[time-nuts] MTI 260-0624-D OCXO

[Rex]

About opening cases, I opened one, repaired the oscillator and sealed it 
back up (sort of).

In the early 2000's I had a 10 MHz OCXO that I used as the main 
reference for my 10 GHz ham rover rig. It was really doing the job for 
me until I accidentally hooked it up to DC power backwards and killed 
it. I was hoping I could find some way to fix it. The oscillator was one 
of the larger metal packages about 3" long by about 2" square. Here's 
how I opened it.

Earlier I had tried to unsolder a smaller oscillator (about the size of 
the MTI 260) with a torch. It's hard to heat the two sections fast with 
a torch to melt the solder and find a way to grab them both ad pull 
apart while the solder is melted. On that attempt, I eventually got it 
apart but desoldered some internal circuit board components in the process.

For this other broken oscillator that I liked, I decided it might be 
better to mechanically cut it apart. I assumed that the bottom piece 
probably had a lip about 1/4 to 3/8 " long that fit tightly inside of 
the top case and that lip was soldered to join the two pieces. I wanted 
to cut off the top case right where the solder joint ended. I first 
drilled a small test hole into the side of the outer case about where I 
guessed the solder joint ended inside, Ideally just through the outer 
case. Then with a small Dremel bit I enlarged this hole to to figure out 
exactly where the solder seam ended. Then I carefully cut the main case 
around the end of the solder joint. Ideally I cut just a little below 
the end of the inner lip to keep a slight aligning surface for putting 
it back together later.

For the cutting, I had a milling machine that I used, But once you know 
where you want to cut, I think careful hack sawing or a Dremel ceramic 
disk could have done the job. With only a little bit of solder now 
holding the cut top case on, a little prying removed it.

[Another option might be to cut vertical slits in the outer case just 
either side of the round corners (8 cuts) and just as long as the 
internal soldered flange. The object is to turn the bottom sides of the 
outer case into tabs that can be bent out. Driving a knife or chisel 
into the solderd seam will hopefully pry the flaps outward. Getting the 
corners loose would probably be the hard part. Cutting them as in my 
other method might be the easiest. With this method, after opening, I 
think you could then cut or melt of excess solder.off the main case and 
base, straighten the main case sides and get a good strong seam on 
reassembly.]

The blown oscillator I cut open had smt components inside. I replaced 
all the active devices and electrolytic caps I found in the circuit and 
checked to find that it worked again. (Yay!) I then was able to solder 
the top case back on the base. Not quite as strong as the original with 
just a narrow solder bead holding it, but working good as new.

Of course, if the oscillator's metal case is providing a hermetic seal, 
you loose that, but most aren't, anyway.

So I just thought I'd mention this other mechanical attack method. I 
think unsoldering the whole solder seal in one go and pulling it apart 
without damaging the internals is a pretty difficult task.

-Rex


On 2/19/2016 9:09 AM, timenut at metachaos.net wrote:
> Alex,
>
> I did not take opening pictures, but there is nothing to miss.
>
> For the outside of the unopened case, there are plenty of pictures on eBay.
> For the actual opening process, that consisted largely of scraping away solder
> with a small, triangular file and utility knife until most of what I could
> remove was gone and then using a hammer and screwdriver to separate the sides
> from the bottom and then prying it off. Nothing pretty, and nothing much for
> pictures. I used a tiny drill for my desoldering gun to remove an intial hole
> in the solder for the adjustment hole. I then enlarged it with a 1/16th drill
> bit (by hand). Ideally, a 2mm drill bit could be used. A 5/64th drill bit will
> fit through the hole, but it is very tight. Probably not best to drill with
> it because that would most likely enlarge the hole.
>
> I wouldn't open it the same way again, but I'm not sure of the best procedure
> that leaves the case and contents undamaged so that it can be reassembled. I
> think, perhaps, that I would remove all of the solder that I could as before.
> But then, I would make some sort of cut-out for the pins on the bottom and put
> it in a pan on the stove and heat it up (hopefully, evenly) until the bottom
> could be popped off. The outside case can get pretty hot without damage
> because the only contact is the pins and the inside gets pretty hot when
> running. The main risk is getting so hot that the plastic spacers on the pins
> melt or the pin supports melt. I'm not sure how hot that would be. But, they
> must have heated it fairly hot to melt the solder originally, so hopefully
> that would work.
>
> However, here are some pictures of the inside :) which is probably what you
> want!
>
> Top Case 1:    [img]http://imgur.com/mvQkJ16[/img]
> Top Case 2:    [img]http://imgur.com/K7Rmeau[/img]
> Bottom Case 1: [img]http://imgur.com/j7tC7QN[/img]
> Bottom Case 2: [img]http://imgur.com/TKiofvi[/img]
> Outer Oven 1:  [img]http://imgur.com/bzYywj7[/img]
> Outer Oven 2:  [img]http://imgur.com/kKKynzc[/img]
> Outer Oven 3:  [img]http://imgur.com/xtzFsXD[/img]
> Circuit Board: [img]http://imgur.com/PHgnVIm[/img]
>
>
> Mike
>
>