Xiaomi TV Box S 2gen - Add (restore) a working IR receiver

Jul 8th 2024

Xiaomi TV Box S 2nd gen (MDZ-28-AA) is missing what was a feature in older boxes - IR remote receiver. While original remote is using BT, and you likely use HDMI CEC to control the box with TV remote, some may need IR to use with their universal remotes like older Logitech Harmony units that lack BT support Hub provides. Turns out that this box is missing just a few components and there's a full software support for IR included.

Background

Recently I upgraded from a Sony Android TV to Samsung S90C OLED running Tizen. Let's say I hate Tizen for many things, one of them is how Samsung supports controlling devices over HDMI. While there's CEC support (they call it Anynet), they also have "Universal remote" thing that tries hard to identify your device and to control them over IR.

Guess what? Mi Box doesn't have IR. And it is sometimes detected as Orange TV box, sometimes not. When not - HDMI CEC sometimes works, but never fully. I get one of three scenarions: Everything works, everything works except waking up box, nothing works except box going to sleep. Cute.

I use Logitech Harmony remotes. Recently I upgraded to Harmony Ultimate One + Harmony Hub so I can control the box directly via BT - hub is capable of that, it emulates a keyboard and sends proper codes so it works like a native remote.

Sleeping Beauty

It all falls apart though, when you try to wake up the box in any way other than its original remote or HDMI CEC: It simply refuses to do so. It shuts down power to USB ports, becomes unresponsive over WiFi as well as for any other BT devices than its remote.

(Missing) IR remote support

This box doesn't have IR remote support. Marketing materials will tell you about ability to control volume and power of other devices via IR - but that's built in into the original remote, not the box itself. 

I had older Mi Boxes (Mi Box 2s to be exact) that had IR remote support. After looking for TV Box S 2nd gen disassembly photos I found one - and there was a clear footprint for a missing IR receiver visible on the PCB!

Let's add IR back

I took apart oll Mi Box 2S to see if the circuit is somehow similar. In fact it was. After measuring things I decided to move components over to new model and see what happens.

I don't know the model of IR diode. I measured components to be:

  • R211: 100Ω
    • R212: 100Ω
      • R213: 4,7kΩ
        • C229: < 0.1uF
          • C230: < 0.1uF

            Note on capacitors: Those are likely decoupling caps, my multimeter wasn't able to pick the value so they have to be a pretty low ones.

            Anyway, that's how it looks after components are installed:

            But does it work?

            After programming Harmony One with codes for old Mi Box 2S - it worked out of the box. Every single key, including power down...

            ...with a let down

            But of course, it didn't wake up after device went into deep sleep. What was I expecting? Xiaomi really screwed up software of this device.

            A note on (missing) UART

            While I had device aparat I looked for UART port as there's always a chance device could be woken up there. There's a footprint of usual Xiaomi port (J1200) , but upon closer examination - multiple passive components on both sides are missing. With oscilloscope I found some activity on CPU-side leg of missing Q802, but that was definitely just some random messages once in a few seconds, not a boot log - thus I didn't investigate it further.