Reparing old MFJ Goliath Tri-Mag mount
This is the second of these types of mounts I have had. I bought two, one with an SO-239 mount and one with a 3/8x24 mount. The 3/8x24 mount broke last year some time and was not repairable. The SO-239 mount stayed in constant service for 4-5 years... until the Thursday before Christmas. I backed out of the driveway at my dad's house and my antenna snagged a tree (all my antennas snag it) and the antenna actually broke off the mount!
What happened was the aluminum bar that the SO-239 was mounted to corroded around the connector. If you don't know what happens to aluminum when it corrodes it turns to a white powder (actually, raw aluminum is also a powder - it has to be refined and melted in to its solid metallic form we all know). Obviously, a powder doesn't have any strength at all. So, all the force of the antenna staying up was on the connector. When I snagged the tree the antenna just broke right off.
The parts/materials I used for this repair are:
1 Chassis Mount SO-239 with a 4-hole flange
4 counter-sunk 6-32 bolts (I used 1" because I couldn't find 3/4" ones at Lowes)
5 6-32 nuts (4 to lock the SO-239 down and one more as a clamp for the coax shield)
3 short hot glue sticks (for weather sealing)
spool of flux-core solder
The tools I used are:
1 reversible/variable speed drill
drill bits - 1/4", 1/2", 1/8", and 9/64" (1/16"-1/2" set had all the sizes I used)
1 stiff steel brush for the drill (or you can use a hand held steel brush if you wish)
1 hot glue gun
1 small (1/8" wide or so) flat head screwdriver
1 medium size Philips head screwdriver
1 pair small standard vice-grip locking pliers
1 45w soldering iron (other wattages would probably work)
I didn't think to get any pictures of the mount before and while I did the repair, unfortunately. I wish I did.
1. Take the old cable off by removing the cable clamp.
2. Scrape out the corroded aluminum. I used a stiff steel brush attachment for my drill to do this. When I was done there was a 1/16" dip in the aluminum bar directly under where the antenna was mounted! The bar was still solid, so I figured I would go ahead with the repair. The corrosion was just on the surface.
3. Drill out what is left of the old SO-239 (unless you can remove it completely, I couldn't) in order for the new one to fit in place. Make sure you have enough room to clear the lip on the SO-239. I used a 1/2" drill and needed to round out the hole a bit to get my connector to clear.
4. Mount the new SO-239 on the top of the bar, with the center pin going down through the bar.
5. Drill the 4 holes in the aluminum bar for the mounting bolts. I used a 1/8" drill bit to start the holes in the bar, using the SO-239's holes as a guide. This way the drill spun easy and I didn't take any material out of the bolt holes. Then I took the SO-239 off and drilled the holes. When I was done I switched to a 9/64" bit to ream out the holes in order to clear the #6 bolts.
6. Stick 3 bolts in and use the 1/4" drill to counter sink the open hole. Work your way around the flange, take one more bolt out and put it in the hole you just countersunk.
7. Put the 4th bolt in and install the nuts. Tighten them down.
Re-install the coax.
NOTE: This would be a good time to replace the coax if you need to. If you do replace the coax (which I wanted to but didn't have enough left to do it) then REPLACE WITH A HIGHER QUALITY CABLE!!!! The stock MFJ cable is JUNK. It is worse than RG-58.
8. Twist and tin the braid.
9. Wrap the braid around one of the bolts and put a nut down over top of it.
10. Solder the center conductor to the pin of the SO-239.
Now is the time for the hot glue. The hot glue is to seal the connector and coax from the elements. This is what lead to the corrosion and broken mount in the first place.
11.Put a little bit of glue around the coax where the jacket stops.
12. Re-install the coax clamp.
13. Load up the whole underneath side of the mount with hot glue. Pile on as much as you think you need - make sure you don't leave any open holes as this will be an entry point for water. Don't forget to coat the nuts and exposed bolts too.
14. Install the antenna half way on the mount.
15. Load this area up with hot glue too. Start feeding the glue in to the gap as you tighten the antenna down. Work the glue gun around the base a little bit to ensure a good seal.
16. When the antenna is tight go around the base one more time to make sure you have a good seal.
Water (and now in the winter time - salt spray) is the enemy! You have to keep out the elements in order for your system to perform and last. I should have taken the time and effort to seal up the mount when I first got it - then I wouldn't be here with the repair in the first place. So, if you are getting one of these mounts please seal it! Also, if you can or are inclined to, replace the crap coax!
0 Comments:
Post a Comment
Subscribe to Post Comments [Atom]
<< Home