Hello all,

a little while ago and thanks to this forum, I succeeded in repairing my passenger seat module, thus restoring all movement and heating to the passenger seat.

Whoopee. However, the memory function is still not working as it should, which prompted me to address the driver's seat module... and this time I think I'm in over my head. What I found was this:



Remarkably enough, the module works fine as far as seat movement is concerned, but clearly some overheating has been going on.

So what I'm wondering now is

- what sort of component is the disc-looking thing that looks burnt-out, what does it do and why might it have overheated (by way of preventing it from happening again)

- is said component replaceable/fixable, say, if one were to reinsulate it with, let's say, epoxy or conformal coating, seeing as apparently the "shell" of the component has been burned off but the innards work... I know, crazy idea, but I still thought I'd ask...

- would it be safe to use the module as-is, or would I be sitting on a fire waiting to happen?

- I have a feeling I'm going to end up looking for a new seat module. If so, is there anything I need to be aware of, other than needing an LJE2160AB/XXX or later (AC/AD...)

I'm sure I'll come up with additional questions immediately after hitting "Submit". For now, I greatly appreciate your opinion(s).

/Per

 

Looks like capacitor. You can check by looking into the other module. You will need the capacity marking to find a replacement. Looks like 2 soldering spots, so a repair looks like the way to go...

 

You are fortunate not to have caused a fire with that damage. I plugged in my seat module after using a jump wire inside due to worn traces and I could visibly see the interior of the module glow when I tested it (from the outside of the case), yet after taking the case back apart on mine there was no visible damage.

I happen to have the blown module open from my project. Here are a few pictures of the capacitor. Looks like the numbers on mine are:

S14
K14
Auto
0507

These pictures are from a seat module off of a 2006 XK8. The seat module code is LJE2160AB/xxx, so should be the same as yours.

 

Varistor (voltage-dependent resistor):
https://www.ebay.com/itm/S14K14-AUTO...-/401063922018

As chilly says, lucky the damage is very localised, and an easy, cheap fix for the fried component.
May not resolve the memory issue though.

Varistor is a form of voltage surge protection.

 

Excellent! Varistor is ordered and on it's way as well as a new module lid to replace the old, cracked one.

I understand now that the varistor was just doing it it's job - thankfully I suppose, or the whole module might have been toasted/on fire. Any idea what might have caused this kind of voltage surge?

Chillyphilly - I find it a bit disconcerting that your module was overheating *after* you wire jumpered a broken trace, since the repair I did on my PSM looks exactly like the one in your pic. Did you ever find out what was causing your module to glow? Presumably (hopefully), something unrelated to the fix?

In any case, I'll be checking these modules regularly by hand to see if they get hot.

Again, thanks all for your help!

 

I'm all about repairing small components and saving some dough, but that certainly would have me a bit concerned as to what caused yours to blow in the first place. If you are set to repair, best thing to do is monitor it closely as you said, especially during and directly after using seat controls. I am surprised all the seat functions worked, minus the memory. Did the memory buttons on the door work at all during your car ownership?

As for mine going kaput, I just chalked it up on a faulty solder on my part, perhaps I bridged another line on accident, though it didn't look that way. It blew right after I plugged it in after the repair. My reclining adjustment did not work so I was trying to remedy it, everything else worked.

 

Phillip (IIRC), yes, the memory function has indeed worked for seat positioning while I've had the car (going on 4 years in March). I have never used it much, so I don't really know when it stopped working.

In fact, memory still does work for steering wheel positioning, although limited by the quirkiness of that particular system, i.e. jerky, erratic, stop-and-go behavior - so it does remember positions "1" and "2", just has trouble getting there. Another fix on the list.

I'm bent on trying to fix the seat module for starters. Will try to take great care soldering and plug it back in without the lid the first time so I can have a better idea what's going on.

I'm thinking (guessing) the module damage might have to do with water ingress or perhaps might somehow be related to the folding mirror issue I had.

I mean, surely it couldn't have to do with plugging in an OBDII reader with the ignition on... nah... not even... if done repeatedly, in ignorance...

Thanks again for helping.

/Per

 

It may have been like that for some time: the module will still work without it, although obviously without the circuit protection it affords. Varistors are frequently used to catch voltage spikes that can occur around motors being switched - in this case the seat motors.

Try to clean off the vapourised metal on the board with a little meths or isopropyl alcohol before you fit the new one.

If you're interested in the theory behind them, this tutorial wil give you an insight:
http://www.electronics-tutorials.ws/.../varistor.html

Chilly, your short may be here:

although I can't see anything that looks like it glowed? Is the back of the board intact?

 

Thanks for the tip, Michael, though I am not all too sure what I am looking for..? That looks to be a clean solder joint on to the trace with no bridging to others? Perhaps my eye sight is going sooner than I had hoped.

In all fairness I had a second jumper wire installed in a second place which I had pulled off after the board fry. It may have shorted from the other one (seen in the lower left of the board, same side).

When I had plugged it in it had a couple of very distinct glow spots I could see through the case, I think coming from the same place, but who knows. Along with it came what sounded like a relay switching on and off several times...I thought the sound originated from the board, but it could very well have come from under the seat.

Sorry to hijack the thread.

Here is a picture of the back of the board, and a picture pointing where the other jump wire ends had been:

 

Michaelh, thanks for the edification. My optimistic conclusion is that, since the unprotected module is not complete toast, the voltage surge probably has not reoccurred.

I will be at the ready with the cotton swabs and the IPA to clean up the board before (and after) soldering.

Chilly, I tend to agree with michaelh on this one. Wouldn't hurt to try and resolder that joint being a bit more parsimonious with the solder.
As regards eyesight, I found a digital USB microscope to be invaluable in both examining the PCB tracks for corrosion/continuity as well as for the actual soldering.

 

New component in place, board all cleaned up, everything is working and so far nothing gets hot
I had to bend the varistor more than I really wanted to for it to fit inside the casing. It sort of looks like it's about to faint, or had a bit too much to drink. The soldering joints seem to have held up fine, though.
Fingers crossed. Thanks again everyone!

 

That's cleaned up remarkably. It was looking terminal in your post #1.

Good to hear it's working and staying cool.

Graham

 

Good job.
It will be fine in that position.