I'm trying to work out the input portion of the input circuit on a digital RPM gauge. It accepts a W input from a standard automotive alternator.
I can't identify the JCL446 which only uses two of its pins, the 2TC or the E4ED diodes. What are the SOT23 ICs likely to be?
Best Answer
The JCL446 is most likely a diode (or dual diode) of some flavor or another
While I cannot find an exact match for the JCL446 in the SMT codebooks I checked -- JC seems to map to a BAW56 dual diode or a BAL74/BAR74 diode, and this would be consistent with only two pins of the component being used, as well. I would verify this theory with the second JCL part extending off the bottom right of your photo, though. (It's also consistent with the part having a reference designator of "D3" on the board's silkscreen.)
The 2T is pretty definitely a MMBT4403 PNP transistor
According to multiple datasheets, the 2T top mark is used for the MMBT4403 PNP small-signal transistor -- if it checks out as a PNP, then it's pretty definitely a MMBT4403.
And the E4's are pretty definitely MMZD5234 zeners
Again, according to multiple datasheets, the E4 top mark is used for the MMZD5234 6.2V zener diode. (If it's a Diodes Inc part, for which the full top marking scheme is an exact match, then the "ED" is a date code for December 2017.)