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Decrease your chances of CEM or DIM failure with a FAN

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mrbrian200
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Volvo Repair Database Decrease your chances of CEM or DIM failure with a FAN

Post by mrbrian200 » Thu Jun 15, 2017 1:55 pm

I've come across several reports by owners who state when their CEM or DIM freaks out/acts up they discover a pool of superheated air trapped up behind the dash where these modules are. When things cool off normal functionality often returns.

I'm not having problems with the CEM or DIM on mine (MYO6 S60), this would be considered a 'preemptive strike'.

I decided to lessen my chances of having problems down the road with a simple fan to keep this pool of super heated air from collecting back there in the first place. The CEM is considered a low power design probably less than 40w of total thermal load to dissipate. The DIM would be in the same neighborhood considering it's filled with incandescent bulbs. They don't need a dedicated fan pushing air directly into their housings like a high performance PC/laptop. They just need a modest flow of fresh air in their general area.
FAN.JPG
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Hence a 120mm silent higher CFM computer fan which makes a breeze you can feel tied into the 12V power port circuit (on at KP I/II only). Held securely by cable ties to keep it from wandering into the steering mechanism. 0.4A isn't going to break the bank with regard to electrical overhead on the car. Though directed specifically at the CEM, the DIM and center stack components should also benefit as the air behind entire front console is no longer standing/stagnant.

Now for the longer more technical reasons of why a fan should lessen the chances of future problems. Computer nerds/EEs can skip this you already know.

Thermal stress events damage chips and also solder points on the board. Each time a severe heat event occurs silicon transistor junctions in the microchip degrade a little bit after which more current passes through various transistor junctions even at normal operating temperatures, generating more heat and making it even more prone to future events and possible total failure. The effects are cumulative with each event. Heat spikes can also cause solder joints to fracture and lose electrical contact. Boards flex and expand with heat. Fractured solder loses contact.

I'm not talking about 110F inside a parked car. I'm talking about higher temperatures that might be seen in limited areas inside the actual modules/microchip internals.
Add ambient air temperature of superheated air trapped behind the dash (probably in the 120-130F range) and temperatures inside these modules are probably approaching the breaking point (over 100C/200F).

Also potentially in play: MCP/CPU senses it's getting too hot and underclocks or halts to prevent a catastrophic current/thermal runaway (the chip would otherwise burn itself up--literally). I think this is what's happening when people's CEM cuts out completely while driving and consistently comes back to life after sitting for short while.

EE from Xemodex could probably key in/confirm this is indeed what is happening on some units. They install an oversized heat sink to the MCU inside their rebuilt CEMs to keep the chip temperature in the safe zone.

However, the best policy as it would seem to me, would be to prevent these extreme thermal events from occurring in the first place after which extreme measures become necessary to keep it working. Hence an elegant simple little solution: a 12V computer chassis fan. If ambient air temp is kept in check, the modules internals will more likely stay in the safe zone too.



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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by matthew1 » Thu Jun 15, 2017 2:00 pm

Very cool (heh, get it?) Brian. I'll put this in the Repair Database.


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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by mrbrian200 » Thu Jun 22, 2017 1:19 pm

I'm noticing when changing audio CDs they aren't super hot when they spit out of the AUM like they used to be either. Now they're just warm.

It wouldn't take much to design a custom plastic bracket bundled with a silent fan and offer it in the aftermarket to make it easy for people. It could hold onto the rear of the lower trim panel in the space where I put this one with some sort of hook or catch that goes around the backside of the CEM to keep it from sliding over into the steering mechanism. With a little research I bet there's an open fuse positon right there on the CEM that ties into this circuit and can be tapped. I used an in-line glass fuse holder on this @ 1A.



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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by Georgeandkira » Tue Aug 08, 2017 4:33 am

Did you make the shroud? I've only seen "squared off" black fans in my travels.



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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by ndphotonl » Thu Jun 07, 2018 11:28 am

Does a S80 from 2001 suffer from these problems? If so, I will probably also execute this mod.


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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by mrbrian200 » Thu Jun 07, 2018 10:18 pm

2001 S80 is a different style module in the same general location. Failures aren't as common as the later version (I think), but it can happen. The worst offenders are the newer style centered around 2004. I couldn't hurt.



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Re: Decrease your chances of CEM or DIM failure with a FAN

Post by ndphotonl » Fri Jun 08, 2018 2:08 pm

Thanks! A little airflow wouldn't hurt a bit, I will check if 120mm fits easily, else I will try a 80mm fan I have lying around.


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