[Asterisk-Users] Re: Boards falling out...

[Stephen R. Besch]

Greg Kedrovsky wrote:

> I have a TDM40B, 4-port fxs card. Each port seems to have it's own
> little board on the fxs card. Each little board is not sodered in, but
> rather "hangs" (I have a vertical case for the server) on what I would
> call jumper pins (sorry, I'm not a profession geek, just a wannabe). One
> of my little boards, over time, slides off those jumper pins. I just
> noticed it this morning. I had to power down, seat it, and power up
> again. That's a pain. 
> 
> We did, though, have an earthquake this morning. That may have shaken
> things loose a bit. But, it wasn't much to speak of (long, but not
> strong). 
> 
> Has anyone else experienced this problem? What could I do to solve it
> (seat the little card a little more permanently)? 
> 
> Thanks ahead of time.
> 
> -Greg
> 
There are three issues here, relating to the other posts on this topic. 
   Don't use loktite. Loktite is what is called an anerobic adhesive. 
Specifically, it is catalyzed by contact with metal in the absence of 
oxygen. As such, it will only cure (in the absence of some other 
chemical activator) only down inside the pin sockets, holding them 
together. The rest will stay uncured and spread all over other stuff. 
This may essentially make them a single use contact.

The silicone is a good bet.  The acid referred to is the acetic acid 
(i.e., vinegar) released when the monomers in the RTV goo cross react to 
form the silicone. Once the cure is complete, there is no acid 
production and what was produced diffuses away. Mild acids are not 
terribly corrosive to most metals, and not at all corrosive to gold. 
The types of RTV that don't produce acid may actually produce alkali 
(ammonia), which is far more corrosive, but also diffuses away readily. 
Nevertheless, I would stick to the stuff that smells like vinegar.

Finally, I have found that the best approach is the simplest, when it 
works. If you can get one of those nylon tie-wraps around the daughter 
card in such a way as to hold it in place, this is the best - and most 
reversible approach. Sometimes, there are appropriate holes in the 
motherboard, othertimes the ty-wrap can be snaked around under the 
connector - however, don't run it under any other type of component.  I 
have even drilled holes in 2-layer circuit boards, but I would not 
advise this unless you really, really, really know what you are doing.

Finally, if the female side of pin sockets are loose enough to let the 
dayghter cards fall out, they may also be the source of noisy, 
intermittent connections.  Sockets of allmost all kinds are notorious 
for this kind of thing. I can't tell you how many times I have repaired 
a flakey circuit board by removing the sockets and soldering in all the 
(formerly) socketed chips. The square pin spring contacts in those 
connectors are only designed for a few insertion/removal cycles.  If 
that is the case, you should get a good repair tech. to replace them.

Good luck and hang in there.

Stephen R. Besch