Topics

Horizontal Display switch shenanigans.


Dave Peterson
 

While pulling apart this 465 parts scope I tried removing the pushrods from the Horizontal Display switch on the A7 board. Working on the bottom "B DLY'D" pushrod the push button came out of the switch. I thought at first that it must be a simple mechanical assembly thing that I could put back together. When I had the chance to study it I realized that the plastic of the button had broken. I thought I must have done it trying to take the pushrod off, but then I noticed that the internal plastic button narrows to a very small "T" cross section. See the pictures in:

https://groups.io/g/TekScopes/album?id=257214

Notice the dirtiness of the cross section at the break. If the button was intact before I tried taking the pushrod off it must have been just by the top of the "T" and taken very little force to break it. I suspect it was already broken actually, and that having the board out of the scope allowed the pushrod to rotate down so that the button could come out of the switch assembly. When held horizontal the notches in the button catch on the ratchet mechanism of the switch, holding it in. When it rotated down it just came out with no force, nor did it make any noise. It just kind of fell out in my hand.

The back of the plastic internal button when complete has two channels that hold the metal spring contacts, which slide between the switch posts. I don't know if that's clear in the pictures or not. The point being, if this back piece with the contacts breaks off it ends up inevitably in the back of the switch. In the depressed position. I never turned this scope on - it wouldn't have worked with C1419 shorted anyway. I also didn't capture the back of the switch in any pictures nor notice if the button was visible from the back. They are when in the depressed position. So it's kind of lucky that I found this. If I'd tried the scope it would probably would be stuck in B DLY'D, or something worse with B DLY'D selected and whichever of the other buttons in the HORIZ DISPLAY group would be depressed. It's a pretty devious failure mode, and I have to wonder how common it is, given the fragility of that cross section.

Anyone else with experience with this kind of pushbutton failure?

But wait, there's more!

After finding this broken switch I looked it up by the Tektronix part number from the service manual I have - Fig 2 Circuit Boards, item 124: 260-1423-00, "SWITCH, pushbutton--HORIZ DISPLAY". I found a NOS listing from a company called "Talon Electronics LLC". I ordered it, but was surprised to find on my order after a day some notes from someone in the shipping department which read "cut pin", and submitted a refund for me. But then also shipped it anyway noting "might work in his application". Aw! How nice of them!

So the part came the other day. I unpacked it and compared to my A7/switch. Look at the last two pictures in the above album. Sure enough there's a "cut" pin, but note there's also a cut pin on the existing B DLY'D switch. But look closer: the new part has the wrong pin cut! The new switch in the picture is "on its back". It would be flipped over putting the cut pin at the front side of the board, not the back! Ahg! At least I got a refund. How the heck did this NOS part get in the system in the first place!? Bo-bo in the manufacturing process? Someone had too much to drink the night before and cut a whole batch of switches with the wrong leg cut?

So now what? I'm thinking what I'll do is cut the rearward pin of the new B DLY'd switch, and then cut the existing switch forward pin leaving it soldered into the board. Then when I mount the new switch I'll solder the new switch cut pin to the existing post from the old switch? Maybe place a piece of lead along the post and solder that?

Any other ideas or suggestions for this? I do see another one on eBay, but used. So no assurance that it's in good working order.

But what a convoluted situation! I wanted to share the failure of the switch. It seems like a hidden failure that someone might benefit from the experience. I'd also love to hear any ideas for "fixing" the new switch. Or should I just buy the used one on eBay?

Dave


adesilva_1999@...
 

Hi Dave,
Check this: https://www.mouser.com/ProductDetail/TE-Connectivity/510-AG90D-10?qs=%2Fha2pyFaduhM4gHyZk8iA5%252BbCzoO6EXmbo0JD0Y5IKbJxRi4JyNZJA%3D%3D

You can get something like this and break off just one pin and solder in place. Depending on the diameter of the pin on the switch, It might mate with the open end. If you need to test it out, I can send a couple of the to you.

