Topics

Tek 465B ch 2 var broken coupler repair


jhalbrecht
 

I have a 465B that is looking good and running well, except that the coupler for ch 2 amplitude var coupler is broken.

Check these two tweets in a twitter thread for images of the broken part including an image from a USB inspection scope.
https://twitter.com/jhalbrecht/status/1353826933977485314?s=20
https://twitter.com/jhalbrecht/status/1354137517499400192?s=20

It looks like quite a lot of work to remove a board to gain access to replacing the shaft coupler - even if a new shaft coupler part exists. I don't work very _deep_ into scopes like this and don't want to put in the amount of labor / time to get in there. Looks like some connections might have to be unsoldered and/or linkages removed.

It's semi frustrating to see so many other couplers around the scope that have solid? aluminum? couplers. I assume that perhaps the coupler in question is between two different shaft sizes.

I have a lathe and could probably make a coupler, although the broken part looks a little bit like a universal joint. Some neoprene vacuum line, or vinyl fish tank airline might make a nice replacement.

I thought about gluing the broken pieces in place, but seriously doubt it would hold particularly once I tighten the set screw. A second gluing thought was to use some silicon sealer. a glob of it on the part could hit more surfaces. The broken side is closest to the pot, I wonder if I could turn it around, so gluing wouldn't be so close to the potentiometer.

All that said, I'm thinking of just gluing it with some cyanoacrylate without the broken half. It feels like sacrilege to do that to such a beautiful piece of equipment. The part could still be repaired correctly if someone wanted to tear it down in the future. There are set screws on the other end that can be undone.

If I did glue it with cyanoacrylate, I'd probably apply with a cotton swab that had it's fibers torn up so some would transfer to the repair. - Much like I've successfully repaired some parts by mixing baking soda with the cyanoacrylate.

May I be forgiven if I just glue the shaft and coupler to one another?

Comments / suggestions welcome

- Jeff


Dave Peterson
 

Jeff,
What you're describing doesn't sound terribly sacrilegious. I'm sure we've all seen far worse.
I like your take that a glue repair lends itself to a deeper repair later. I presume you personally do not use the "var" knob of channel 2 much, if ever. You're repair is likely to suffice at just holding the var shaft in the scope if you have it switched into its cal position first. Or from some means of rotating the switch at the coupler after gluing. I have my doubts about "super" glue standing up to the torque required to pass the switch detent. Not that I'm an expert. It just seems a temporary place holder, which is totally fine if that's your preference.
Let the horror stories ensue?
Dave

On Wednesday, January 27, 2021, 11:20:09 AM PST, jhalbrecht <jeffa@rodaw.com> wrote:

I have a 465B that is looking good and running well, except that the coupler for ch 2 amplitude var coupler is broken.

Check these two tweets in a twitter thread for images of the broken part including an image from a USB inspection scope.
https://twitter.com/jhalbrecht/status/1353826933977485314?s=20
https://twitter.com/jhalbrecht/status/1354137517499400192?s=20

It looks like quite a lot of work to remove a board to gain access to replacing the shaft coupler - even if a new shaft coupler part exists. I don't work very _deep_ into scopes like this and don't want to put in the amount of labor / time to get in there. Looks like some connections might have to be unsoldered and/or linkages removed.

It's semi frustrating to see so many other couplers around the scope that have solid? aluminum? couplers. I assume that perhaps the coupler in question is between two different shaft sizes.

I have a lathe and could probably make a coupler, although the broken part looks a little bit like a universal joint. Some neoprene vacuum line, or vinyl fish tank airline might make a nice replacement.

I thought about gluing the broken pieces in place, but seriously doubt it would hold particularly once I tighten the set screw. A second gluing thought was to use some silicon sealer. a glob of it on the part could hit more surfaces. The broken side is closest to the pot, I wonder if I could turn it around, so gluing wouldn't be so close to the potentiometer.

All that said, I'm thinking of just gluing it with some cyanoacrylate without the broken half. It feels like sacrilege to do that to such a beautiful piece of equipment. The part could still be repaired correctly if someone wanted to tear it down in the future. There are set screws on the other end that can be undone.

