Success in General Module Repair

[mnewman]

I've gone and added pictures back to the original post (as well as my FTP harness HOWTO) that are locally hosted here, so hopefully they'll stay (they're attachments though, not fully inline)

Thank you all for this awesome post.

[mnewman]

I completed the CAP repair on the GM last Friday. IMHO it was not too difficult, clearing the old Solder from the board was the toughest part in my experience. Took me about 2 hours to get the CAPS replaced. I had a solder sucker but didn't work too well so ended up using the Copper solder remover to complete the job. Thanks to all who contributed to this post!

IMG_1598.jpg

[DavesNotHere]

Just about to get started on re-capping my GM2 (yes, it was cold out yesterday, the windows wouldn't move and the trunk relay was clicking... grrr). Ordering Vishay caps from Newark.
Questions: Are the repairers here using a Urethane conformal coating (which is what it looks like is on the boards, but I could be mistaken), or something else like Acrylic or Silicone-modified Acrylic?
Does anyone have a capacitor list for other modules like the Steering Column Memory (in the dash?) and Seat Memory Module (under LH seat). both of those modules appear to be acting up and I'm guessing it's also a voltage regulation problem due to old caps. (driver's seat and mirrors move in the reverse direction, the steering column moves out when the turn signal is flipped and doesn't retract when the key is removed. Neither modules holds a memory. I've done the magic reset more than once to no avail).
Thanks in advance,
-Dave

[EEDegreeToDrive]

Any coating should do, a can of conformal coating is usually on the order of $20-30 though, soI suspect there's a lot of people that don't use it (though I have been for the last 100 modules I've repaired);
I think I use acrylic, probably this one: https://www.newark.com/techspray/210...sol/dp/68K7372

The steering column module, door modules, memory seat modules usually use the same/similar 1uf, 10uF, 47uF capacitors as the general module if I recall, though the 1uF seems smaller in the door modules. I've been using multicomp from Newark since they're rated for 105C, though slightly bigger than the often expensive Vishay parts (expensive because they're usually imported from europe). I still use Vishay for the main 470uF cap though, and I replace with Vishay's 105C part. (Vishay's 105C parts for the smaller ones are combined 105/125C, so massive)

The instrument clusters (E32, E34, E31) use a 220uF 40V in addition to the usual 1,10,47,100 I believe.

I've found the easiest thing to do is to disconnect the white cable from steering memory module, this disables the memory function and the auto movement. This reduces the likelihood that the steering wheel gets stuck in a funny position, but preserves manual movement

[m6bigdog]

Just about to get started on re-capping my GM2 (yes, it was cold out yesterday, the windows wouldn't move and the trunk relay was clicking... grrr). Ordering Vishay caps from Newark.
Questions: Are the repairers here using a Urethane conformal coating (which is what it looks like is on the boards, but I could be mistaken), or something else like Acrylic or Silicone-modified Acrylic?
Does anyone have a capacitor list for other modules like the Steering Column Memory (in the dash?) and Seat Memory Module (under LH seat). both of those modules appear to be acting up and I'm guessing it's also a voltage regulation problem due to old caps. (driver's seat and mirrors move in the reverse direction, the steering column moves out when the turn signal is flipped and doesn't retract when the key is removed. Neither modules holds a memory. I've done the magic reset more than once to no avail).
Thanks in advance,
-Dave

I repaired my steering column memory control and the information is in this post #12 & 15 link below:
https://www.bimmerforums.com/forum/s...umn+controller

[DavesNotHere]

Thank you, EEDegreeToDrive and m6bigdog.

I've ordered the Aluminum-electrolytic and Tantalum caps for the GM2, LSM, and EKM, from Newark, and went with the brushable Urethane conformal coating: MG 4223-55ML. (why spray the board when one can just coat the repair? IDK, seems less messy).

LOVE the idea of pulling the White Cable for manual steering column movement only!

Ordered Capacitor list:
105C, low ESR, Aluminum Electrolytic unless otherwise noted.

Qty Value VDC MFR Part# Type

GM2:
(1) 470uf 40v - Vishay MAL213817471E3
(1) 100uf 25v - Vishay MAL202136101E3
(1) 47uf 25v - Vishay MAL202136479E3
(1) 10uf 63v - Vishay MAL202138109E3
(1) 1uf 63v - Vishay MAL202138108E3

LSM:
(1) 100uf 50v - Vishay MAL203690109E3
(1) 47uf 10v - Vishay 199D476X9010D1V1E3 (tantalum, 85C*)
(1) 10uf 50v - AVX TAP106K010SCS (tantalum, ESR: 5ohm, 125C)
(1) 1uf 63v - MultiComp MCRH63V105M5X11

EKM:
(1) 470uf 16v - Nichicon UHE1C471MPD6TD (ESR: 0.32ohm)
(1) 2.2uf 35v - Vishay 199D225X9035B1V1E3 (tantalum, 85C*)
(2) 68uf 6.3v - AVX TAP686K006SCS (tantalum, ESR: 8ohm, 125C)

*1000 hours at 85C. Depending on which distributor parts are ordered from, the temperature rating may appear as -55C to 125C, but this is the operating envelope and not the temperature that the component lifetime is rated at. Just a reminder to look at the VENDOR's data sheet if there's any question as to a part's specification. D'oh!
Tantalum caps are expensive, so unless it's truly a bad idea, I'll use these 85C-rated Vishays (-55C - 125C operating envelope) and see how it goes - anything has to be better than the current "broken" condition.