One other method is to wrap around a similar diameter copper wire (single strand) and solder it close to the bottom of the switch leg. and slightly bend it to go in the PCB hole. I will PM you if you want to talk.

Ananda


Dave Peterson
 

Ooo. Thanks for that! Not only does that make for a viable solution, I've been wondering about a suggestion from an EEVBlog thread in which someone replaced soldered wire connections with connectors. These would work for that too perhaps. The bigger lead here is thinking about going Mouser for such construction solutions. I'm learning.

Thanks for the tip!Dave

On Friday, November 27, 2020, 11:00:39 PM PST, adesilva_1999 via groups.io <adesilva_1999=yahoo.com@groups.io> wrote:

Hi Dave,
Check this: https://www.mouser.com/ProductDetail/TE-Connectivity/510-AG90D-10?qs=%2Fha2pyFaduhM4gHyZk8iA5%252BbCzoO6EXmbo0JD0Y5IKbJxRi4JyNZJA%3D%3D

You can get something like this and break off just one pin and solder in place. Depending on the diameter of the pin on the switch, It might mate with the open end. If you need to test it out, I can send a couple of the to you.

One other method is to wrap around a similar diameter copper wire (single strand) and solder it close to the bottom of the switch leg. and slightly bend it to go in the PCB hole. I will PM you if you want to talk.

Ananda


adesilva_1999@...
 

Now that you have it out of the board, what is the size of the pin? Like I said, I can send a couple of them in the mail.


Dave Peterson
 

I don't have it out of the board yet, but I could measure the new one. They're thick - like 2mm? I'd have to measure, and I'm shutting down for the day. Thanks for the offer. I'll look at it tomorrow.
Dave


 

On Sat, Nov 28, 2020 at 07:01 AM, Dave Peterson wrote:


Any other ideas or suggestions for this?
With these "radio button" sets, it's often possible to just replace one stem, without much disassembly nor removal of the set. You'd need to move the interlocking-bar and spring out of the way first though.

Raymond


Dave Peterson
 

Thanks Raymond. I was wondering about that.

Do you just pull the lead out of the switch with some pliers? I imagine one needs to be careful about the switch position, or the switch contacts re-inserting? I figured I'd give this a try when I have the old one out. Not try it on the new on.

Parts are arriving, so busy on many fronts!
Dave


Renée
 

I have actually completely disassembled and swapped bits and pieces of switches ( and other mechanical items) when unable to find what I want. the only time I could not effect a repair is when the assembly is molded . and at that although there are times that is even possible depending on how inventive and how much time ya wants to spend. you have very little to loose if it is already broke, take your time being careful is the motto....if it was mechanically assembled it can be re-worked. If man made it....
Renée

On 11/27/20 10:01 PM, Dave Peterson via groups.io wrote:
While pulling apart this 465 parts scope I tried removing the pushrods from the Horizontal Display switch on the A7 board. Working on the bottom "B DLY'D" pushrod the push button came out of the switch. I thought at first that it must be a simple mechanical assembly thing that I could put back together. When I had the chance to study it I realized that the plastic of the button had broken. I thought I must have done it trying to take the pushrod off, but then I noticed that the internal plastic button narrows to a very small "T" cross section. See the pictures in:

https://groups.io/g/TekScopes/album?id=257214

Notice the dirtiness of the cross section at the break. If the button was intact before I tried taking the pushrod off it must have been just by the top of the "T" and taken very little force to break it. I suspect it was already broken actually, and that having the board out of the scope allowed the pushrod to rotate down so that the button could come out of the switch assembly. When held horizontal the notches in the button catch on the ratchet mechanism of the switch, holding it in. When it rotated down it just came out with no force, nor did it make any noise. It just kind of fell out in my hand.

