What type of zener diode is this? The thin band is blue.enter image description here

  • \$\begingroup\$ MELF packageing, possibly glass-body \$\endgroup\$ – JonRB Jun 27 '15 at 15:05

Other than the package looks like LL34, it's impossible to tell from the picture. The wide yellow band is almost certainly marking the cathode end. The line in the middle is not a marking band, but a artifact of construction.

You can try measuring the voltage across these diodes in normal operation. Keep in mind that for a Zener diode in Zener mode, the cathode is positive. If these are used as voltage references, that may work. If they are for clamping or other intermittent purpose, you may get lucky looking at the waveform over time. Otherwise, remove the didoes from the board and see what voltage they develop with about 1 mA reverse current.

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