I probably won't get into the EKM this time around, but the caps will be here. Seat memory module next time around as well. I'll post how it goes in a week or so.

[EEDegreeToDrive]

Some minor points:
1) Spray on coating is nice and quick, and I usually only spray the section of the board I've touched. Not messy at all.

2) To disable the steering wheel memory, it's the white connector, not the white wire.

3) Several of your 'minor' Vishay caps are 85C I think, not really a problem though.

4) I've never done/needed to do an EKM, so might not be worth the risk. If you open it up, you'll see why.

5) On the topic of Tantalum capactors, once there was a single tantalum capacitor that I found shorted in one member's dead EML. Since there's a handful of analog control loops in the EML, rebuilding them might address some strange idling problems, but it's a painful job as it's a complicated split board like the EKM.

I'd worry about your GM, then both door modules before worrying about the others. Misbehaving door modules might not let you in the car/disable the alarm, etc.

[DavesNotHere]

Thank you, EEDegreeToDrive.

I've updated my earlier post with the two 85C tantalum caps ordered in error, as well as a note as to how two 85C capacitors were ordered instead of what looked like 125C caps at first glance.
I have to get the car past the Missouri Safety Inspection before the end of the month. As soon as the GM2 is repaired I'm off to address the failed ABS pump to get rid of the all-too-common dash lights. I have a used spare on hand. I'm guessing a bad brush, since the motor won't spin when the relay is pushed, but who knows? Something will wind up working. It would be nice if it wasn't winter right now... :-D

I'm slowly weaning myself off the alarm. Having one key with what seems to be a bad transponder gets interesting if I lock the doors with the good key and grab the dead key next time I'm out the door... lol
(I've cleaned the contacts and the led lights but the RF output is weak compared to a new key, even with new batteries; the dealer can't get it to pair with the car)

[Timm]

DavesNotHere - a classic reference, makes me laugh just to remember!

[cartoonz]

DavesNotHere - a classic reference, makes me laugh just to remember!

No man.... HE's DAVE! hehe

[DavesNotHere]

heheh...

ZKE (GM2) and LSM re-capped last night and installed this morning. I'll post photos of the work in a separate thread and link to it here shortly.

LSM: https://www.bimmerforums.com/forum/s...ist-commentary
ZKE: TBD

The quick verdict:
It's 28-degrees out and the windows dip and roll-up. No trunk relay-clicking. Looks like at least one ZKE cap was bad, but I did not see anything obvious with a quick check (they do the usual ramp-up on a voltmeter, so at least none were shorted).
The steering column moves as it is supposed to - up when the ignition is off, down when on, no motion when the turn signals are used, goes back to the memory position each time. Same aged capacitor issue it seems. None were obviously shorted. Of course I dropped a plastic LSM nut behind the console somewhere so going to have to dig it out someday. D'oh! Found the top driver and passenger vent motors loose, so that will be another project (and the answer why center-vent heat is hard to come by lately...
Thanks all for your help. Much obliged!

[JaimeLopez]

How to I get in contact with EEDEGREETODRIVE ?
I need to repair my GM.

[Timm]

Send him a PM on this Forum.....

[JV 91E31]

Greetings to all from Ontario, Canada. I have a 1991 850i and began having electrical problems in 2010. I had inoperable door locks and windows at certain times, especially as the weather was getting colder (under 10 deg C.). The worst problem was my trunk release power assist unit which randomly began cycling on and off every 2 seconds, which would drain the battery. Things started getting really bad in the fall of 2020. Fortunately, I was able to find this forum and decided to tackle the General module repair in 2021 after I took the car out of winter storage. I just completed the repair in May and all went well. I thought I would add a few pictures.

When accessing the General module, there is a metal piece that has to be removed which can be seen below the steering column.

Metal piece.jpg

The general module is the middle module in the module blank, seen with the bright yellow connector.
Module Bank.jpg

I took the General Module to an electronics repair store, since I do not have the equipment or experience to solder multi-layer PCB boards. I left the job to the hands of experts. Earlier in May, I ordered the 5 capacitors from Digi-Key Electronics based on one of the earlier entries in this thread. The prices were reasonable and delivery was about one week from MN, USA to Canada. Two of the capacitors were not in stock, but I was able to work with the technical support desk to source alternative capacitors. The alternative capacitors were small and fit nicely into the General Module plastic housing without any issues.

This is what the General Module board looked like before and after the new capacitors were installed. All 5 capacitors were changed. I had all old capacitors checked (after they were removed). There were only two capacitors out of the 5 that failed for capacitance and ESR.