If I did glue it with cyanoacrylate, I'd probably apply with a cotton swab that had it's fibers torn up so some would transfer to the repair. - Much like I've successfully repaired some parts by mixing baking soda with the cyanoacrylate.

May I be forgiven if I just glue the shaft and coupler to one another?

Comments / suggestions welcome

- Jeff


quad@...
 

Nice! You could probably reinforce the job using a cable tie.


quad@...
 

Even better, slip on a marine grade heatshrink shroud and shrink it in place if space etc permits. else,
hold it in place using cable ties, to take the load off the glue joint.

https://www.amazon.com/Wirefy-275-Heat-Shrink-Tubing/dp/B084GWYX42


keith@...
 

If this is the flexible coupler, part number 376-0051-00, they are used in many Tektronix instruments. I had one break in a similar fashion on a SG505 oscillator. Tried to glue it and wrap it with heatshrink sleeve, but that didn't hold. The part is basically very flimsy and even a little overtightening will crack the aluminum body.

I have found a brass 0.125 inch flexible coupling made by Huco that looks like it might do the job. The manufacturer will sell direct (https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06), so I've ordered one to see if it's any good.


keith@...
 

And the coupler arrived in the post this morning. It's smaller in outside diameter that the Tek original, which is fine. The inner diameter at 0.125 inch is 2 thou smaller, which meant a few gentle strokes on the shafts with a needle file for it to fit. And fit it does nicely.


quad@...
 

The 3x3mm flexible couplings from ebay might work too with a bit more needle file work - cheaper.

https://www.ebay.com/itm/162691768380

https://www.ebay.com/itm/323891445851


Ed (SCSKITS)
 

Be careful to make sure that the flexible coupler is not being used for electrical isolation also. I find that sometimes I can use a solid coupler in place of the flexible, but if it is on a POT with high voltage on it, and the shaft to the knob is metal, I will replace the shaft with a fiberglass shaft of the same diameter. Just out of caution...

ed


jhalbrecht
 

On 1/27/2021 12:20 PM, jhalbrecht wrote:
I have a 465B that is looking good and running well, except that the coupler for ch 2 amplitude var coupler is broken.

Check these two tweets in a twitter thread for images of the broken part including an image from a USB inspection scope.
https://twitter.com/jhalbrecht/status/1353826933977485314?s=20
https://twitter.com/jhalbrecht/status/1354137517499400192?s=20
Check the above twitter thread for updated images...

Bottom line - so far - Nope :-( my JB Weld plus baking soda reinforced Cyanoacrylate not even close and certainly no cigar! :-(

I tried some _normal_ shrink wrap on the shaft, It was too easy to pull off.

I bought one of the two of two sold Tek couplers on ePay, not particularly optimist about using a used part of a poorly designed coupler.

I have some straight through couplers coming from the Robot Shop, and other source. Although the shaft is nylon providing electrical isolation there probably will be too much mechanical bind.

I think this would be a great new part, Yes I can afford $25 buck$, but I don't like it!... Check this part out. 1/8" id on both ends
https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06

Interesting McMaster-Carr page
https://www.mcmaster.com/flexible-shaft-couplings/clamping-vibration-damping-precision-flexible-shaft-couplings-11/

I have some other inquires out and will summarize if useful.

There were some great suggestions and discussion. Thank you all.
Keith suggested I could probably be forgiven if I tried glue. I didn't try... but glad for the first reply!
Quad suggested a cable time, which I hadn't thought of.., then linked to marine grade heatshrink with adhesive which I immediately bought to have on hand https://www.amazon.com/Wirefy-275-Heat-Shrink-Tubing/dp/B084GWYX42
Keith shared what I think is the proper new part to do the repair https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06 and he bought one and easily fitted it with a couple strokes of a file.
Quad shared a link to a brass traditional universal coupler https://www.ebay.com/itm/162691768380 I ordered a couple.
Jeff Dutky shared the now zero stock Tek part on ePay
Ed warned to be sure of electrical isolation. The shaft on my 465b is nylon
Eric suggested a part on Amazon, I couldn't find a 1/8" version. I'm pretty surprised I couldn't find it on Amazon, they had a lot of couplers..

