# Bose Amp Circuit Board Conformal Coating Protection



## SwissJetPilot (Apr 27, 2014)

The Bose Amp issue of PCB failures has a long history with years of complaints posted in the Forum going all the way back to just a year or two after the Mk2 was introduced in 2006. Unfortunately, the Coupe stands out as being more prone this problem since it's more likely to get water in the boot for a couple of reasons; (1) the hatch and (2) Coupes are more likely to be out on winter roads than Roadsters, so the risk of salt water ingress for Coupes is higher. Throw in the additional problems of wet locations; (e.g. the UK or American Pacific Northwest) and various seals and grommets getting older and less pliable, the Amp doesn't really stand a chance.

I have included the following pictures of my Roadster to show the location of the Amp. For Coupe owners, it's in exactly the same location -

























While it might be easy to blame Bose for a badly designed product, Audi has to take partial blame for the location of the Amp. For whatever reason, Audi chose to place the Amp on the back side of the left rear wheel well, in close proximity to a large vent located directly aft of the Amp. Additionally, there are two grommets for the tail light right above the Amp, plus two drains for the spoiler, the antenna may also be suspect and of course the biggest opening and most common source of water ingress; the Coupe's rear hatch.

The rear vent (there's actually two - one on each side of the vehicle between the inner body panel and rear bumper) is located directly aft of the Amp. In normal operation, a low pressure area is created behind the car while driving. The pressure differential opens this one-way vent and draws air through and out of the vehicle. However if the little individual flaps become stuck open, water can make its way into the vehicle.

















Directly above the Amp are the tail light assembly bolt and the tail light wiring harness grommet. While they generally do a good job of keeping water out, it's been shown that if high pressure sprayer is used to wash the car, it can overcome the seals and water can get in. Then there's the antenna to consider. Rubber grommets are known to harden and become less pliable with age, thus reducing their ability properly seal and keep water out.

Another source, which seems to be a build quality issue, is the body chassis seam near the wheel well. Some people have done extensive water ingress tests to determine how and where water is getting in and in some cases this area has been identified as a source of water ingress.

So that leads us to finding some means to protect the Amp from water that we know will eventually get inside. Unlike most electrical component cases scattered throughout the TT, the Bose Amp housing is designed with vent holes to let heat out. Unfortunately, they also do a great job of letting moisture in. Here are a few home made plastic shields designed to protect the Amp, but I'm not convinced they're really 100% effective.

























These images of a disassembled Amp show the corrosion on the circuit board and aluminum housing due to exposure to salt and other contaminants that make their way onto the unit. The corrosion is detrimental the performance of the Amp and can become so severe as to destroy the PCB, circuit traces and IC components. For anyone who's noticed a change in their sound system performance, e.g. crackling noises, failed speakers, loss of volume control, or other unexplained sound system failures, it's worth removing and opening the Amp and checking the state of the PCB.

Even if the Amp housing looks okay, it's worth visually inspecting the PC board and components for corrosion damage, especially round the large ICs, IC connectors (legs) and circuit board traces. It should be noted in the pictures below the white material on the large ICs is thermal paste and is supposed to be there. It allows the IC to transfer and dissipate heat to the aluminum housing. You can see the four white rectangles on the inside of the housing where it contacts the ICs.

For anyone with the skills and willingness to try, there have been successful repairs of badly corroded PC board and components. You can read more about it here -
https://www.ttforum.co.uk/forum/viewtop ... 3&t=556713

If you're not sure you can master these skills, this company has been recommended a number of Forum members who seemed quite happy with the service they provided -
https://boserepairexperts.eu/

































Which brings me to the possible solution of DIY conformal coating. The first image is a black conformal coating applied to a commercially repaired Bose Amp circuit board. The image below that one is a clear silicone conformal coating applied to a Drone PC board.

