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Fixing your SCX Digital chip: Part 2 (Replacing the reed switch)

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  • Fixing your SCX Digital chip: Part 2 (Replacing the reed switch)

    This posting was originally from the SCX Worldwide site.

    Fixing your SCX Digital chip: Part 2

    Replacing a broken reed switch

    Allright.... time for the ubiquitous disclaimer.

    Disclaimer: What you are about to read is in no way implying that everyone should be expected to repair their own digital chip. This is merely a guide for those curious enough and comfortable w/ electronics to explore at their own will. In addition, because SCX does have a two year warranty on everything they make, always contact SCX for warranty coverage on a damaged chip.

    Now it's time for the fun part. ^_^

    This topic is in regards to replacing the reed switch on digital chips. The purpose of the reed switch is to register the cars as they cross the finish line to enable lap counting and chronometer readings so you know where the car is @ all times during a race in relation to the other cars on the track. And of course, it helps the system decide who wins and loses by the end of the race. Without the reed switches working properly, you will find your car never registering laps or chrono readings. There are also reed switches located in the start/finish track as well as the pit entry track to complete the cycle of this lap counting system but this topic will only cover the units in the cars.

    To start off, let's identify what a reed switch looks like and where they are located on both types of SCX chips. Here is a picture of both types of chips.

    If you notice closely, the F1 chips incorporates a metal shield that the V1/V2 chip lacks. I am not 100% certain of the purpose for the cover but I assume it has something to do w/ reducing magnetic field emmissions from the F1 motor (since the standard chip has its reed switch closer to the front of the car, it's farther away from the motor and doesn't need a shield).

    Now here is a picture of what to look for in a bad reed switch.

    As you can see, there is a crack in the glass that encases the two metal switches inside. Now that air has penetrated what is supposed to be a hermetic seal (air tight), this switch is now totally useless. Even if you were to attempt a repair by trying to re-seal it, it's still useless since air has already gotten in. The only recourse is to replace it.

    With the help of Brian @ BRS and timo, I chose the RI-25AA reed switches (unit cost 90 cents each for a quantity of 10) that are available @ Digikey. Here is the link in case anyone is interested in ordering these for themselves.

    Here is also a picture of how these reed switches look in the raw next to one already in place on a digital chip.

    Time to make the repair.

    Unlike what I had described in my earlier post regarding the replacement of a transistor, I won't go into extreme details on how to remove and replace the switch. And the reason why; it was easier to remove a reed switch vs the transistor.

    For removal, simply heat up the solder on the both ends of the old reed switch and hold the chip on an angle. Because the switch is already damaged, it will simply fall off the chip once the solder liquifies. That's it. Very simple.

    For installation, align the new reed switch in the exact position the old one was in and make sure that the metal switches in the reed are positioned w/ the "flat ends" facing up and down (not back to front) and solder to the points on the board. Also, make sure that the switch touches the surface of the chip (otherwise the metal plate on the F1 chip will not fit over it later). See the pics below as a reference.

    and of course cut the remaining ends of the new reed switch off since they are not needed anymore.

    Re-installing the chip in the car (F1 version only).

    Now that the new reed is in place, we need to re-install the chip into the F1 car. I wouldn't make such a big deal about this procedure if we were dealing with a V1/V2 chip but I feel a need to really emphasize some issues I have w/ the F1 version.

    First off, make sure you install the metal plate again over the reed switch as shown below.

    The larger side of this plate should be on the bottom and the plate needs to hug the switch closely. However, be very gentle when pushing the plate on because I did break a new switch as I tried to install it. (I'm not really that sad since it was 90 cents.)

    When installing the chip back into the car, also be very careful to not bend the chip in anyway or you will also increase the chance of damaging the reed as well. In order to get this chip in w/ minimal fuss, place the front end in first and then gently bend the plastic chassis downwards (around midpoint) to gently get it under the rear locking tab. Below is a pic on how the chip should look afterwards in the chassis.

    So that's essentially it. I repaired two of my chips that had bad reeds (both F1) and tested accordingly. They both work great now.

    As an FYI, I do want to emphasize that the reeds on these chips don't go bad very often. On all my cars utilzing the V1/V2 chip, none of them has ever had a problem w/ bad reed switches. All of the issues have been the F1 cars and after awhile I figured out why. It's as simple as this..... "Don't take them completely apart unless you absolutely need to." I was trying to be very detailed oriented on my maintainance routines and over time the procedure of constantly removing and installing the F1 chip flexed the area of the reed switch so much that eventually it just cracked. So from now on, the most I'm going to do is take the body off and just oil and grease up the gears w/ everything in place (that's really all one needs to do anyway). The chip stays in the car from now on and that's that.

    Once again, I hope some of you found this information useful for your own needs. And if not, at least you know what to look for if you have a problem w/ your car.

    Now I gotta get some sleep. :shock:


    Last edited by LDFan; 10-28-2012, 11:57 PM.