A different way to make Tek TM500/5000 plug-ins


With the discussion of TM500 test plug-ins, I thought it was worthwhile to mention a different approach that is easily implemented to make the mechanical housings, since usable scrap TM500 plug-ins are hard to find these days.. Some years ago I looked at this problem, and realized that a common technique used in the avionics control world would work perfectly for this task, boxes made from tapped square stand-offs.

RAF Hardware makes square cross-section female stand-offs of any length.
you can see them here, and down load the catalog (ignore the picture of the hex parts):

The square ones are not obvious on the site, but they exist,and are incredibly handy for making enclosures. and I got many long samples to experiment with, and made a mock-up of the TM500 case easily. I will see if I can track ti down to provide pics. I( can't remember now if I used 3/16" or 1/4" parts.

To use them to make a housing, it requires 6 pieces, three at the top, with the left hand ones close together to form the narrow top slo fro the frame guide tab, and three at the bottom with the left ones farther apart to bracket the black plug in plastic guide at the bottom of the frame. The faceplate was solid aluminum, with six counter-sunk holes to attach the 6 stand-offs, and the rear is also a similar plate, with a cutout for the card to pass through. It (the rear panel) could be easily made from a PCB, making the slots and holes much easier to fabricate, and quite inexpensive. In this way, little fabrication skill is required, as the front is just a simple sheared plate, as are the sides (in thin material), and the rear is a fabbbed PCB. Interior boards are easily attached to the square stand-offs with tapped holes (with small internal stand-offs to get the riight exact spacing for the mating pcb connector in the frame). Needless to say, a double wide plug-in is just wider, but still needs at least the extra bottom slot stand-offs for alignment. The open top and bottom dramatically improves air circulation and heat removal over the stock box.

The side covers (if needed) can just be flat sheets with 4 countersunk holes, to be screwed to the outside square stand-offs into tapped holes. I did not find the lock essential at all, and I added a small pull handle to the front instead to more easily remove the plug-in, as this is especially relevant for the frame tester unit which is constantly removed and inserted. The lock is just a nuisance in that application. This structure is much more solid that the usual TM500 case due to the rear panel and rigidly attached sides.

Anyway, just passing along my previous escapades in this area, and I should point out that this method really lends itself to local assembly and low cost. If I can track down my original prototype, I will post some pics and details. It's all stuffed away in a box somewhere.

all the best,
walter (walter2 -at-
sphere research corp.