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Super 8 wrong transistor?
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Author:  Kenwitb [ Mon Feb 01, 2021 10:31 pm ]
Post subject:  Super 8 wrong transistor?

Bank 6 led lights up on power up. All buttons act normal and all banks selectable except 6. Suspected short because could hear relay on application of power, so double checked an no visual shorts. Removed PIC controller, bank 6 lights up and can hear relay on power up. Decided to look at transistor to see if there was a short there and noticed the font looked different than other transistors. Closer exam it appears to be a 2N5458 (jfet?) rather than a 2N5088 npn. I’m sorry I missed it when sorting out parts in the start of build.


Edit: Solved... Removed 2n5458 and relay was no longer activating with power on, placed a 2N3904 I had to correct the issue. Seemed to work fine so soldered in place and now all relays test fine. Leaving all of this here for the next guy.

Let me know if you think mixing 2n5088 and 2n3904 will be a problem.

Author:  duhvoodooman [ Tue Feb 02, 2021 10:14 am ]
Post subject:  Re: Super 8 wrong transistor?

Yep, you nailed it. Scroll down through this sub-forum and you'll see the same problem reported (and solved) a few times. BYOC received a shipment from a supplier that had some 5458 JFETs mixed in with the BJTs they had ordered, and didn't realize it for awhile. And JFETs obviously do not function correctly in this relay switching application. But as you found out, a 3904 (and pretty much any other general purpose NPN BJT) will do the job here.

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