O.K. the project is on hold until a few of these parts come in. Thanks again for the comments and suggestions.

  - Jeff


--
Jeff Albrecht KF7CRU @jhalbrecht


Michael W. Lynch
 

Jeff,

I believe I have what you need here. Contact me off list. I will send a picture and we can discuss getting this to you. I have two types of the original TEK 1/8" coupler. the solid and the one with the "flex" joint. Solid is used on the Position controls and flex is used on the VAR Controls. You pay postage and you can have either one.

mlynch002atgmaildotcom or mlynch003atyahoodotcom

Thanks!

--
Michael Lynch
Dardanelle, AR


jhalbrecht
 

Hi All,

I've completed the repair of the Ch. 2 VAR coupler.

Cyanoacrylate  glue up didn't work, coupler broke again in the same spot surprisingly quickly.

I ordered a couple straight through couplers from The Robot Shop and ePay but they still haven't arrived, I became impatient and continued the repairs with what I had received.

I wanted to try some automotive vacuum tube, but found it too difficult to get it placed as I wanted to accomplish the repair without removing PCBs. I did loosen one PCB that gave me enough clearance to get the old part out and install the replacement.

Big thanks to Michael!
who sent me 1/3 of the coupler that matched up to the two thirds of mine that were undamaged. I had been apprehensive about replacing the coupler with the same part thinking it would probably fail as mine had. But I'm thinking someone just tightened that one too much, because with a gentle snug of the set screws the replacement coupler felt strong and functions fine.

Thanks everybody.

  - Jeff

On 1/30/2021 10:10 AM, jhalbrecht wrote:
On 1/27/2021 12:20 PM, jhalbrecht wrote:
I have a 465B that is looking good and running well, except that the coupler for ch 2 amplitude var coupler is broken.

Check these two tweets in a twitter thread for images of the broken part including an image from a USB inspection scope.
https://twitter.com/jhalbrecht/status/1353826933977485314?s=20
https://twitter.com/jhalbrecht/status/1354137517499400192?s=20
Check the above twitter thread for updated images...

Bottom line - so far - Nope :-( my JB Weld plus baking soda reinforced Cyanoacrylate not even close and certainly no cigar! :-(

I tried some _normal_ shrink wrap on the shaft, It was too easy to pull off.

I bought one of the two of two sold Tek couplers on ePay, not particularly optimist about using a used part of a poorly designed coupler.

I have some straight through couplers coming from the Robot Shop, and other source. Although the shaft is nylon providing electrical isolation there probably will be too much mechanical bind.

I think this would be a great new part, Yes I can afford $25 buck$, but I don't like it!... Check this part out. 1/8" id on both ends
https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06

Interesting McMaster-Carr page
https://www.mcmaster.com/flexible-shaft-couplings/clamping-vibration-damping-precision-flexible-shaft-couplings-11/

I have some other inquires out and will summarize if useful.

There were some great suggestions and discussion. Thank you all.
Keith suggested I could probably be forgiven if I tried glue. I didn't try... but glad for the first reply!
Quad suggested a cable time, which I hadn't thought of.., then linked to marine grade heatshrink with adhesive which I immediately bought to have on hand https://www.amazon.com/Wirefy-275-Heat-Shrink-Tubing/dp/B084GWYX42
Keith shared what I think is the proper new part to do the repair https://www.huco.com/shop/couplings/oldham-coupling-1/oldham-coupling-2/500-06 and he bought one and easily fitted it with a couple strokes of a file.
Quad shared a link to a brass traditional universal coupler https://www.ebay.com/itm/162691768380 I ordered a couple.
Jeff Dutky shared the now zero stock Tek part on ePay
Ed warned to be sure of electrical isolation. The shaft on my 465b is nylon
Eric suggested a part on Amazon, I couldn't find a 1/8" version. I'm pretty surprised I couldn't find it on Amazon, they had a lot of couplers..

O.K. the project is on hold until a few of these parts come in. Thanks again for the comments and suggestions.

  - Jeff

--
Jeff Albrecht KF7CRU @jhalbrecht