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I have a shorted sot23 with only the letter A written on top.
After hours of searching online, I haven't found anything with only the marking "A" on top.
How do I identify this component and find one to replace it with?
An unknown SOT23 package component with effectively no part number could contain just about anything unless you know the context in which it is being used. Without a part number to go on, your best bet is to try and determine its function in the circuit and try to work out what kind of component it might be. From there, it *might* be possible to find an equivalent part.
It might be a simple transistor, or it could be a custom IC, or even a small voltage regulator. If it is just a transistor, you may be able to determine what kind of transistor it is (BJT, MOSFET, JFET), and find a transistor to replace it with that would meet the necessary system specs.
At work, with all the bills of materials, known suppliers, parts specifications, I decided to place a direct phone call to just find the markings on those tiny SOT to a manufacturer we bought from.
Their explanation was . They put any marking they want, changed the next day or week or whenever for the same exact device. Like to identify their production batches, not to relate what it is. As the components are reeled, the reel has all the identification, period. Not at all consumer oriented, but OEM oriented.
So forget about reliably identifying markings on SOT23.
By the way... could your SOT23 on schematic be a double diode ?
The only thing to make it through those two diodes at X3 would be high a frequency drive depending on direction. As for the SOT markings could represent anything really, all tho just for a slim chance possibility (this is guess working the part!) The A marked SOT-323 under Motorola NPN RF 8GHz, MRF947.
Just using SMD codebook Marsport. Usually has some results show accurate for older to somewhat recent small IC components such as SOT.
Also again this would not change the circumstances if a manufacturer has changed the part lettering to what they wanted for self reference as mentioned and the new lettering could lead to a wrong part that has the same lettering by developer of another completely different part even with same casings when checking for those parts.