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Tektronix 577-177 test jig measurements.


Jared Cabot
 

Hi all!
New member here, just looking for a little help.
I recently picked up an old Tektronix 577-177 curve tracer that needs some restoration and repair and I though I'd give making some test jigs of my own a go as well.

Does anyone have measurements of the test sockets in the 177 test jig? I read somewhere that they were provided in one of the manuals or similar, but I haven't been able to find anything.

Thanks!


 

Hi Jared,

It is really simple. Banana plugs and sockets are ALWAYS 3/4" apart on all instruments. So the three banana plugs in a row are 0.75" apart for a total of 1.5".
The Kelvin contacts are shifted 0.5" horizontally and those two contacts are also 0.75" apart. You can see they are spaced midway between the three EBC contacts.

Dennis Tillman W7PF

-----Original Message-----
From: Jared Cabot
Sent: Wednesday, February 13, 2019 5:52 AM

Hi all!
New member here, just looking for a little help.
I recently picked up an old Tektronix 577-177 curve tracer that needs some
restoration and repair and I though I'd give making some test jigs of my own
a go as well.

Does anyone have measurements of the test sockets in the 177 test jig? I read
somewhere that they were provided in one of the manuals or similar, but I
haven't been able to find anything.

Thanks!



--
Dennis Tillman W7PF
TekScopes Moderator


bobkrassa
 

Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL


Glydeck
 

Jared,

I posted a detailed PDF of the 577 / 576 spacing, including the safety switch probe.

Here at TekScopes-groups.io
https://groups.io/g/TekScopes/files/576_577TestFixture.pdf

Added to page 32 of the PDF Manual on TekWiki - w140.com
http://w140.com/Tek_177_service.pdf

Hope this helps,

George

On Feb 13, 2019, at 10:16 AM, bobkrassa <bob@krassa.com> wrote:

Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL



tom jobe <tomjobe@...>
 

Hi Bob,
I checked the two 575's I have and they fit the later style test fixtures that have the Kelvin connectors quite well. I also checked the with some 'Pomona' brand dual banana plugs so that I was only testing two banana plug sockets at a time, and again all seemed well.
Measuring the center to center spacing of the banana plugs on multiple test fixtures showed them to have a range of center to center dimensions of about 0.745 to 0.755 inches or  18.92 mm to 19.18 mm.
The nature of banana plug hardware seems to be very forgiving of small errors in the center to center spacing.
tom jobe...

On 2/13/2019 10:16 AM, bobkrassa wrote:
Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL


tom jobe <tomjobe@...>
 

After further thought, I remembered that I had a box with many bits and pieces left over from repairing quite a few broken Tektronix test fixtures years ago.
In the box were sketches of the various parts I had made complete with dimensions, which brought back some of this from memory.
The banana pins on the back of the original Tek test fixtures get centered by the threaded part of the screw that fastens them into the test fixture body, and in the extreme case I measured today, the screw diameter over the threads is 0.020" smaller than the largest hole in the test fixture bodies I measured, so the center to center dimension of any two banana pins can easily be off of the nominal 0.750 center to center dimension by 0.020" or 0.5 mm, which is not good.
Obviously I had seen this problem before, because I had accurately made the five hole pattern in a piece of 1/2" thick steel plate with the holes slightly smaller than the original test socket holes, and used that as an assembly jig for the test fixtures. With the five pins slightly loose in the test fixture body, the test fixture was plugged into the steel piece and had the banana pin screws tightened to get them close to the nominal spacings. You could do the same thing by loosening the pins a little and plugging the test fixture into your curve tracer before gently re-tightening the screws in a gradual fashion like it was a cylinder head on an engine.
On the small Kelvin test fixtures there are four small #2-56 threaded screws that come from the backside that hold the top cover plate on. Be careful about how much re-tighten these screws on re-assembly as the threaded boss will break off of the backside of the test fixture cover plate very easily... as you probably know all too well if you have worked on these test fixtures.
I had several used test fixtures I had bought with these threaded bosses pulled off of the cover plates, so I made some threaded brass pieces that had a head on them like a nail. They dropped through the holes I drilled in the original cover plate corners and were secured with epoxy on assembly. This arrangement used the original style of tiny #2-56 screw fastening from the underside of the test fixture.
If anyone is interested in any of this, I will provide some dimensions and photos of whatever you want to see, but only directly to the person who requests it. If you want to share this information or think it needs to be posted elsewhere, you can do that.
tom jobe...

On 2/13/2019 1:23 PM, tom jobe via Groups.Io wrote:
Hi Bob,
I checked the two 575's I have and they fit the later style test fixtures that have the Kelvin connectors quite well. I also checked the with some 'Pomona' brand dual banana plugs so that I was only testing two banana plug sockets at a time, and again all seemed well.
Measuring the center to center spacing of the banana plugs on multiple test fixtures showed them to have a range of center to center dimensions of about 0.745 to 0.755 inches or  18.92 mm to 19.18 mm.
The nature of banana plug hardware seems to be very forgiving of small errors in the center to center spacing.
tom jobe...




On 2/13/2019 10:16 AM, bobkrassa wrote:
Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion.  Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL




Jared Cabot
 

Hi,

Yep, I got that 3/4" (19.01mm in metric land) no worries.
The other measurements make sense too, I just gotta remember to recalibrate myself in inches when working on this stuff. :D

That drawing that Glydeck posted looks to be exactly what I need. I'll compare it to the drawing I made and see how far off I was....

Tom, if you could email me some of those photos, that would be great. I always like seeing different ways of doing stuff so I can get new ideas or see things I didn't think of. :)
I plan to make some of my own adapters with stacked PCB's spaced by brass standoffs to make a kind of sandwich. Standard base with banana jacks on ground floor, 1st floor will be the specific layout to the test socket in question and second floor will have cutouts and mounting holes for mechanical support of the test sockets and also labels etc.