A conformal coating is basically an epoxy or silicone based coating applied to the entire PCB which covers the circuit board and all the components. This effectively seals and protects everything from the environment. While common for military and harsh environment applications, this is generally done at the PCB fabrication facility. While there are a number of materials which can be used for conformal coating, not all are suitable for a DIY application.

















One option that looks promising is currently being used for Drone PCBs. This is a DIY method of applying a silicon based conformal coating from MG Chemicals called Silicone Modified Conformal Coating (#442B). This is a one-part, acrylic-silicone blend conformal coating which is easy to apply and cures in about 30 minutes. It can be removed with appropriate strippers, or soldered through for repair or rework. 422B provides strong protection against moisture, corrosion, fungus, dirt, dust, thermal shock, and has been tested in salt spray environment with no oxidation or coating damage. Another cool feature of the material is it will fluoresce under UV light, so you can check to see if you've applied the coating properly.









Here are some links for cleaning the PCB to ensure if there is any corrosion, it's completely removed before applying the conformal coating. And a some links on how to apply it along with a contact point of purchase. I have seen it on Amazon so it should be relatively easy to purchase online.

Conformal Coating Tutorial -
https://oscarliang.com/waterproofing-drone-electronics/
PCB Corrosion Causes and Cleaning -
https://www.mclpcb.com/pcb-corrosion/
422B - SILICONE MODIFIED CONFORMAL COATING
https://www.mgchemicals.com/products/co ... ating-422b
How to Waterproof Electronics -




Inspecting Conformal Coating with UV Light -





If anyone does give this a go, please be sure to post your DIY steps and process so we can see how you did it and how well it's worked out.

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## TTsdsgomg (Mar 19, 2013)

SJP or can I call you Swiss, as usual that is a comprehensive, detailed and thorough write up and I salute you sir [smiley=dude.gif]


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## SwissJetPilot (Apr 27, 2014)

Quite welcome.


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## Wolvez (Jun 22, 2018)

Best way to protect it is by isolating the amp to the body ground without losing thermal conductivity to the body. It's air-cooled thick coating will overheat the amp. It's protected using Polyphenyl Ether (PPE).


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## SwissJetPilot (Apr 27, 2014)

I've managed to get in touch with Bose Customer Service and have sent them the information about the DIY conformal coating to see what they say. Here's their reply -

*-----------------------From Bose Customer Service -*

_Concerning your question to apply a conformal coating to the PCB, we cannot give you an answer since we do not have any experience in that direction and additionally we would like to refrain from making any suggestions to modify components._

I also contacted Bose Repair Experts in the UK to get their opinion the MG #442 material and also what thermal paste to apply to the four large ICs (Output Modules) when putting the unit back together. Here's their reply -

*----------------------- From Bose Repair Experts -*

_MG Chemicals product Silicone Modified Conformal Coating (#442) is very similar to what we use. Just make sure the tops of the four output modules; (e.g. U24, U25, U26 & U27) stay clean of any coating.

To ensure good contact between the four output modules and the aluminum cover use Arctic Silver Paste MX4 ... just a thin layer though .

284 Leith Walk
Edinburgh, Scotland EH6 5BX
0131 553 2126 / 0330 808 4151
http://www.boserepairexperts.eu
_


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## Tri-Chas (May 26, 2010)

Excellent article.... thought this might be handy for someone to know:

If you need to (as I did) get your Bose amp repaired try... https://boserepairexperts.eu/audi-tt-bo ... er-repair/

This was a couple of years ago, all fixed and a great service, when I re-installed, I took the advice of another forum member and cut open a large 2 litre plastic bottle and fixed around amp with cable ties. Works well as its stiff enough not to move, keeps the water off, and allows good airflow.


