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T/R switch, Q1, 2N7002

PostPosted: Mon Apr 13, 2015 4:57 am
by kz1x
For some odd reason, on one of my PBv2 radios, this part failed shorted, gate-to-source.

I need to replace it. By just looking, it seems like about any 2N7002 in this package will do.
They are about 20 cents in unit quantities, plus $5 shipping!

So, I wanted to check first to see if a particular version of this part was recommended.
David?

Re: T/R switch, Q1, 2N7002

PostPosted: Thu Apr 16, 2015 4:15 pm
by AE9RB
kz1x wrote:For some odd reason

I'm guessing you have an outdoor antenna and left the Peaberry connected to it last time there was lightning. Or it somehow sunk some ESD from another source.

kz1x wrote:So, I wanted to check first to see if a particular version of this part was recommended.

What do you mean?

Re: T/R switch, Q1, 2N7002

PostPosted: Thu Apr 16, 2015 5:33 pm
by kz1x
Well, there are probably a dozen slightly-different varieties listed on the Mouser and Digi-Key sites. Does one choose by cost? Brand?

How this one popped isn't all that important to me and I can't guess how it happened since the radio in question was sitting on a shelf for 2 months. I write off such events as anomalies.

I'll just put a new one in, when I learn if the part is just generic (as I suspect) or if the one you provided had some particular characteristic which you used to select it. For example, perhaps it has a lower-than-others Rds, or maybe a bit more source current rating, etc. There's no hint as to the OEM of the part marked 'LWW' you provide.

You should know that the Cypress chip soldiered on through the short, trying to service the RX line with 5V despite the strap to ground. No apparent damage.

Re: T/R switch, Q1, 2N7002

PostPosted: Mon Apr 20, 2015 7:43 pm
by kz1x
For anyone reading this thread, I was able to buy 50 pieces of this generic transistor, for about $3 -shipped- on eBay.
I installed one, and the radio worked again right away.

Now I have 49 spares.