fixing fried electronics

circuit boards have never been a specialty of mine. as a matter of fact, other than re-flowing cold solder joints on neon instrument clusters, ive never messed with them. or had much luck with solder. 

however, since a wise man once told me that you cant make something broken work LESS than it does now, im willing to try. 

what we have here is a failed module on a seat motor in my 1999 528i. everything else in the system is good, however the motor wont operate via the seat controls due to this module of unidentified purpose. 

in all honesty, i dont care what its purpose is supposed to be, as the only purpose its currently serving is to make my short, fat ass not be able to reach the pedals comfortably because the seat wont move (i have a workaround, but i want to FIX it, not hack it)

since im cheap, id like to try to fix the burned up piece instead of replacing the whole module. unless someone has a free one. or can find me a cheap, known good. regardless, id still ike to try to fix it. 

attached are the pictures of motor, part numbers on module, and burned up piece. can yall help me identify what the component on the board is that fried, ad where to get a replacememnt? maybe even a how to on how to work with circuit boards?

20180731_151055 by Michael Crawford, on Flickr

20180731_153303 by Michael Crawford, on Flickr

20180731_153310 by Michael Crawford, on Flickr

It's  a little difficult to tell since it's burned up  but it appears to be a resistor.  You need to find a schematic that identifies the resistance and current capacity of the resistor in order to replace it.  Having said that resistors don't often just go bad on their own, chances are the failure of something else on the board caused too much current to pass through the resistor.

Hmm.....

Since i cant even find a part name, a diagram may be just shy of impossible.  

If you can make out the colors of the lines on the resistor you can tell it's resistance.

Doesn't help with rated wattage, but see if you can see the colors. 

Does the motor turn if you apply 12v?

The motor and tracks all work perfectly with directly applied 12 volts. Both forward and backward for the full range of motion. I'm unable to see any colors through the burning

Does the passenger seat have a matching module to reference?

Ooooooo.....

Dunno. Havent looked. But GREAT idea!

Just in case you haven't checked, electronic components sometimes explode for a reason.  Did something draw way too much power through that particular thing at some point?  If you follow the traces on the circuit board, you should eventually come to a couple of pins on the connector.  Figure out what those go to, and make sure its not drawing too much power.  If both circuits just head into a chip, it is probably just an internal failure, but its worth taking the time to check.  Pain in the ass to figure it out, replace the component, and then let the smoke out of it again.

I have a guy in town that I race with who does electronic controls for industrial applications.  When I have a blowed up thing on a circuit board, i visit him, he figures out what it is, and gets out the Mouser catalogue.  Maybe someone in your neighborhood does such things?

stuart in mn said:

It's  a little difficult to tell since it's burned up  but it appears to be a resistor.  You need to find a schematic that identifies the resistance and current capacity of the resistor in order to replace it.  Having said that resistors don't often just go bad on their own, chances are the failure of something else on the board caused too much current to pass through the resistor.

I’ll add that it appears to be surface-mount too, which is more tricky to replace. 

Part number is likely the PA66-GF25,  appears to be a voltage regulator or motor controller board of some type.  Unfortunately I can't find much on an english language website to figure out much more than that.    Just by the little I can find, I am guessing it steps the 12v car voltage up to 24v for the motor, which is a common motor voltage in Europe.  Plus handles the polarity for moving the seat forward or backward.

The resistor is toast of course, but something made that happen.  Could be a failed motor, or the Elmost 10017C voltage regulator.   

In reply to Streetwiseguy :

Theres a tv repair giy that has fixed soud boards and other equipment for the church.  Ill see if hes still around 

Regarding the surface mount parts: I worked as an electronics assembly tech for 6 months or so one summer not too long ago, and we primarily did SMT stuff. Way easier to work with in volume, since the pick and place machine can do just that (and doesn't have do deal with bending the leads). I ended up doing a lot of reworking of defective boards with lots of parts (like, 200 unique components populating both sides of a quad layer PCB the side of business card).

To work with SMT parts the easy way, you'll need a set of tweezers (there are ESD safe sets out there), and a little hot air gun device like this: https://www.amazon.com/Soldering-Station-Digital-Solder-Welding/dp/B07F3WLX7H/ref=sr_1_9?ie=UTF8&qid=1533096546&sr=8-9&keywords=smt+hot+air+gun

That's just the first chinesium one I pulled up on Amazon, but looks very similar to the ones I've used at a couple jobs. Put the patient on a level surface (I like natural wood, as it won't store heat to bite you with later or release nasty plastic fumes). Use the tweezers to pull up the old part after the solder reflows. Using a soldering iron with appropriately fine tip, you can now removed any excess / old solder carefully if desired (be gentle, don't rip up any pads). Add new solder paste, or if using the old solder a tiny bit of flux, and place the new part. Heat with gun until it reflows. Voila, you've hopefully fixed the thing! Clean off any flux / solder balls for longevity and you're done.

I find this way easier than dealing with solder wick / sucker guns and wishing for a third hand as I often do when working with through hole components. There are other methods than what I described, including using tweezers with heated tips, but that's a quick description of what has worked for me.

In reply to hhaase :

PA66-GF25 is the designator for the type of plastic.  It's Nylon 6,6, glass fiber content of 25%.

The part number is on the sticker under his thumb in the last photo.  Bosch PNs, at least of that era, are all 0 xxx yyy zzz.

hhaase said:

Part number is likely the PA66-GF25,  

Nope, refers to the plastic used. In this case, is polyamide 6/6, or nylon 6/6-which is how the polymer chain is oriented with its appendage off the benzene ring, and it’s glass filled 25% by volume (if I remember my plastics education correctly)...

Im going to try to get to the tv repair shop today and see if hes willing.  If that fails, ill try my workaround while waiting for the junkyard to get an e39 with seats in it. That will at least let my drive the car and focus on other issues.

In reply to Dusterbd13 :

there's always someone parting an E39 on CL.  that module is probably also used on E38.  Take the module part number and punch it into the BMW parts catalog on realoem.com to get a "where used" list.   and like Forrest Gump, that's all i got to say about that.