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I’m repairing the main control board for a HVAC unit that was damaged in a power surge. Nothing too complex, just a diode that was blown and needs to be replaced.

The problem is I’m not exactly sure what part number the diode has and I want to make sure I get the right specs for the replacement (like how much voltage it can handle and whatnot.)

I’ve attached a picture of the diode, and you’ll see it has markings that may seem like a part number but Google did not yield any results. To further that the exact same board for another damaged HVAC unit has different markings for the same diodes.

These are for the compressor and exhaust fan signals for any curious souls (but are scattered all along the board.)

Anyway, could someone help me identify a proper replacement? The measurements for the diode, not the the mount, are approximately 4.2 mm x 3.5 mm. The top says “CT” by the way, and the bottom of the diode has no markings.

enter image description here

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2 Answers 2

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It appears to be a Littelfuse SMAJ43A ~50V unidirectional TVS diode, based on the document here. If you can add the dimensions of the part to your question it would help confirm.

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  • \$\begingroup\$ That looks like the one, and matched the marking tag “CT”, thank you! \$\endgroup\$
    – Chase Grochett
    Commented Aug 18, 2022 at 20:04
  • \$\begingroup\$ @ChaseGrochett Be sure to check the package dimensions, it might be an SMB as in Spehro's answer. It looks a little wider than an SMA, but hard to tell definitively from the photo. \$\endgroup\$
    – John D
    Commented Aug 18, 2022 at 20:16
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It's a TVS, made by Littelfuse. Probably an SMBJ43CA 43V bipolar type, but check the dimensions of the package.

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  • \$\begingroup\$ Looked like it might be an SMB to me too wasn't sure, but the SMAJ43A has the CT package marking as well, so package dimensions would help figure out which one it is. \$\endgroup\$
    – John D
    Commented Aug 18, 2022 at 20:15
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    \$\begingroup\$ @JohnD I think the aspect ratio is more like an SMB. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Aug 18, 2022 at 20:28

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