840 SMM repair

[DavesNotHere]

Just a quick post while waiting on capacitors in case I'm headed in the wrong direction here.
I'm planning to post the repair photos once the parts show up.

Since I bought my 6/94 built 840Ci last year, the driver's seat moves usually reversed from the manual switch positions, but not always, the passenger seat moves normally, and the mirrors usually move reversed. On reverse, the passenger mirror tilts up and does not return when the transmission is placed in park or a forward gear. The memory function seems to work correctly. It seems to me that there's a problem with the SMM power supply and not the driver's seat switch, although both could be at issue. There are three Nichicon 105C radial caps in the power supply, a couple of mylar film caps nearby (I didn't trace them out, but since they're film I'm not worried about them), five non-tantalum dipped decoupling capacitors that, IMO, are not likely suspects, and a blue dipped/encapsulated 2-pin doo-dad that I haven't looked into yet (but my gut tells me that it's not a factor since it's on pin 12 (TCMP1 - timer system output compare function 1) of the MPU (Motorola MC68HC05B6, maskset 2C14H). The factory capacitors are marked "HFG", but I can't find that particular series (HF, not FG - "FG" caps are for audiophile equipment). So, I'm ordering what newark has that makes sense to me.

Ordered capacitors:
(3) Nichicon UPW1V221MPD1TD 220uf 35v radial, ESR: 0.17 ohm, 5000 hrs @ 105C

In the meantime, I'm fixing the seat base bowden cables and hopefully the lumbar support. And of course it's freezing out and I noticed that the passenger mirror isn't heating and the passenger washer nozzle leaks under the hood...
But all good, more fun with the bits and bobs.

Stay tuned for photos and the SMM repair work after the parts show up, and please post if I should be doing something different or in addition to this.

P.S. If anyone has an extra SMM case bottom with two good mounting tabs, I'd be interested in it. Mine has one...
Best,
Dave

[shogun]

Any progress with the repair of the SMM?

[Albert850i]

I have noticed that once DIS has woken up the SMM computer, bi-directional communication works fine. However, when approaching another module after that, the SMM does not stop sending messages, disturbing communication with any other module. DIS gives a "communication with head lost" or something error. On a scope I saw that this is caused by the SMM which does not stop talking.
Solution: switch off contact and back on, and the SMM is silent again.
Something wrong with my SMM?

[DavesNotHere]

Just about to dig into it. I got squirrelled with the ASC+T error, replacing the passenger door latch mechanism, and gave myself a SRS light so was trying to get the DIS laptop going sooner than later. To that end, I rebuilt the ABS pump motor on the spare block so I'd have some practice before working on the one on the car. One of the passenger door latch internal springs broke, so I had to replace that with a similar (without the key lever... grrr...) until I can rebuild the original part, and I'm still driving around with an airbag light. D'oh! Anyway, the capacitors are here; I should get to the SMM next week. Thanks for asking, shogun!

- - - Updated - - -

Albert, does your SMM work properly with manual control and with the memory buttons? Have your SMM power supply caps been replaced?

[DavesNotHere]

It's cold and rainy these last weeks and more coming. Working on the DIS/INPA laptop until the weather breaks and hopefully it's smoothish sailing through this Covid-19 thing. I'll get to the SMM caps just as soon as I can. Best wishes to all in the interim.

[Albert850i]

Albert, does your SMM work properly with manual control and with the memory buttons? Have your SMM power supply caps been replaced?

Yes, the seats including memory work fine actually, despite the comms issue. I have not yet replaced the caps, will do so later.

[shogun]

there are more and more reports in the recent years that the SMM module suddenly plays crazy and all goes in reverse. The problem is not wrong wiring, must be electronic parts inside the SMM module.

Apparently also Programa Inc noticed the demand for such repairs, they now offer repairs,
BMW Seat Control Unit, Seat and Mirror Memory Module, OE Part Number 61311388561, ProgRama Part Number 561B, Interchange Part Numbers 3137211012
BMW Seat Control Unit, Seat and Mirror Memory Module, OE Part Number 61311378662, ProgRama Part Number 662B, Interchange Part Numbers 3137211006

In my 11/88 based on ETK p/n is 61351388561 up to production March 1993, Seat, electrically adjustable, front + Memory, 61351388561, Production Dec '89 - , Exchangeable retrospectively vs Old part number 61351378662
Used in E34 , E32 and E31 850 till March 1993, after March 1993 the smaller unit was used 61358356510 , Non exchangeable retrospectively vs Old part number 61351388561