Logitech M570 Teardown and Repair

February 28, 2014 Kenny Millar Electronics, Hardware, Mac, Teardown, 19

The Logitech M570 is one of very few thumb-operated trackballs on the market. For anyone, like me, who suffers from RSI in the wrist, it is an ideal replacement for a mouse as it removes all the moving back and forth – your wrist stays in one position and does not move when using it.

I have had several of these over the years and they have all suffered from the same problem: after just a few weeks of using them, they start to develop problems like double-clicking and dropping files when you are trying to drag. I posted a blog about this earlier. You can read it here.

In this post we will teardown the M570 and repair the cause of the problem.

Tear down of the Logitech M570

To open the trackball first remove all the major external removable parts: The ball; battery cover and micro-receiver if it is still hiding inside the battery compartment.

Next remove three of the small rubber pads – they cover some of the case screws. They can be easily lifted out and if you are careful you can put them back again later without any damage. You don’t need to remove the pad nearest the ball hole, there is no screw hiding under there.

Now remove the 5 case screws, one from under each of the pads you removed, and one near the ball hole. There is one more screw to find, and it hides under the battery compartment label. Gently feel for the screw hole under the lable using the tip of the screwdriver, you’ll find it right below the ‘5’ where it says “1.5V AA”. I guess this is Logitech’s attempt at detecting tampering with the device since you have to damage or remove the label to get to the 5th case screw.

With all the screws removed the two case halves just pull apart, there are no catches or lugs. Looking at the case you can see a lot of design and engineering has gone into producing this device. It’s a shame it is let down by the small problem that it becomes unusable after just a few weeks! (Your mileage my vary, I use mine all day every day).

With the case separated we can see that this trackball uses a single board, and an optical image sensor for tracking the ball movements. It uses two sub-minature microswitches for the left and right buttons and two board mounted captive tactile switches for the auxiliary buttons.

By removing 4 more screws you can remove the entire circuit board complete.  Look out for the one just below the two auxiliary switches it is easy to miss. The circuit board lifts out when you gently pull the battery contacts out from the guides. Once you lift out the PCB be careful not to lose the tiny plastic switch cover that forms the ON/OFF switch. It will be lying in it’s position in the lower case just waiting to drop out onto the floor, never to be seen again.

That’s all there is to it, a nice design, easy to disassemble and easy to reassemble. In the time honoured fashion: Reassembly is the reverse of the disassembly procedure.  When re-assembling be careful to align the on-off switch with the tiny slide switch on the bottom of the PCB, so that it is in the correct position for operating the switch once it’s all put back together. Click the thumbnail above to see all the components laid out.

Investigating the problem.

There are many reports of this problem with these trackballs, the reviews on sites such as Amazon almost always mention it.

Originally I thought the cause of the problem was probably cheap microswitches with a horrible debounce pattern. To check this I hooked up my oscilloscope to the buttons inside the device, and compared their debounce patterns to some high quality C&K switches from digi-key. As it turned out the debounce patterns were almost identical without too much noise at all. Anyway that wouldn’t explain why it was becoming impossible to drag with the trackball – it was like the button was letting go.  So I compared the buttons in the trackball with the C&K ones from DigiKey. They measured exactly the same physical dimensions, and had identical characteristics with two minor differences:

1. The operating pressure required to operate the switch was slightly lower with the factory fitted switches.
2. The factory switches went open circuit almost as soon as you started to release any pressure, whereas the C&K Switches didn’t go open till you had released almost all the pressure.

This second point turned out to be the cause of the failures: The switches were making contact when pressed, but releasing with almost unnoticeable reduction in pressure – so when you were trying to click, the natural movement of your finger was causing multiple clicks, and the same when dragging  – the natural variation in pressure from your finger was enough to let the switch contacts open and close repeatedly, thus ruining your drag operation.

I purchased a bunch of replacement switches from DigiKey – they are DigiKey part number: 401-1742-ND, and C&K Manufacturer part number: ZMCJF7P0T.

I have had several of these trackballs over the years. The earliest ones used some cheap looking unbranded switches, but the latest ones used genuine OMRON switches, but they all suffered the same fault. I think the real problem here is that Logitech just specified a switch with with too low an operating pressure, probably in order to make the buttons feel easier to use.

Repairing the trackball

With the device disassembled, remove all the solder from the three pins on each of the microswitches. I simply used a soldering iron at 385℃ and some 2.5mm solder wick. If you can’t get the pins cleared then you could try using some ChipQuik.

This picture shows a comparison of the factory Omron switches (top two) with the C&K Switches I purchased. (lower two, with white bases). Click the image for a larger view. They are pretty much identical in terms of physical dimensions, but the C&K ones have a much more positive click and feel to them. The actuator might be just a smidgeon higher, but’s hard to see.

Solder the two new switches in place, and clean up any solder flux residue with some IPA and the jobs done. Here’s a picture of the board with the two new switches soldered in place. Re-assemble the trackball using the reverse of the procedure for tearing it down and Bob’s your auntie’s husband significant other.

So that’s it for the repair of the Logitech M570 Trackball. Having put it all back together and put the batteries back in I’m delighted with the results, no more double-clicking when it shouldn’t and I can drag and drop without hitch, and the switches have a nice positive feel to them, they are not too heavy to operate at all and have lovely haptic feedback. I would say they feel, sound and work better than they did when brand new out the box.

All in all the total cost of repairing the trackball was less then 3.50 GBP ($5.00). I bought 10 of these switches from DigiKey, and have used 4 repairing my two M570’s. So I have six left over if anyone needs a repair doing….

Take care.
-Kenny.

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