Before (as is, just out of the vehicle)
GM board before.jpg

After (5 capacitors replaced)
GM board after.jpg

I have to say, the repair was a fantastic success. Everything (door locks, window, right rear view mirror slanting down in reverse, trunk lock actuator) is working perfectly again. What a relief to say the least! Lots of peace of mind now.

I want to thank all the people who have contributed to this thread over the years to help find a way to get the electronic gremlins out of the vehicle. It is hard to believe that a couple of old capacitors could create such major issues in the vehicle.

Joe
View of Car .jpg

[sshivaram]

"...There were only two capacitors out of the 5 that failed for capacitance and ESR...." This is good feedback, very detail oriented.

[EEDegreeToDrive]

It's actually not too hard to understand how a few capacitors can cause so much trouble.
The General Module is a microcomputer with the role of controlling/monitoring all the 'consumer electronics'. Microcontrollers/Microcomputers often run several hundred mA when operating, so need to shut down/power off to save energy, but need to be 'wakeable' by things like the doors, locks, etc. They boot up, do some communication check-ins with other modules, and then unlock/turn on lights, etc...The General module 'boots' in about 1-2 seconds... (It's like a 16 or 32MHZ CPU IIRC w/ only a few KB of program ROM and RAM. They also use a 2K serial eeprom for 'coding' different car options, which is only 256 8-bit bytes, and use about half of that for logging faults!)
Anyway, The role of electrolytic filter capacitors is to make sure these modules have a steady power supply in an otherwise 'noisy' environment. A 5V or 3.3V CPU needs a stable power supply, and actuating things like door locks, wiper motors, relay, lights, etc, would cause little brownouts across the car (like when the lights flicker when you turn on the vacuum at home). So, with dried out filter capacitors, the general module boots, then goes to turn on the lights, unlock the doors, etc, and BAM! The Module's 12V supply drops to 10V momentarily, then the 3.3V or 5V bus drops a little bit, and the module either jumps to a random program vector (i.e. 'crashes'), or does a watchdog reset and essentially 'reboots'.
Since the module 'reboots', and never actually finishes 'booting', it never gets back to sleep, and hence you hear click-click every few seconds while it kills your battery at ~500-1000mA. (85AH*2=170AH / 0.75A = 226 hours, ~10 days)
Temperature affects the 'steadiness' of the battery voltage, performance of the capacitors, energy needed to move the 'cold' windows/locks, etc, so this usually rears its ugly head in the winter time.

For reference, in 2021, I charge US-based folks $60 for a module turnaround, including return shipping. It's just enough to make it worth my time, and keep our general module population healthy. As of 6/2021, I think I've done somewhere between 150-200 E31 general modules!

[Exira]

I just brought an E31 last month and run into this issue. I have no experience with soldering or electronic skills and I was able to fix this following the instruction here. Thank you for all the veteran owners. I called up couple BMW shop and they would not work on the E31 and parts unavailability.

[ricks5series]

I too delved into this project and successfully accomplished the repair on my '94 E34 525i. In one of the photos with the arrow pointing to a capacitor, that is the one which controls the start function. If you have a no start during cold weather, it's this capacitor which is not functioning. Warm the capacitor up with a blow dryer, it then works. The only thing I can assume is that the positive terminal separates from the anode foil due to contraction and when heat is applied, it expands and makes contact with the anode. The way I knew it wasn't going to start was turning the ignition switch all the way but not starting the car. The interior lights wouldn't come on but when I heated the capacitor which has the arrow, the interior lights turned on. I then turned the ignition fully to start, and she started. I tested each capacitor, carefully applying heat by placing a soldering iron next to each capacitor and it was the one I've posted with the marked arrow which activate after warming it up.
Btw, this module is located under the rear bench seat behind the driver's side.
Hope all this makes sense.

https://www.dreamstime.com/capacitor...image109089996

The second photo shows all four new capacitors soldered onto the board.IMG_20221217_122519~2.jpgIMG_20221217_122528~2.jpg The bottom photo shows the original capacitors.

[ricks5series]

EEEDegreeToDrive, Great explanation on the purpose of the GM card. I just posted a successful repair before reading your post. I may have shipped it over to you if I saw this before I made the repair. And you're right, this rears it's ugly head during very low temperatures.

[Kylemontanaro]

Are all GM on the 850 the same or do they come in different versions with different capacitors?

[EEDegreeToDrive]

The GMs are physically the same, though later models came with different colored connectors.
However, they are generally coded differently by region, so a "US CODED" module will not have wiper pressure control, headlight washers, and some other options. It's generally an idea to repair/refurbish your own module and put it back in as any 2nd hand module you find might have the wrong coding (and probably 30+ yr old capacitors too)
Likewise, a module that has really "gone to lunch" will sometimes have a bad Serial EEPROM. The EEPROM holds the coding string, but also the most recent N faults, but I believe too many read/write cycles of the module can corrupt/damage the EEPROM, and lead to the coding reverting to European coding, and/or might display scrambled fault logs.