I don't know what kind of multimeter you have, but all meters do not have the
red lead positive when in the Ohms position. When checking fwd and rev
resistance of semiconductor junctions it becomes a factor.
73, Jim wd4air
> Date: Sun, 13 Mar 2011 10:02:59 -0700
> From: ural.jim@gmail.com
> To: tentec@contesting.com
> Subject: Re: [TenTec] 255 Power Supply
>
> Is there a way to check the SCR? I pulled the board this morning and upon
> closer inspection it is discolored at the base where the leads emerge.
>
> I ordered a couple of the transistors from Mouser and will add the SCR to
> the order.
>
> Jim
> K6JEA
> On Sun, Mar 13, 2011 at 9:08 AM, Dr. Gerald N. Johnson
> <geraldj@weather.net>wrote:
>
> > The transistors are wired in parallel, but that 0 resistance from base
> > to one of the connections is a shorted junction in one of them. There's
> > no repair possible for the transistor, it must be replaced. When you
> > take them out, you can tell which is bad, but a sturdy pair isn't a bad
> > investment.
> >
> > .514 is about right for the forward drop of a silicon junction. OL is
> > right for open. Which a junction should be one way. .000 for both
> > polarities of the meter shows the shorted junction.
> >
> > 73, Jerry, K0CQ
> >
> > On 3/12/2011 10:23 PM, Jim Anderson wrote:
> > > After searching Google on how to test a transistor I realized I was doing
> > it
> > > wrong.
> > >
> > > Here are the new readings...
> > >
> > > On the Diode function and the black lead on the base it reads .514 on one
> > > terminal and .000 on the other
> > > With the red lead on the base it reads OL on one terminal and .000 on the
> > > other.
> > > Both transistors give the same results.
> > >
> > > On the 2K ohm scale with the red lead on the base it reads 1.2 on one
> > > terminal and .000 on the other
> > > With the black lead on the base it reads 1.1 on one terminal and .000 on
> > the
> > > other.
> > > Again, both transistors give the same results.
> > >
> > > Thanks for sticking with me on this.
> > >
> > > Jim
> > >
> > >
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