Logicon Repair

From: "Tsai, Mark" mtsai@foci.com
Date: Thu, 08 Aug 96 19:17:28
Subject: [2] Logicon Repair/Replacement

Hi Folks: I've seen a couple of requests go by for this information, and I'm not sure if its in the FAQ or not, but I thought I'd write down my experiences (and the problems I ran into) while fixing my logicon. I've also done the little kick-panel module (to fix broken horn, random seat-belt light, etc.) and the idiot-light/clock module (to fix flickering/no clock), so if there's any call for these, I can do up a similar writeup. (I figure its time to give something back to the list which has provided me so much information, and more than a few chuckles. :) To whoever is maintaining the 2nd generation FAQ, please feel free to add this if you think it meets your quality standards.

For reference purposes, I did this replacement on an '87 base, so if they changed the color of some of the plastic, then don't sue me. :) In addition, although I'm trying to be as helpful as possible with the following information, I'm take no responsibility for any errors, omissions, or if you melt down your car with these instructions. :) I'm writing this from memory, so there may be some errors. Please correct me if my memory fails.

Logicon Resoldering/Replacement

Symptoms

Ducts do not redirect airflow when different positions are selected (i.e. Defrost, Flow towards feet, Flow towards face etc.) Fan does not respond to fan-speed control, or full range of speeds not available. Temperature slider does not adjust the mixture of warm/cold air

Solution

Resolder 'cold' solder joints within modules/replace parts

• Step 1: Expose module On either side of the shifter boot, where the black plastic meets the YIC (your interior color) plastic, insert a THIN screwdriver, gently work it up underneath the black plastic. This should pop each side free. This is a great opportunity to clean out all the junk which accumulates in the crevices in the shifter boot. :) This will uncover two screws just behind the ashtray. Remove these, putting them in a safe place. Now, remove the ashtray, and remove the two screws under the ashtray. Put them in a safe place. The tricky part: Insert something wide and flat between the two heater vents, and the black frame surrounding them. CAREFULLY pry the heater vents away from the console, and they will pop out. This may take a bit of pry here, move a few centimeters, pry again, etc. There are two screws behind the top of the frame which must be removed to successfully remove the frame intact. (This was not mentioned to me, and now I have a cracked frame. I've seen quite a few of these broken, as these screws are not exactly in an obvious place.) This should leave you with a total of 6 screws in your 'safe place,' and a pair of heater vents, and an ashtray. At this point the frame should lift off of the console, exposing the radio, and logicon.
• Step 2: Remove module Four gold screws hold the logicon into console. Remove these, and the console should slide forward a few inches. Again, be very careful, as there are 2 cables coming out of the back of the logicon. One of these is plugged into the back of the logicon, and one will appear to just go into the guts of the logicon. The plugged-in cable is shorter, and can be removed just like any other harness on the car, i.e. by pressing the little tab down and pulling back on the connector. The other cable which disappears into the box is tied onto the beige box via a zip-tie. Cutting this may give you a little bit more room, as the following steps have to happen with the box attached to the console via this cable. (N.B. It IS theoretically possible to find the other end of this connector in the dashboard and detach it, but after I screwed around for a while trying to find where it was attached, I gave up and just lived with it. I found it wasn't bad working this way, and keep in mind that if you DO detach it, you'll later need to reattach it!)
• Step 3: Inspect logicon This isn't really a step, but it helps for us to have an understanding of what I am talking about for the rest of this document. The logicon is made up of 3 discrete modules. There's the faceplate, approximately 1.5 inches deep, containing the slider controls, etc., a small (black) box, and a larger beige one. The black box detaches from the beige one with a single screw, and the faceplate detaches from the beige part with 4 screws, one at each corner. Now, what happens next depends on your symptoms. I found that resoldering the large solder points fixes problems >60% of the time, however, I haven't actually opened the faceplate yet to inspect the fan potentiometer, for instance. When my logicon failed for the third time, I just bought another one from a junkyard. The Mazda dealer wanted more than $400 for it! It cost $75 from a junkyard.

To resolder the solder joints

• Step 1: Separate 3 parts of logicon Separate the black box from the beige box by removing the single screw in the back holding it on (this step isn't strictly necessary, but I found it much easier to deal with the beige unit when separated from the little black box.) Separate the beige box from the faceplate by removing the 4 screws in each of the corners. This will reveal the circuit board inside the beige box. The faceplate will be attached by a wire harness, and the little black box will be attached by another wire harness.
• Step 2: Remove the circuit board from the beige box There are two small plastic retaining clip which holds the circuit board inside the beige box. Sliding a screwdriver underneath one and then the other will release the circuit board. Slide it forward. The solder joints you are interested in are on the underside of the circuit board.
• Step 3: Resolder the joints Usually, the bad solder joints are the ones connecting the long, flat wire harnesses to the PCB (printed circuit board), but it's not a bad idea to go ahead and resolder any of the large solder connections. I didn't have the patience to resolder them ALL, but I did do most of them. Make sure that your solder joints are nice and shiny (i.e. heat the metal, not the solder, etc.), otherwise you'll be doing this all again in the near future! Slide it back into the beige box when you're done. I don't want to turn this into a tutorial on soldering, but all of the standard soldering caveats apply, use the right powered iron, good ELECTRICAL solder, etc.
• Step 4: Assembly is the reverse of installation Don't you hate when they say that? Just make sure that you don't overtighten the screws in the frame, as this piece of plastic is very brittle and will not respond well to overstressing.

Replacement

To replace the logicon, use the instructions above to remove it, however you'll need to either find the end of the wire harness which is buried deep within your dashboard, or alternately do what I did, which is desolder the end of the cable which is attached to the PCB, and resolder the cable to your new unit. - Mark