Replacing SI batteries not difficult (very LONG) (archive)

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If you can use a soldering iron and have a steady hand and patience, you can do it. For what it's worth here's my experience this last week...

Our oil service light wouldn't reset, so on a hunch I decided to replace the batteries on the service interval board in Kate's bimmer (a 1985 735i). I used 700mAh batteries (with solder tabs) that I purchased online at www.radioshack.com (part # 23-191 - package of two). And I used advice and encouragement received earlier from very helpful members of this board.

Note: before proceeding with the battery replacement, I gently cleaned all the boards and contacts with contact cleaner, then with DeOxit and a soft toothbrush, then lubricated all terminal connections with DeOxit.

Then I examined the boards using a magnifying glass (with its handle secured in my vise). I was looking for potential damage. I'm no electronic master by any stretch of the imagination, so I was just trying to look for something obvious... I did find some areas where the soldered contacts or board "tracks" looked kinda dark or slightly corroded. However, none of the track lengths seemed bad enough to consider bypassing them with soldered wiring. To prevent further deterioration I just applied some DeOxit to suspect areas. It seems that I use a lot of that DeOxit stuff, but the level in my little bottle hardly ever seems to go down -- amazing. A little goes a long way, especially using that handing long metal tube that comes with it.

Fyi, a person called "Amber" also gives some battery-replacement advice at www.bimmer.org/e23/messages/archive/msgsy2001w30/11800.html

I didn't follow Amber's approach, exactly, because I chose to desolder the old battery tabs from the board entirely, then solder 2" wires into those board locations (I just found that it was easier and cleaner for me to solder wires to tabbed batteries).

Note: I found it helpful to have a "solder sucker" to remove most of the residual solder from the board prior to installing the wires.

Then I simply soldered the wires from the board to the appropriate (+ or -) tabs on the new batteries checking for good contact using both the "pull" test and a check for continuity with my trusty ohmmeter. I covered the soldered battery tabs with short lengths of electrical tape after applying some DeOxit to inhibit corrosion. Laid the wires along side the batteries and situated the batteries where I wanted them on the board. Then I squished some "clear" silicone between the two batteries, slightly separating them with my fingers to allow some of the silicone to flow down, around, and underneath the batteries. Then I pushed the batteries back together, wiped off some of the excess silicone, and let the board sit overnight to allow the silicone to set (it goes on white, then turns clear with time..).

Next day I carefully reassembled the instrument panel, reinstalled it into Kate's 735i, and everything worked just fine - performed the SI reset successfully this time! 8-)

I sure hope these ramblings from an old retired nuclear engineer don't bore you too much, and maybe they'll give you some confidence to proceed, if you ever needed that in the first place... Hey, if I can do this task, anyone can! LOL

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PS: Here's some additional cautions and hints that may help you get through the process...

-place a towel under the area of the instrument panel face where the odometer reset button is located to prevent possibly damaging the button or cracking the face

-you can magnetize your screwdrivers if you wish using a magnet on backside of an old speaker. Lay the screwdriver on the magnet and pull it toward you repeating this process several times, then strike the screwdriver hard against a solid object (like a vice) and repeat entire process once more (or until you achieve the degree of magnetism on your screwdriver that you want).

-Note: be careful not to get your magnetic screwdrivers near any electronic component that may have some form of stored memory (like ROMs, EPROMs, etc.). I'm not sure if the SI computer has this attribute or not, but I try to avoid anything that looks like a computer chip, just to make sure...

-be careful when removing and storing the speedometer, tachometer, and fuel/temp gauge units -- their gauge indicator "hands" are very fragile and can bend or break pretty easily... take your time and protect these delicate instruments -- cover them carefully after cleaning the contacts, so they're not exposed to dust, smoke, or other contaminants. Note: if you happen to break one of the hands, don't you get bent out of shape, too. You can easily repair them using JB Weld, then "re-color" 'em white after the JB weld has dried with some of that white typewriter correction fluid we older guys once used back in the good ole days... 8-)

-now use this opportunity to check all the bulbs on the board -- they should all have continuity when checked with an ohmmeter (I just used a volt/amp/ohmmeter I bought from harborfreight.com for about $7). If the bulbs don't show continuity, then replace them.

-If any of those tiny bulbs on the transmission shift-location indicator board need replacing, I found it wasn't that hard to desolder the bad ones and resolder new ones. However, removing the board from the plastic mounting tray was a bit tricky. Had to "soften" the plastic hold-down columns first with my soldering iron while carefully prying upwards with a knife inserted between the plastic and the board. When I needed to reattach the board to the plastic, I then simply (and carefully) snapped the board back over the plastic columns and carefully pushed any gaps together with needle nose pliers -- fit wasn't as tight as it was before the softening operation, but, hey -- good enough for the price! 8-)

-I found it helpful to mark the locations on the SI board of the + and - terminals for the ni-cad battery with a marker pen, so I wouldn't forget which holes in the board went with which polarity on the batteries.

-For each battery location there's one hole on the board for the positive terminal and two holes for the negative terminal. However, each battery I purchased only had one tab on each end with a small hole through each tab. I know I could have just soldered a "jumper" wire between the two negative holes, but for some reason (?) I chose to solder a separate wire to each hole on the board (red for positive and black for negative). That meant I had one wire to connect from the board to the positive end of each battery, but two wires to connect to the negative end. So I just twisted the two negative wires together and inserted them into that single hole on the negative tab of the battery terminal and then bent the wires back toward the insulation to form a nice tight loop. Heated the loop/tab intersection with my soldering iron and then melted some solder onto that juncture until I had a sufficient quantity (not a big glob, however). I liked using wires instead of keeping the old tabs. Because I cut them about 2" long, I had plenty of room to do the soldering to the batteries and also could bend them to get them out of the way once it came time to silicone the batteries to the board. That just worked well for me... your mileage may vary. [NOTE: it probably makes more sense (if I can just remember next time) to jumper the negative terminals, as I indicated, rather than use two wires from each of the negative board locations.]

-when putting the SI board back into the panel I found it easier for me to connect the "top" terminal of the board to the corresponding ribbon connector prior to inserting the combination and screwing in the three hold-down screws. Note: you can insert those screws into the board prior to lowering it into the panel or use a magnetized screwdriver -- makes it easier to get them in those little tiny holes if you have big fingers like mine... Then I pulled the other ribbon connector up until it had no slack, and this allowed me to get the connector started on the other terminal, lowering the pieces together while firmly and carefully pushing connectors together from the side access location. Note: make sure you apply the force in line with the terminals. These connectors are plastic and a horizontal force can cause them to break (don't ask me how I know...LOL).

-don't tighten the screws too hard -- they're metal and screwing into plastic can break or strip the plastic if you're not careful.. (again, don't ask me how I know...)

--
Rick & Kate Johnson
Venice Ranch, Burns, Oregon
home.centurytel.net/venice/
1985 BMW 735i (Wife's); '85 BMW 745i (Son's); '89 Cherokee (Mine)
www.gilgordon.com/telecommutesafe/thoughts.html

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