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Posted: 5/21/2020 3:31:56 PM EDT
So I figured I would do some tinkering with the USGI compass assembly for the PVS-14/7 in the interest of making it suck less. I figured I'd share my lessons here and give some options to guys that want to use the compass module. Here is the module I am discussing in this post:

The first thing you are going to have to do is break the epoxy seal on your compass unit and open it up. If it's never been opened up before, it's a bit of a pain to get it popped open. I saw a video on Youtube where a guy just gently pries the bottom cap off with a utility knife blade. Yeah, that WON'T work! The way he showed it easily popping off is only AFTER you've already broken the epoxy seal. It's gonna require a lot more force that you can or will want to safely apply with a thin utility blade. What I did was take a sharp flathead screwdriver, place it in between the body and the bottom cap, point the screwdriver down, and press down on the cap with the screwdriver pushing away from the bottom of the unit. I did this at 4 positions on the circular body - 12, 3, 6, and 9 o'clock. Slowly pushing in each equidistant area helped crack the epoxy band and get the bottom cap off. Here is what it looks like separated, notice the green epoxy ring you'll find in there:

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Link Posted: 5/21/2020 3:33:31 PM EDT
Remove the epoxy ring or all pieces of the epoxy and discard it. The actual LED light module should just lift out of the bottom cap at this point.

Now the first thing I would do when the unit is apart is check the battery and replace if need be. This compass module uses what is called a "pin battery" BR425. If you search for BR425 you should have no problem finding replacements as these are commonly used in fishing lures. My battery tested right at 3.22 volts, perfectly "fresh" and ready to use! Note the actual "pin" sticking out is the negative terminal, and the body/case is positive. You'll also have to remove the battery prior to testing to get an accurate reading. I also noted that the battery installed in the unit at the factory is marked "National lithium battery" That's probably the reason why these units are still glowing bright 10+ years later - good lithium batteries and their low self discharge rate. Here is the factory battery along with the LED unit it's installed in:

Now on to the second thing once you have your battery tested: the button on the bottom SUCKS! Like, kills your finger to use it for more than a half second kind of sucks. The button itself isn't really a button. Rather, it's a force-sensing resistor pad as you can see in the above picture. That "grid" looking thing is the force-sensing resistor. The "button" you see from the outside is just a raised piece of the plastic bottom cap. You just press in to indent the bottom cap and push it into this grid.

In order to make the button require less pressure to operate, put a few layers of electrical tape on the inside of the bottom cap you removed:

3 layers of my cheap Harbor Freight electrical tape worked perfectly - makes it a LOT easier to turn the light on.

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Link Posted: 5/21/2020 3:34:41 PM EDT
Now at this point, you should have a good working battery and a button that doesn't suck anymore. The bottom cap will just snap back on when you are done. Just remember that there is an indexing tab that will need to line up when putting the LED module and cap back in the compass housing. If you are worried about making it rugged and waterproof, you could seal it with some silicone caulk or something similar. I just use the cap the way it is without epoxy.

A member posted a long time ago that someone should try tritium in the compass module. And, I just so happen to have some tritium tubes laying around for gun sight projects. So, I figure I'd try it out and see how well it works! Here you'll see I affixed a tritium tube right over the LED using clear packing tape:

I believe the tube size is 0.5x5mm It seems to fit perfectly over the LED area and I put everything back together to test it out. And, it seems to work well! Here is that it looks like in my basement through my PVS-14 with low light:

It's lit up nice and bright regardless of how high or low the gain is set on my tube. Here is a better contrast shot over a pitch black area:

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Link Posted: 5/21/2020 3:35:41 PM EDT
So for those of you that want a "constant on" compass module, this seems to be a viable option! The only obvious flaw is that you can't turn it off - your compass bearing will always be floating there in your image. You could always place a small strip of black electrical tape at the top of the unit where the light exits in order to "turn off" the unit if you ever wanted to. But, the easiest thing to do would be to just remove the compass unit at that point. For those of you that don't know, the half-life of tritium is 12 years. So if you had new factory fresh tubes, you'd get 12 years of use before you see the light start to dim down.

Hopefully this post will help others out. Please feel free to ask any questions you may have.
Link Posted: 5/21/2020 3:50:26 PM EDT
I always debated removing the pressure resistor and putting a click button in its place amd drilling the batter cover.
Link Posted: 5/21/2020 3:52:32 PM EDT

Not sure why I'd need this, or when, but I like the option.  Where'd you get the compass?
Link Posted: 5/21/2020 4:05:51 PM EDT
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Originally Posted By pbjunkiee:
I always debated removing the pressure resistor and putting a click button in its place amd drilling the batter cover.
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I was thinking about this as well. But, you can pretty much forget about water resistance at that point. I can't find a switch small enough for the unit that's also waterproof. So, I went the Tritium route!
Link Posted: 5/21/2020 4:06:39 PM EDT
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Originally Posted By NotIssued:

Not sure why I'd need this, or when, but I like the option.  Where'd you get the compass?
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Ebay my friend! I believe I got mine for $35 shipped new in package. They can regularly be had for around that price.
Link Posted: 5/21/2020 4:25:57 PM EDT
[Last Edit: 5/21/2020 4:39:53 PM EDT by TNVC_Augee]
Link Posted: 5/21/2020 5:31:13 PM EDT
Cool thread 👍👍

I’ve actually come to like the compass on my translating lens Sentinel. I don’t use it often but when I have it’ll definitely get you in the general direction. I have a couple and I’m going to open one up and do the tape trick.
Link Posted: 5/22/2020 8:41:46 AM EDT
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Originally Posted By TNVC_Augee:
Always glad to see tinkering and fun projects, and I don't actually hate the compass unit, and will still use one depending on what I'm doing.

That being said, I would recommend against running it too much with the "tritium mod" to make the compass "constant on," as you'll end up burning the shadow of the compass display into your tube--it's just like leaving an image paused on an analog television for too long, as long as the image is in motion, it's a non-issue, but even if it's at a "safe" level of illumination, it will eventually leave its mark on the analog tube.

This is the same reason some claim that the COTI can cause long term tube damage--if you leave the compass display constant on, or if you consistently run it too bright so that you have the illuminated field of view constantly for a long duration (ideally, you would reduce the gain of the COTI to where the "FOV" is not visible or barely visible most of time--it also adjusts brightness/gain automatically).

Beyond that, I actually like the USGI compass requiring a little force to activate versus activating too easily--I'm not necessarily using mine for dead-reckoning navigation when I'm using it, it's more of a quick general azimuth check, so a quick squeeze and read is all I need. That being said, some can definitely be a little stiff, especially when they're reaching the end of their life.  

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Thanks! I completely forgot about the "burn-in" effect these tubes have. How often does one have to have an image in one single spot before things start to "burn in"? I assume the same thing can happen if you use your night vision device behind a "red dot" style aiming device for long periods of time? Either way, I guess I'll ditch the tritium mod all together then.

Link Posted: 5/22/2020 12:30:03 PM EDT
I got my PVS-7s about 14 years ago now and they came with that compass.  I had no idea it uses a pressure pad to activate!  So I went into a dark room just now to test it out.  I do have something kind of lighting up when I push on it, but its is completely fuzzy and at the edge of the field of view.  I tried moving my focus all the way each way and I couldn't get any kind of readout from the compass.  

Any ideas?
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