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I disassembled an iPod Nano 2 yesterday and was surprised to find a round brass-coloured plate glued to the back. I didn't find any mention of it at the teardown over at ifixit.com, as they didn't cut the case in half. The back of the logic board has two contacts pressed against this plate.

Since it just seems to be a piece of metal connected to the case and is quite discoloured, I'm reminded of galvanic anodes attached to chips to protect them from corroding. Does anyone know why this plate is there?

I'm a physics teacher and this seems like an opportunity to teach my students something.

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  • $\begingroup$ Possibly a simple master switch so it only works with the case closed... $\endgroup$
    – Solar Mike
    Mar 21, 2021 at 13:01
  • $\begingroup$ stability conductor, they had some extra metal to use. idk. good question. $\endgroup$
    – Dane Hart
    Mar 22, 2021 at 3:12

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It's a naked piezoelectric buzzer.

Some piezoelectric crystal grown on a metal circle are the active part and the bottom contact glued on the back cover.

The top is then metallised to get the second contact.

Wires could be soldered to the contacts and/or the device could be cased in some plastic box but, since space is a premium here, it's used as is without case and the two spring loaded contacts on the PCB drive the buzzer.

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  • $\begingroup$ This was my first thought, too, but I don't remember these ever buzzing? $\endgroup$
    – Jonathan R Swift
    Mar 21, 2021 at 17:17
  • $\begingroup$ It's s good point, but it really looks like that so much that I can't imagine anything else. It may play like a small low-fi speaker or it could be a dropped feature. I've never owned an iPod though, no clues. $\endgroup$
    – carloc
    Mar 21, 2021 at 17:38
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    $\begingroup$ Update: they did apparently beep when in an error state! (Mine never broke which explains why I never heard a beep) fixya.com/support/t4006646-white_screen_ipod_2_beeps_restart $\endgroup$
    – Jonathan R Swift
    Mar 21, 2021 at 17:42
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    $\begingroup$ Could it have been used to provide the clicking sound for the clickwheel? $\endgroup$
    – Wes Toleman
    Mar 22, 2021 at 0:38
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    $\begingroup$ @WesToleman Yes, definitely yes $\endgroup$
    – carloc
    Mar 22, 2021 at 1:01
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To enlarge upon carloc's answer, you can actually see the contact studs for making connection to the piezo disc in the lower image. they are the gold-plated spring doots in the little green PC board.

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