The back of the plastic internal button when complete has two channels that hold the metal spring contacts, which slide between the switch posts. I don't know if that's clear in the pictures or not. The point being, if this back piece with the contacts breaks off it ends up inevitably in the back of the switch. In the depressed position. I never turned this scope on - it wouldn't have worked with C1419 shorted anyway. I also didn't capture the back of the switch in any pictures nor notice if the button was visible from the back. They are when in the depressed position. So it's kind of lucky that I found this. If I'd tried the scope it would probably would be stuck in B DLY'D, or something worse with B DLY'D selected and whichever of the other buttons in the HORIZ DISPLAY group would be depressed. It's a pretty devious failure mode, and I have to wonder how common it is, given the fragility of that cross section.

Anyone else with experience with this kind of pushbutton failure?

But wait, there's more!

After finding this broken switch I looked it up by the Tektronix part number from the service manual I have - Fig 2 Circuit Boards, item 124: 260-1423-00, "SWITCH, pushbutton--HORIZ DISPLAY". I found a NOS listing from a company called "Talon Electronics LLC". I ordered it, but was surprised to find on my order after a day some notes from someone in the shipping department which read "cut pin", and submitted a refund for me. But then also shipped it anyway noting "might work in his application". Aw! How nice of them!

So the part came the other day. I unpacked it and compared to my A7/switch. Look at the last two pictures in the above album. Sure enough there's a "cut" pin, but note there's also a cut pin on the existing B DLY'D switch. But look closer: the new part has the wrong pin cut! The new switch in the picture is "on its back". It would be flipped over putting the cut pin at the front side of the board, not the back! Ahg! At least I got a refund. How the heck did this NOS part get in the system in the first place!? Bo-bo in the manufacturing process? Someone had too much to drink the night before and cut a whole batch of switches with the wrong leg cut?

So now what? I'm thinking what I'll do is cut the rearward pin of the new B DLY'd switch, and then cut the existing switch forward pin leaving it soldered into the board. Then when I mount the new switch I'll solder the new switch cut pin to the existing post from the old switch? Maybe place a piece of lead along the post and solder that?

Any other ideas or suggestions for this? I do see another one on eBay, but used. So no assurance that it's in good working order.

But what a convoluted situation! I wanted to share the failure of the switch. It seems like a hidden failure that someone might benefit from the experience. I'd also love to hear any ideas for "fixing" the new switch. Or should I just buy the used one on eBay?

Dave




Dave Peterson
 

It was late, my brain wasn't firing on all cylinders. 2mm? Really Dave? They seemed thicker than 1mm, but I just went and measured: 1mm. So there ya go, exactly 1mm.

How have you guys removed this assembly? Solder wick? Heat gun? The board seems a robust big component kind of thing that a heat gun would work on. No surface mount Rs & Cs to float off. I've never actually done a hot air dismount before, so any ideas/suggestions are appreciated.

Dave


 

On Sat, Nov 28, 2020 at 06:15 PM, Dave Peterson wrote:


Do you just pull the lead out of the switch with some pliers?
If that relates to my earlier message, I don't understand. If it doesn't and you thought about pulling a switch contact pin out of the body of the switch and out of the PCB: don't, AFAIK, it's an insert-once construction. I'd be interested to know whether it actually is though...
I suggested moving the bar or clip holding the movable stem out of the way, after which the plastic stem (the part that is broken in your assembly) may come out easily. I've done that several times, not sure about this particular model.

Raymond


adesilva_1999@...
 

1 mm sounds close. I thought as much. As for removing it, the best is to use a de-soldering gun since it is a double sided board. Solder wick might work but it will depend on the size of the hole vs. the pin diameter. Can't risk the damage to the plate-through.
Ananda


Dave Peterson
 

This is why I think things 3 and more times over before I proceed. And still I sometimes miss the obvious. Some people call me smart, but I know how often I miss such obviously simple solutions. KISS. Duh.

Yes, I've got you now Raymond: replace the broken pushbutton, not the whole damn switch assembly. No soldering required.

Gads, I get annoyed with myself when I get so block-headed.
Dave


Dave Peterson
 

So here I am at the bench again getting ready to reassemble the CH1 attenuator input Rs & Cs. I'm going to clean up the connections to the A3 board and would like to remove the Vertical Mode pushbuttons/pushrods to protect them from being damaged by an errant soldering iron.

