Help with equivalent transistors for two QB2105CY

@fastmatt I am trying to repair an old speak and spell (the pcb shows it being the first version made when released #1033303-3G). After cleaning the battery contacts, I noticed one of the four transistors in the lower left of the power board (# BP 4023) was smoking. I’m wondering if your above comment on here on equivalent transistors is applicable to my board. Of the four, there are three different part numbers on the transistors (one CS9012D, one CS9013D, and two QB2105CY which is the type that burned out). Any suggestions on equivalents is appreciated.

Update (12/17/23)

@oldturkey03 Thanks for the response! In looking at the alltransistors website, it looks like I would use 2N3904 for the CS9013D, so I have two of the three, but like you I can’t find anything on the QB2105CY. Hopefully these three pictures come through.

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@sledhead70 use something like to find equivalent transistors. i.e. your CS9012D can be replaced with 2N3906 and multiple others. It's easy to use for as long as if finds your transistor. I checked on QB2105CY without success. Consider posting a good picture of this. Just post it on here as an answer. We can always clean this up after :-)


Can someone tell me if when I am searching for a transistor, do I need to use the leading and trailing letters? For example, the transistor I am trying to find is QB2105CY, but can I just search for 2105 or even B2105?

Barring that, is there a way to measure a transistor to determine the specs so I can find an equivalent? I know the tests to check for PNP or NPN but nothing beyond that.



I am likely on the wrong forum for help on identifying the above transistor, but I believe this QB2105CY is a JFET transistor, which if correct I just need to figure out if it is p-channel or n-channel.

What I did: I desoldered the second one thinking I could test it in a device I got on Amazon, which says it is just two diodes, and not a BJT NPN/PNP transistor. However, when I use my multimeter following some online tests for JFET transistors I don’t get the same readings, making me wonder if both are bad or I am barking up the wrong tree. I will follow up as I learn more, but if anyone has guidance I am open to ideas.