinder interface. Causing a short and slight forced slippage allows more glue into the axle-cylinder interface. Any more than a very slight amount of glue will allow it to spread sideways onto the cylinder-drum interface.

I repaired mine with this method. You need to let the glue in from the back of the drum, not from the side you see in the picture I attached. But it seems yours is further gone, and you may need to go the route of the forum.tek.com post: https://forum.tek.com/viewtopic.php?t=138253

[Andy Watson]

I think it looks like a tiny Oldham coupler.

Googled the name, it seems you're right. That part looks rather intact though. Except, of course, if it somehow has gotten streched.

Something has been bugging me about that photo and I've just realised what it is. The Oldham coupler is missing a section. There should be a central section that resembles a disk with a slot in each side - the slots being 90 degrees relative to each other.

[xtoffer]

I finally manage to find the time to dig in my mail history and other assorted notes.

There's some information and pictures here: https://forum.tek.com/viewtopic.php?t=138253

In the attachment you can see the rear drum with the shaft sticking out of it. you shouldn't be able to separate them unless something inside is broken.
There's a cylinder inside the rear drum. I'm going to quote from a tekscopes post:

The (Al) central axle normally rotates a cylinder with longitudinal outer ridges (i.e. running in parallel to the axle). Around this cylinder, the switch drum sits. The ridges grip the switch drum, allowing the axle to rotate the drum.
The construction allows longitudinal movement of the cylinder inside the switch drum. This movement is spring-loaded. This is (partially) what happens when you pull the gray time base knob.

The rather vulnerable construction sometimes starts allowing the plastic drum to slip on the thin axle, resulting in the non-detent feeling that you describe.
This can be fixed as follows:
After removing the axle-cylinder-drum assembly and holding it drum-down, it is possible to apply some cyano-acrylate glue, letting it run down along the axle, toward the axle-cylinder interface. Causing a short and slight forced slippage allows more glue into the axle-cylinder interface. Any more than a very slight amount of glue will allow it to spread sideways onto the cylinder-drum interface.

I repaired mine with this method. You need to let the glue in from the back of the drum, not from the side you see in the picture I attached. But it seems yours is further gone, and you may need to go the route of the forum.tek.com post: https://forum.tek.com/viewtopic.php?t=138253

Yes! Thanks, I am sure I was on this page at some point but completely missed what I was after. These are indeed the right pictures and it seems he had the same problem. A brass replacement of the plastic thing of course looks much better than my glued remains of plastic bits. It also seems I have assembled it correctly according to the pictures of that one. Whether it is bad that it is able to come out the whole way I am not sure about but the slots inside the drum seem intact as well and the winged plastic key thingy can turn it properly when inserted.

I also realised that I had misunderstood the workings slightly, the post seem to confirm this as well. I believed that the normal timebase switching was just the first cylinder moving. (Somehow it didn't make sense in my head that the extra functionality should always be moving :p Makes it harder to turn etc.). It seems I was wrong and I believe now that both cylinders should move normally and that the first one just stops on pulling. This means that there is no length problem, just the issue of assembling it correctly again, with everything aligned. Hints are very welcome!

I think it looks like a tiny Oldham coupler.

Googled the name, it seems you're right. That part looks rather intact though. Except, of course, if it somehow has gotten streched.

Something has been bugging me about that photo and I've just realised what it is. The Oldham coupler is missing a section. There should be a central section that resembles a disk with a slot in each side - the slots being 90 degrees relative to each other.

Hmm, not sure what you mean, got a picture? I do not have much to compare it to, the one in the post linked above looks different (http://www.ps-service.cz/tek/finale3.jpg). Like a more solid metal package. Maybe there are different versions of the board, or it has already been replaced at some point? I cannot fault the oldham coupler though, it screws in and turns properly. It is basically the connection between the pot and the innermost metal shaft that goes to the fine adjust of the timebase ("uncal knob").

[rqsall]

I also realised that I had misunderstood the workings slightly, the post seem to confirm this as well. I believed that the normal timebase switching was just the first cylinder moving. (Somehow it didn't make sense in my head that the extra functionality should always be moving :p Makes it harder to turn etc.). It seems I was wrong and I believe now that both cylinders should move normally and that the first one just stops on pulling. This means that there is no length problem, just the issue of assembling it correctly again, with everything aligned. Hints are very welcome!

Alignment is just to put the drums in the black square brackets and turning them to where they lock. Then assemble the drums on the board. Make sure you put them both in the right way up. I had one upside down and then the time base knob works in the wrong direction.  I had to take the entire thing apart again... 

Good luck!

[Andy Watson]

Hmm, not sure what you mean, got a picture? I do not have much to compare it to, the one in the post linked above looks different (http://www.ps-service.cz/tek/finale3.jpg). Like a more solid metal package. Maybe there are different versions of the board, or it has already been replaced at some point? I cannot fault the oldham coupler though, it screws in and turns properly. It is basically the connection between the pot and the innermost metal shaft that goes to the fine adjust of the timebase ("uncal knob").

This is the best picture I can find (Wiki). You appear to missing the black piece in this photo:

https://en.wikipedia.org/wiki/File:Klauenkupplung_3.jpg

I've just slipped the cover off my 475 to grab a photo but it doesn't have an Oldham coupler, nor a any flexible joint. It uses a straight-through coupling of approximately 0.5" length.

