I am organizing a bunch of components given to me; some of them not put in a labeled bag.

This SMB diode has the marking "1042 MZ" on it and I cannot find any references to this. And I have checked a SMD Code book without finding anything.

I am running out of good ideas :)

Unknown diode

Edit: Applying 1V in forward direction made it hot and conduct 2A. Slowly increasing the reverse bias voltage with an LED in series confirmed that it is a unidirectional TVS diode starting to conduct at about 70 volts.

  • \$\begingroup\$ Do you have enough to be able to do some destructive tests to figure out what you have? \$\endgroup\$
    – The Photon
    Nov 22, 2019 at 19:37
  • \$\begingroup\$ Yes, I got a hundred pieces (therefore a shame just to discard them). So I could easily let one release its magic smoke. \$\endgroup\$ Nov 22, 2019 at 19:48
  • \$\begingroup\$ It blocks in reverse direction up to the 60V my power supply can deliver. Applying 1 volt in the forward direction it conducts 2A and of course gets smoking HOT. \$\endgroup\$ Nov 22, 2019 at 19:57

1 Answer 1


Possibly a generic version of the SMBJ51A, a 51V SMB unidirectional TVS.

  • \$\begingroup\$ As mentioned in the comment of my original question. Can it be a TVS when it conducts at about 800mV (2A) when applying a postive voltage to the anode. And it blocks up to 60V when reverse biased? \$\endgroup\$ Nov 22, 2019 at 19:58
  • 1
    \$\begingroup\$ It is better to edit changes into your question at the bottom rather than to use comments. Yes, it's possible. If you read the datasheet I linked, the forward voltage is 800mV at 2A for a single die unit (the indicated construction), and it may not conduct more than 1mA at 62.7V. You would need more voltage than 60V to confirm. \$\endgroup\$ Nov 22, 2019 at 21:26
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    \$\begingroup\$ Thanks for reminding me; I will add it to the original post. I will try with a little more voltage and a proper multimeter. \$\endgroup\$ Nov 22, 2019 at 21:35

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