Components on PCBs are usually labelled using silkscreen markings and most of the markings seem to be quite intuitive:

  • C?? - capacitor
  • D?? - diode
  • FB?? - ferrite bead
  • J?? - jumper wire
  • L?? - inductor
  • LED?? - light emitting diode
  • Q?? - transistor
  • R?? - resistor
  • RJ?? - RJxx connectors
  • SW?? - switch
  • T?? - magnetics (ex. for RJ45 connectors)
  • TP?? - testpoint
  • U?? - packaged integrated circuit

What could be the component marked as 'Y??' be? Unfortunately the board where I have this marking does not have this place populated.

[Edit] Wikipedia has a page about reference designators.

  • 4
    \$\begingroup\$ en.wikipedia.org/wiki/Electronic_symbol#Reference_designations \$\endgroup\$
    – starblue
    Jul 13, 2011 at 20:53
  • \$\begingroup\$ @starblue, I guess we have a winner \o/ \$\endgroup\$
    – plaes
    Jul 13, 2011 at 20:57
  • \$\begingroup\$ What is it connected to ? \$\endgroup\$
    – endolith
    Jul 13, 2011 at 21:21
  • 1
    \$\begingroup\$ J is also used for connectors. \$\endgroup\$
    – stevenvh
    Jul 14, 2011 at 4:24
  • \$\begingroup\$ @stevenvh yes I thought it was J for Jack and P for plug. Updated: nice link from @starblue. \$\endgroup\$
    – kenny
    Jul 14, 2011 at 5:04

2 Answers 2


Y?? or X?? could both be a crystal or oscillator. Unfortunately there is no standard for this type of thing. If you posted a picture of the footprint we could take a better guess.

Also: Q=Transistor. RN=Resistor Network.

  • \$\begingroup\$ Footprint is 2 + 2 pins (square), so it cannot be crystal. Thanks for improving my list :) \$\endgroup\$
    – plaes
    Jul 13, 2011 at 20:50
  • 1
    \$\begingroup\$ @plaes, not necessarily. Some crystals packages have 4 leads, even though crystals are only two-terminal devices. Square would be a bit unusual though. Still, I agree with David in that it's most likely a crystal. To really know, you'd have to check the BOM (Bill of Materials). \$\endgroup\$ Jul 13, 2011 at 20:53
  • \$\begingroup\$ @Olin, getting access to BOM is a bit hard, because the PCB is from TP-Link router ;) \$\endgroup\$
    – plaes
    Jul 13, 2011 at 20:56
  • 1
    \$\begingroup\$ It could be a crystal oscillator module such as one of these Euroquartz modules. \$\endgroup\$
    – MikeJ-UK
    Jul 13, 2011 at 22:30
  • 2
    \$\begingroup\$ A great many SMD crystals are 4-pin devices! Digikey reports about 3000 in stock, and they're standard on everything we build at work. The oblong tin can with two through-hole connections is not the only type of crystal. \$\endgroup\$ Jul 14, 2011 at 0:14

I have seen Y used to label crystals and oscillators. This is how OrCAD labeled their library parts.


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