[rqsall]

Hmm, not sure what you mean, got a picture? I do not have much to compare it to, the one in the post linked above looks different (http://www.ps-service.cz/tek/finale3.jpg). Like a more solid metal package. Maybe there are different versions of the board, or it has already been replaced at some point? I cannot fault the oldham coupler though, it screws in and turns properly. It is basically the connection between the pot and the innermost metal shaft that goes to the fine adjust of the timebase ("uncal knob").

This is the best picture I can find (Wiki). You appear to missing the black piece in this photo:

https://en.wikipedia.org/wiki/File:Klauenkupplung_3.jpg



I've just slipped the cover off my 475 to grab a photo but it doesn't have an Oldham coupler, nor a any flexible joint. It uses a straight-through coupling of approximately 0.5" length.

I don't see anything amiss with the coupling in xtoffer's 465. This is mine:

[Andy Watson]

I don't see anything amiss with the coupling in xtoffer's 465. This is mine:

I think you're right. Your photos show that the plastic in the middle is one piece - I had assumed this was the tangs of a slotted coupler.

[xtoffer]

I don't see anything amiss with the coupling in xtoffer's 465. This is mine:

I think you're right. Your photos show that the plastic in the middle is one piece - I had assumed this was the tangs of a slotted coupler.

Mm looks like mine is similar to rqsall's.  Anyhow good, one less thing to worry about

I also realised that I had misunderstood the workings slightly, the post seem to confirm this as well. I believed that the normal timebase switching was just the first cylinder moving. (Somehow it didn't make sense in my head that the extra functionality should always be moving :p Makes it harder to turn etc.). It seems I was wrong and I believe now that both cylinders should move normally and that the first one just stops on pulling. This means that there is no length problem, just the issue of assembling it correctly again, with everything aligned. Hints are very welcome!

Alignment is just to put the drums in the black square brackets and turning them to where they lock. Then assemble the drums on the board. Make sure you put them both in the right way up. I had one upside down and then the time base knob works in the wrong direction.  I had to take the entire thing apart again... 

Good luck!

Ugh, yeah that's rough. The cogwheels on mine have little red markings. Turned them all the way in one direction and they seem to line up. Had some time to reassemble and I think I managed to align the main things, bit easier than I first imagined. Not entirely sure about the thing between the coupler and the cylinder though. Only thing it can do is limit the turning somehow.. need to look up how that is supposed to work.

Really need to get this together soon, in its current state it occupies most of my precious bench space!

[rqsall]

Ugh, yeah that's rough. The cogwheels on mine have little red markings. Turned them all the way in one direction and they seem to line up. Had some time to reassemble and I think I managed to align the main things, bit easier than I first imagined. Not entirely sure about the thing between the coupler and the cylinder though. Only thing it can do is limit the turning somehow.. need to look up how that is supposed to work.

Really need to get this together soon, in its current state it occupies most of my precious bench space!

When the drums are fully locked counter-clockwise, the knobs (both ) also need to be at the slowest time base settting of course. The spring thingy at the back relates to the text on the front "A only' and/or "Only when knobs locked" (never could figure out which and I forgot which one I used to set it, it's not critical). It prevents pulling out the B time base knob at certain positions (two or three fastest time base settings).

[xtoffer]

Ugh, yeah that's rough. The cogwheels on mine have little red markings. Turned them all the way in one direction and they seem to line up. Had some time to reassemble and I think I managed to align the main things, bit easier than I first imagined. Not entirely sure about the thing between the coupler and the cylinder though. Only thing it can do is limit the turning somehow.. need to look up how that is supposed to work.

Really need to get this together soon, in its current state it occupies most of my precious bench space!

When the drums are fully locked counter-clockwise, the knobs (both ) also need to be at the slowest time base settting of course. The spring thingy at the back relates to the text on the front "A only' and/or "Only when knobs locked" (never could figure out which and I forgot which one I used to set it, it's not critical). It prevents pulling out the B time base knob at certain positions (two or three fastest time base settings).

Yes, the normal timebase now works fine, and the second drum turns with it.

Aah I see, as the springy thingy seems to block three maybe it should be over the "A only" (.1 .2 .5 secs)?, but I'm not sure about this functionality either. I have used it, but didn't look very close at where it was :p I tried to position it according to yours and the other pictures and it seems I didn't quite manage as it blocks 20ms, 50ms and .1s.

[rqsall]

Aah I see, as the springy thingy seems to block three maybe it should be over the "A only" (.1 .2 .5 secs)?, but I'm not sure about this functionality either. I have used it, but didn't look very close at where it was :p I tried to position it according to yours and the other pictures and it seems I didn't quite manage as it blocks 20ms, 50ms and .1s.

I just checked real quick (working at home, so...) by turning the knob and I have apparently set it in such a way that I can't pull out the B time base knob when it's at the "Only when knobs locked" positions. But no idea if it's supposed to be like that. Like you, I couldn't compare with a working version, because my B timebase was out of whack like yours.

[Andy Watson]

Just had a quick look at my 475: Never noticed before! The secondary timebase knob cannot be pulled - i.e. unlocked, on the two fastest timebase settings.

[xtoffer]

Interesting, yeah, as the 475 looks almost identical it should probably have the same functionality. Soo that would suggest the two fastest, unless that was modified as well?