TMG Head Failure Analysis

butterman

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I recently had a head fail which was purchases used/refurb from Jag in march of 2019, I think this is a gen 1 head but maybe someone can confirm? I would also like to mention that Jags response was phenomenal and he had a new one in the mail within 12 hours, despite the crisis that is going on down in his home state of Texas.

Disclaimer: This is my opinion based on disassembly a single head with my limited knowledge of testing procedures of the product and guesses about the manufacturing processes of these heads. I could be COMPLETELY wrong about everything in this post. I welcome any feedback and I hope this discussion leads to a better product by TMG.

TL;DR: water ingress into head caused corrosion of internal components.

Symptoms of failure: the usual, blinking blue lights before blowing the fuse.

Tear Down:

IMG_20210301_110032.jpg


I removed the replaceable lens which revealed another plastic plug/ permanent lens underneath which was neatly sealed with and RTV
After cutting the RTV seal and prying off this cover I found moisture (what I assume is condensation) on the inside of the lens
IMG_20210301_111441.jpg
IMG_20210301_112030.jpg
IMG_20210301_112026.jpg


I was able to grab the pcb and pull it out which also pulled out a plug of RTV which sealed the cable to the back side of the head

IMG_20210301_111425.jpg
IMG_20210302_101145.jpg


There appears to be only two penetrations into the metal housing. The RTV'd front lense and the entrance for the cord which is potted with RTV.

IMG_20210302_101153.jpg
IMG_20210302_101236.jpg
IMG_20210302_101313.jpg


RTV'd plug - I assume the metal wire is crimped on to act as a stop when pulling the cord and pcb into the housing, it also reinforced the RTV. I believe I ripped the seal when I yanked it from the housing.
IMG_20210302_101407.jpg



Conclusions
This is my opinion based on a sample size of one. I cannot say conclusively whether this is a design flaw or a quality defect so I will only postulate a couple of failure modes.

1) These heads are "perfectly" sealed which can eventually cause moisture to become trapped and condense inside the head. I worked on a couple projects where this happened, we actually needed to add vents to the sealed enclosures to prevent moisture ingress. This is the same reason why you sometimes see tail lights on cars that are full of water.

Here is a description of the mechanism from Gore-tex
"When the internal pressure increases, the housing tries to equalize the pressure by drawing air inside. This causes stress on the seals and can lead to leak paths. Through these leak paths, a vacuum not only pulls in air, but also pulls in water vapor, which condenses inside the device. Once in liquid form, the water has no direct path to escape, so it collects inside the sealed housing and can eventually cause the electronics to short out."

What happens when electronics are not vented properly? (Video)

2) I noticed some movement of the RTV on the cable during disassembly, it seems the adhesion of rtv to the housing was defective and was not sealing. This could be where the moist air was entering or a direct path for water to enter through. due to my installation the back half of the detector is pretty well insulated from direct water contact and the break in RTV seal was, in my opinion, too small for water to penetrate.

Disclaimer 2
This is a sample size of ONE, in order to draw a more concrete conclusion it would be prudent to identify the failure mode from more samples. This could be a one off failure due to maybe a slip up in manufacturing or an out of tolerance part. There needs to be more samples collected to show how probable this failure mode is.

If anyone else would like to send me their failed heads I can disassemble them and post the results.

 

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89q2hiu54warefs

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Thanks for this, I live in a climate where heavy snow / salt in the winter is the norm, I'm hoping this is an edge case.
 

Vortex

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Wow, great job with the analysis! I wonder if this is also why my TMG Gen1 system is fried. I've got covers over all my LJ heads which should further protect against rain, but if the heads are drawing in water vapor regardless and don't have a good way to vent it, yeah that could be an issue.
 

bslaws

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@butterman where are you located? While I am not currently running any LJ system, I do run high quality LED driving and fog lights and have noticed during the winter they too get condensate build up visible on the front lenses. I assume this is happening because they are warm and as they cool, they draw in moisture. I expect them also to fail shortly.
 

butterman

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I'm in Boston, I meant to mention that in the original post
Post automatically merged:

Wow, great job with the analysis! I wonder if this is also why my TMG Gen1 system is fried. I've got covers over all my LJ heads which should further protect against rain, but if the heads are drawing in water vapor regardless and don't have a good way to vent it, yeah that could be an issue.

I'm happy to do a tear down on them, if you still have them
 

astronuts

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I’ve had 6 heads fail on me. I was an early adopter so I attributed the failures to that. Jag has always been top notch about customer service and replacements, but still. Water ingress would be a perfect explanation here. A recent head failure also took out the CPU. At this point all of the heads should be Gen2.
 

Mythic01

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Yikessss, this is painful to witness for anyone who lives in a harsher climate. Hopefully weather resistance improves.
 

Run4donut

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Living in a humid climate with G1 heads I'm taking note. I pulled one head from service due to some issues. I replaced the cable and hopefully the head works properly. If not I will crack it open and look for moisture.
 

Bloovy One

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To add a data point here.

I was also an early adopter of a 4 head system (order #50 on the first day as I recall) and now have (as my signature indicates) roughly 115K miles on the original heads installed in October 2018.

The car lives outside 24/7 and I drive between 3,500 feet elevation and 800 feet fairly often. I've been to sea level a few times and up to 7,000 feet a few as well.

No issues so far. I individually test them periodically. I lightly go over them with my powerwasher when washing the car. I have a rock scuff on the outer shell of one now. 🤷‍♂️
 
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chammerbeck

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I just took a look at mine.....used a laser tester to trigger the TMG system. Both units set off alerts. Tested each by covering them with something and alternated between them. I used my cell phone camera to try and see the jammers working. The only "bubble" "flashing" is the center one. I gather the large bubble is the receive. What's the side small bubble for?
I am gen1.......
 

TurboDriver

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I just took a look at mine.....used a laser tester to trigger the TMG system. Both units set off alerts. Tested each by covering them with something and alternated between them. I used my cell phone camera to try and see the jammers working. The only "bubble" "flashing" is the center one. I gather the large bubble is the receive. What's the side small bubble for?
I am gen1.......
Little side bubble is nothing but a bubble, just a placebo I suppose, no real purpose . In the beginning I think TMG toyed with the idea of a second transmit diode but opted for only one in production.

You are correct, center is transmit and oval bubble is receive.
 

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