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## SwissJetPilot (Apr 27, 2014)

Got another piece of good advice about protecting the outside of the Amp from water. There was mention of a plastic shield of some sort which Audi offered to help keep out of the Amp. So I asked Bose Repair Experts if they knew anything about it -

*------------------Their reply - *

_All they offered was a plastic sheet that draped over the top ... we use something called "Flashband " which you can get easily ... 100 mm width is fine._

Below is a picture of Flashband from the ScrewFix website. Evidently it's used for roofing repair and has an adhesive backing and can be cut to shape easily with just a pair of scissors. I have no experience with this material so if anyone wants to give this a try to make their own Amp water shield, please be sure to post your results.

https://www.screwfix.com/p/bostik-flash ... 00mm/57969









From this video, it seems easy enough to work with. Easy to shape and form so it might just do the trick.






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## arpuc (Jun 14, 2014)

SwissJetPilot said:


> Got another piece of good advice about protecting the outside of the Amp from water. There was mention of a plastic shield of some sort which Audi offered to help keep out of the Amp. So I asked Bose Repair Experts if they knew anything about it -
> 
> *------------------Their reply - *
> 
> ...


Very interesting, did they give any clue how it was applied? Sticking it direct to the amp might cause issues with heat build up I would have thought.


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## SwissJetPilot (Apr 27, 2014)

No, unfortunately not. But from the YouTube video, I suspect it can be formed over the Amp easily enough. If you go with the wider version of Flashband (250-mm) it may be possible to form it over the sides to it just stays in place without the adhesive.


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## TTsdsgomg (Mar 19, 2013)

SwissJetPilot said:


> No, unfortunately not. But from the YouTube video, I suspect it can be formed over the Amp easily enough. If you go with the wider version of Flashband (250-mm) it may be possible to form it over the sides to it just stays in place without the adhesive.


Just a word of warning. I have used this stuff .... on a roof and it can get messy, mainly because of the very high tack value ie. its very sticky and likely to leave residue on stuff. Personally I would not use it, only maybe to seal the body work from leaks, but definitely not stuck to the amp. Just my two pennyworth :?


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## TTsdsgomg (Mar 19, 2013)

I have had no issues with my roadster bose system in 5 years plus and that may be as Swiss suggests owing to different rear bodywork to coupe. I have still constructed a loose fitting plastic shield to protect from 'drips' just in case.
There are a number of posts regarding protecting the amp and prevention is definitely better than cure £££ 

https://www.ttforum.co.uk/forum/viewtop ... &t=1847165


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## SwissJetPilot (Apr 27, 2014)

To your point of the tacky issue with the Flashband, would it be possible to stick kitchen aluminum foil on the adhesive side? This way it wouldn't be glued to the Amp and could be formed over the Amp in such a way that it stays in place.

Based on the airflow, I would think as long as the trunk side panel air slots and the rear vent are not blocked, there should be sufficient cooling around the Amp. Evidently Audi didn't see fit to insist on a fan for it as they have with some Bose Amps. Although I question just how much air is passing over the Amp on the Roadster since the trunk are is basically a sealed off area. At least the Coupes get decent airflow through the entire cabin.


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## TTsdsgomg (Mar 19, 2013)

Swiss, yes you could stick foil or some other material on the sticky side, and on the plus side this stuff is meant to mimic lead flashing so it does hold a shape and can be formed, its just the ferocity of the adhesive, it sticks to brickwork etc. 
For me it's overkill and if stuck to the amp might lead to other probs, but each will decide on their preferred solution.
I'm following your original advice and ordered this .... and will mask top of chips and use 'Artic Silver' heat paste.


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## SwissJetPilot (Apr 27, 2014)

From the YouTube video, it looks like that adhesive is really aggressive which makes sense given what it's intended to do.

I will be interested in your results with the spray. Can you inspect it with UV light to ensure good coverage? Any pictures of your project would be a great addition!


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## TTsdsgomg (Mar 19, 2013)

SwissJetPilot said:


> From the YouTube video, it looks like that adhesive is really aggressive which makes sense given what it's intended to do.
> 
> I will be interested in your results with the spray. Can you inspect it with UV light to ensure good coverage? Any pictures of your project would be a great addition!


