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Repairing Atari 2600 Original Wireless Controllers

So, I've recently been repairing a large selection of Atari paraphenalia and, included in the container-load, was an official Atari-branded CX-42 wireless controller kit! The setup is pretty awesome; the base unit has a power input and then an output to go to the console. This means it doesn't need a separate power adapter as it chains into the power for your Atari. It then has the two controller plugs which you simply insert into the left and right controller ports on your console. Finally, the joysticks are more-or-less standard one-button Atari joysticks with extra 4cm bases to contain a 9v battery and radio circuitry.


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Of course, this came to me due to being unhealthy. One of the controllers wouldn't go left! I'd usually associate this to cable failure, but... well... they don't really get much abuse in this scenario! They needed a good clean anyway, so the tear-down and diagnosis begun.

Is it the controller? (Hard way!)

So, just because I'd previously torn 100s of these apart, I went straight to the controller to check the internal switches. The construction of these is relatively simple, until you try to separate the joystick circuit board from the actual joystick... so many screws and springs fly everywhere. Regardless, once the unit was open, all switches were tested and found to be functional. I didn't think of taking a photo at the time, so you'll just have to imagine.

Is it the controller? (Easy way!)

After a little googlin', I stumbled across this hint stating that you could 'hear' the controllers using an FM radio. Hah, of course you can... It seems that they use frequencies down around ~40mhz, but somehow you can hear this at ~100mhz on your FM radio. So, what to do? Find an FM radio first. Fortunately I had some on the shelf thanks to wanting to listen to tapes a few months back.

On Windows 10, you'll find there's no more sndrec32. Instead you need to browse over here and Voice Recorder. Yey for anti-monopolistic effort! Anyway, I managed to record the following:

What you'll hear above is: Static -> radio station -> static -> radio station -> static -> weak carrier signal! -> misc. tuning -> STRONG CARRIER SIGNAL! -> 5 presses of the fire button -> ~7 full rotations of the joystick -> 6 presses of the fire button (the last one is longer) -> static. Totally random! But it's a great way to test.

As you can hear above, I started just above ~102mhz FM and scrolled down until I found the carrier signal. Note that I had difficulty originally finding the signal as it's not that strong. Make sure you hold the joystick against whatever FM receiver you're using.

Once the carrier signal was found, I then fine-tuned it until the signal was the strongest and began mashing buttons. Of course, just because LEFT is transmitting something, doesn't mean it's transmitting the correct signal! But hey, we can now check the base to see if there's any obvious issue.

Is it the base unit?

The circuitry inside this unit is, thankfully, quite easy to trace and diagnose. The unit consists of two individual circuits, decoding each controller independently. This is actually a life-saver, thanks to one of the joysticks being 100% functional! With my multimeter in-hand, I went ahead reviewing the circuit and measuring signals along the way. Doing this for both joysticks and both circuits meant that it was straight-forward to determine where the signal started going funny!


Starting from the output, there are two hex-inverter chips on each side. All 6 inverters (2chips x 3inverters) on each side are used and these flip the signal before sending it out to the controller port. The left button was seeing a twitch in the voltage, but not enough to flip the inverter to full +5v. The input was meant to drag to ground, sending the full signal out, but it wasn't happening.

Tracing the signal back, there is an OKI MSM4015RS IC and, for the life of me, I still can't find a datasheet online. I thought this would be a show-stopper, but after testing the signals on this IC for both joysticks when the fire button was pressed, it turns out they're both reporting the same values.

I therefore traced the value back up towards the output and found that the output after the first inverter wasn't being dragged low enough. It was 0.6v on the working joystick and 0.7v on the failing joystick. The output of the inverter is tied to ground with a green-cap and tied high with a 4.7k resistor.

The resistor checked out, but I had no way to test the capacitor with my multimeter. Instead, I swapped the capacitor from joystick one's side to joystick two's. Surprisingly, this now saw joystick one's LEFT button working and joystick two's was now faulty. Nice!

Replacing all green-caps

You'll find three different-valued sets of green-caps on this board: 10x 183k100v (18nf), 10x 223k100v (or 2A223K) (22nf) and 6x 104k100v (100nf). I went ahead and purchased a full set of them from Jaycar with the goal to replace every one of them.


Who knows how close another is to frying?


The aftermath... (did I say only the green-caps? Ooops.. I didn't discriminate and took out the electros as well.)


Removing and replacing was easy enough. I really recommend Goot-Wick desoldering braid for cleaning up the PCB whilst you're doing things like this.

Now up doesn't work?

Hah, seems that enough plugging-and-un-plugging of the controller output cables from the main board caused one pin to fail. Thanks to standard technology, there were plenty of these plugs in my junk box, although not with the same pin count...


So I borrowed an internal connector from a three-pin plug and soldered it in. Worked perfectly!

A minor note on the usage of these wireless controllers

With the wireless base unit powered-on and fully-connected to your Atari, it'll send spurious/erratic/totally-crazy signals to the console on the joystick cable of any joystick that is turned off! There is therefore a correct sequence for powering everything up... Turn the joysticks on first and then the base unit. Note that the base unit doesn't have a power switch, so I'd recommend always turning it off at the wall. I suppose you could then leave the Atari power switch on, as you'll be using the wall switch as the power cable is chained through the wireless controller receiver. Just make sure that both controllers are powered on BEFORE you turn on the wall switch!

When I was first diagnosing this kit, I thought all was pointless after seeing the random signals coming out of the base unit. I was very happy to see the signals settle once the joysticks were powered up!


This unit worked splendidly with 2600-series consoles and games.


Even 2600 games in a 7800 console. What didn't work was the built-in asteroids for/on the 7800.


For some reason, the down and fire buttons won't work. Of course, a standard 1-button Atari 2600 joystick works fine on 7800-Asteroids, but this unit doesn't. I did a little digging and found that the pins aren't brought straight to ground... instead they hover around 150-250 ohms... I wonder if that's enough to not send through a proper button press? Also, they seem to 'repeat'... the multimeter actually goes pretty damn crazy when a button is pressed, beeping on and off as the resistance floats near-zero. As mentioned above, each output is tied high by a 4.7k resistor and low by a 22nf green-cap capacitor. I assume the cap is there to de-bounce the incoming signal, but maybe it's not big enough to trigger a single press for the 7800? I don't want to modify this unit as it's very original, so I'll just suggest that if anyone else wants to use this on a 7800 then they should tinker with the pull-down capacitors on the output lines.

Again, they worked 100% perfectly with all 2600-series equipment I tested.

Battery Cover

One was missing, so I used my Creality CR6-SE to bring a replacement. It didn't turn out toooooo bad. Works well when there's a battery inside... falls out when there's no battery!

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