Topics

Switch retainers for 7000 series plug ins

Martin Whybrow
 

I've just acquired a 7854 scope for a nice price; the 7B15 timebase module that was included has a pushed-in switch (S90) which I have found to be due to a broken plastic catch that should be holding the switch onto the PCB. Is there a source for these, other than from a scrap plug in?

Clark Foley
 

I had a similar problem on an early 7k prototype mainframe Vert Mode Select switch. I could not find loose replacement parts.

*******WARNING**********
Collectors and instrument restorers should not read further as I do not wish to offend!
*******WARNING**********

I drilled two small holes through the PCB and strung some no.24 (AWG) steel wire through the holes and looped the wire over the tail of the switch where the nylon clip grabbed the body. Twist the wire together on the back side of the PCB. Crude but effective. Of course you need to avoid traces. I would not have the heart to do this to an otherwise unsuspecting and pristine PCB.

I warned you!

Dave Trainor
 

I have a couple of parts TM500 plugins, one a FG400 (witch was sorta
diagonally crushed in shipping) (very sad). It has pushbutton switches,
does anyone know if the pushbuttons are the same? If so I may have 3 or 4
that are not damaged. But I donĀ¹t know not having a 7000 series plugin if
they are even close to the same.

73- Dave N8ZFM

On 2/4/20, 11:16 PM, "TekScopes@groups.io on behalf of Clark Foley"
<TekScopes@groups.io on behalf of clarkfoley@...> wrote:

I had a similar problem on an early 7k prototype mainframe Vert Mode
Select switch. I could not find loose replacement parts.

*******WARNING**********
Collectors and instrument restorers should not read further as I do not
wish to offend!
*******WARNING**********

I drilled two small holes through the PCB and strung some no.24 (AWG)
steel wire through the holes and looped the wire over the tail of the
switch where the nylon clip grabbed the body. Twist the wire together on
the back side of the PCB. Crude but effective. Of course you need to
avoid traces. I would not have the heart to do this to an otherwise
unsuspecting and pristine PCB.

I warned you!




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Hi Martin,
That sounds like the Source INT/LINE/EXT pushbutton switch.
If I am correct it uses three modular 2-piece switches. Those are fragile and have several different failure mechanisms.
There is a Pushbutton Switch repair guide on TekWiki. I believe it discusses how to fix them if you have the parts. That is a big IF.
http://w140.com/tekwiki/images/2/24/Repairing_tek-made_board-mounted_push-button_switches.pdf

I know from experience how to fix them because I have had many of them break.
Each time I first have to find a donor plugin which gets harder and harder.

Good luck,
Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Martin Whybrow
Sent: Tuesday, February 04, 2020 2:49 PM
To: TekScopes@groups.io
Subject: [TekScopes] Switch retainers for 7000 series plug ins

I've just acquired a 7854 scope for a nice price; the 7B15 timebase module that was included has a pushed-in switch (S90) which I have found to be due to a broken plastic catch that should be holding the switch onto the PCB. Is there a source for these, other than from a scrap plug in?





--
Dennis Tillman W7PF
TekScopes Moderator

Martin Whybrow
 

Actually it's the single gang switch that selects 1MOhm or 50Ohm impedance on the external trigger. The switch itself is fine, it's the grey plastic latch that retains it to the PCB that's damaged.

Martin Whybrow
 

Dave, I can't locate any information on the FG400; can you point me in the right direction please?

Dave Trainor
 

Sorry, auto-correct must have fixed that for me. I meant FG 504. And
from what I am hearing its a different type of switch, however I have a
set of the FG 504 switches. My apologies for sending it as FG400.

Thanks,
Dave N8ZFM

On 2/5/20, 5:23 PM, "TekScopes@groups.io on behalf of Martin Whybrow"
<TekScopes@groups.io on behalf of martin@...> wrote:

Dave, I can't locate any information on the FG400; can you point me in
the right direction please?




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Martin Whybrow
 

Yes, the switches in the FG504 are not the same type unfortunately.

 

Hi Martin,

The switch you need is going to be extremely hard to find for several reasons:
* Tek started using these switches late in the lifetime of the 7000 series. So they are not very common.
* The switch holder is riveted to the PC board so it is unlikely that this part would be saved.
* The sliding contacts on the removable part are extremely tiny and they fall out when you remove that part of the switch so those will get lost unless you are very careful to save them too.

For those reasons I think it is extremely unlikely that you will find what you need. Instead you need to consider an alternative to save that valuable plugin:
* Live with it the way it is. I rarely use the External Trigger input. Any signal requiring an external input trigger to a 7B10/7B15 is going to be able to drive 50 ohms. So the smart thing to do would be to hard wire this switch to the 50 ohm input impedance on the PC board. If you ever need 1Meg impedance use the 7B10 as your External Trigger instead.
* Clark Foley's suggestion to put a piece of wire through the rivet hole is a good one except in this case it might be difficult because of where the rivet holes are located.
* A piece of busbar or stiff wire about 0.050" in diameter might work to secure the switch holder to the PC Board if it is a tight fit in the hole and can be wedged into it.
* Careful application of some epoxy may also work.
* I have some tiny Philips head self-tapping screws (0.060" dia.) which might fit provided you had a Philips screwdriver that had a PH00 tip. It might require some patience to get them in the hole on the switch holder and then into the hole on the PC board. These self-tapping screws have the advantage that they can be inserted from the component side of the PC board without removing the PC Board and if they work you are done.
*If you can get the rivet out entirely then there are more options such as slightly larger machine screws with nuts for 0.085" holes. I have those too. You would need to get to the other side of the PC board to put the nuts on.

I can send you two of both the machine screws and nuts and the self-tapping screws.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Martin Whybrow
Sent: Thursday, February 06, 2020 10:53 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Switch retainers for 7000 series plug ins

Yes, the switches in the FG504 are not the same type unfortunately.





--
Dennis Tillman W7PF
TekScopes Moderator

Martin Whybrow
 

I've just returned to this, I have managed to secure the front of the switch using a tiny self tapper, but this doesn't work at the back because the actuating shaft of the switch protrudes too far and hits the screw. It looks like I need to fabricate something along the lines of what Clark suggested.