I don't like my method of pulling these things off. I'm pulling away longitudinally on the pushrod while twisting a screw driver between the pushrod connection to the switch - to open the end enough to release.

The screwdriver keeps marring the pushrod, and any direct lateral prying at the pushrod end puts a lot of force on the switch pushbutton. And as noted earlier, these buttons are pretty fragile as it is.

How do you guys remove these? Is the above pretty much it, and such "damage from repair" part of the process?

Dave


adesilva_1999@...
 

Are you trying to avoid damaging the push rods on the vertical board while removing that braided thingy? I would simply cut it off. Once the board is out, you can solder a new and longer piece of braid. You can then bring it under the push rods and solder it a little away from them.


Dave Peterson
 

In this case I was removing the Vert Mode pushrods to avoid damage to them during some clean up. And just handling in general.

But as it take them off I feel I'm being rather brutal, so just curious what more experienced folks do. Taping into the community experience base.

I'm getting better at it, getting the hand-eye coordination and feel of it. Screwdrivers still feel a little brutish, and are leaving little marks on the pushrod. Nothing too gross, but still I prefer methods that don't leave behind evidence of man-handling.

Dave


 

On Sat, Nov 28, 2020 at 10:37 PM, Dave Peterson wrote:


I'm getting better at it, getting the hand-eye coordination and feel of it.
Screwdrivers still feel a little brutish, and are leaving little marks on the
pushrod. Nothing too gross, but still I prefer methods that don't leave behind
evidence of man-handling.
I use the "cutting" edge of a blunt knife (as I do in most cases where a screwdriver is recommended). I hold that in the slit of the "female" push rod side (knife almost parallel to the push rods) and move it carefully (rotate it away from lengthwise), so it widens one of the open ends slightly. While pulling slightly, I tilt the male side push rod then slightly, so it "steps on or over" the interlocking protrusion. While pulling, so it won't snap back, I reorient the knife so it pushes against the other side of the "female" part. A little wiggling and the male part comes out.
Does that make sense?
It helps when heated to about 30 - 40 Centigrade.

Raymond


Dave Peterson
 

Hmm, yes, I know what you're describing. I was trying this method with small screwdriver tips but felt I was applying to much lateral force to the switch pushbutton. I'm really scared of those things now, seeing that tiny cross section. And I wasn't having success keeping the one side off while going at the other.

I like the, shall we say warmth, idea. One pushrod I feel like I plastically deformed it (materials science class: plastic vs. elastic deformation) opening it it. Part of the brutishness I'm trying to avoid. So I think a little heat might help. I'm sitting in an unheated garage in San Francisco, so warm isn't a word I'd use to describe the working environment. Ha-ha.

Thanks for the tips.
Dave


 

On Sat, Nov 28, 2020 at 11:22 PM, Dave Peterson wrote:


I know what you're describing. I was trying this method with small screwdriver
tips but felt I was applying to much lateral force to the switch pushbutton.
I'm really scared of those things now, seeing that tiny cross section.
I think your switch might well have been damaged already. Normally, very little force is exerted laterally during this procedure. I've taken apart and re-assembled lots of 'scopes and (7000-series) plugins having the same construction and (AFAIR) never had any breakage of any these parts.
I especially think using a small screwdriver, as is usually advised, is a bad idea, because of lack of control and greater damage to the slit. The longer lever base in the slit as well as because of the longer length of the knife applied in parallel, causes less damage and allows for better control and less pressure on the parts.
BTW, I'm using the cutting edge of a non-serrated, very blunt breakfast knife.

Give it a thought, try it out and do it your preferred way!

Raymond


Dave Peterson
 

See the photos in https://groups.io/g/TekScopes/album?id=257214.

Something's finally fixed!

Thanks for the suggestion Raymond.
Dave


 

Well done, Dave. Did you exchange the one switch? Or even just the broken plastic part? Can't see.

Raymond