Ok had 1 hour to fiddle and added conformal coating, also gave chance to check board.
I used paint-on corformal and a fine brush and applied to chip legs and small area as spray seemed bit overkill.
Also used existing factory heat paste as was still moist, just re-spread it.
There appears to be some sort of factory coating ( see red arrows pics 7-8 )
Refitted my belt & braces plastic drip shield. :roll: 
There was no signs of any damage around the chips, but there was some signs of a very small amount of a white powdery substance on heat sink :roll: ... it looks atmospheric and not water drip related. Maybe slight condensation, anyway added a desiccant pack too.


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## SwissJetPilot (Apr 27, 2014)

Very nice! Looks like you did a really good job. [smiley=thumbsup.gif]


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## ryguy (Sep 21, 2020)

To those who have performed this mod, how has your amplifier performed over the past 1+ years? I am getting ready to do this myself and have a quick question. If I mask the ICs/output modules/processors, do I spray/coat the entire board (save for the actual connector) both front and back? I have plenty of Arctic Silver Céramique to ensure the modules transfer heat properly to the heatsink. Is there anywhere on the board (except across the top of the 4x modules) that I SHOULD NOT spray?


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## ryguy (Sep 21, 2020)

Anyone? Anyone? Bueller? What are your thoughts, @SwissJetPilot ?


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## SwissJetPilot (Apr 27, 2014)

@ *ryguy* - I haven't actually done this since failed Bose Amps isn't really a problem for Roadster owners.


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## Bfince (Dec 18, 2019)

Thank you swissjetpilot for your detailed guide. Coincidentally I thought the same method after two times of bose amp repair (and yes I'm using the conformal silicone coating for years for drones and outdoor circuitary like wifi ap's). Repair garage suggested to cover the top of the amp like an umbrella but it seems like the dew / moisture is the main problem due to vents. Especially in cold weather. And yes roadster owners rarely have this problem because coupe trunk is directly connected to cabin. Cold aluminum body of the car and cold vent air, cold aluminum Bose case, warm moist cabin atmosphere... do the math.

FYI acrylic conformal coating is not a good option for a "high thermal variable" pcb, like amps or cpu/gpu boards. Silicone is much more flexible. (you can use the suggested product in the first entry, or people -like me- who can not get that because of the regional limitations may use Becoat 921L as a cheaper alternative - https://encapsulant.com/solution/automo ... ic-module/)

As mentioned before (Bose's answer) cover the heatsink connecting surfaces with masking tape before application. Remove the tapes and repaste with thermal component after curing completes.

As conclusion: conformal coating may be the only long term solution for that
(Alternative: totally remodel the aluminum bose case from plastic and use seperated heatsinks for the IC's )


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## Bfince (Dec 18, 2019)

ryguy said:


> To those who have performed this mod, how has your amplifier performed over the past 1+ years? I am getting ready to do this myself and have a quick question. If I mask the ICs/output modules/processors, do I spray/coat the entire board (save for the actual connector) both front and back? I have plenty of Arctic Silver Céramique to ensure the modules transfer heat properly to the heatsink. Is there anywhere on the board (except across the top of the 4x modules) that I SHOULD NOT spray?


Quick answer: no, 
you can spray front and back of the pcb if you cover modules with masking tape.


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## ryguy (Sep 21, 2020)

Bfince said:


> ryguy said:
> 
> 
> > To those who have performed this mod, how has your amplifier performed over the past 1+ years? I am getting ready to do this myself and have a quick question. If I mask the ICs/output modules/processors, do I spray/coat the entire board (save for the actual connector) both front and back? I have plenty of Arctic Silver Céramique to ensure the modules transfer heat properly to the heatsink. Is there anywhere on the board (except across the top of the 4x modules) that I SHOULD NOT spray?
> ...


Awesome! Thanks for the info. Will be performing this mod very soon.


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