Alt-BEAM Archive

Message #05228



To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Sat, 10 Jul 1999 10:41:27 -0400
Subject: [alt-beam] Re: Something funny with the 1382 voltage triggers?




Steven Bolt wrote:

> On Fri, 9 Jul 1999, Bob Shannon wrote:
>
> > > Btw, if you are sure they are the same, why bother comparing them
> > > with a curve tracer? Am I missing something?
> >
> > Yes, your missing the fact that I physically swapped parts
> > between a working thru-hole photovore that used the same
> > electrical configuration.
> >
> > So with the same physical solar cell, motors and capacitors, the
> > thru-hole SE's work while the SMT ones lock up.
>
> Ok, perhaps there is a language barrier here. You swapped the
> parts; that means you took the thru-hole parts from the working SE
> and put them into the SMT SE, which still didn't work?
> And the SMT transistors did fine in the thru-hole SE?

Or a reading barrier.

I swapped the physical solar cell, physical capacitor bank, and same
physical motors.
I did not substiture with similar parts, I swapped the very same parts.

I also tested many sets of SMT active components, all act the same (full
sun lockup).

I also tested many sets of thru-hole parts, all acted differently than the
SMT parts, with
no lockup problem detected.

> In that case, you have proved that the SMT transistors are not the
> culprits. No need to bother with that curve tracer.

You have misunderstood me here. The lockups have only been seen when using
any and
all sets of SMT parts. Lockup has not been seen, nor deliberatley
introduced into the
thru-hole SE's by lowering the resistor values to levels well below the
measured values
in the SMT SE's.



> > Its just that simple.
>
> Your suspecting the SMT devices put me on the wrong foot, it seems.

Please take no offence here, but I dont beleive your in the right foot yet.

> This phrase in particular:
>
> > I heard today that SOT23 transistors are not made from the same
> > dies used for the TO92 packages, due to bonding wire attachement
> > issues. It seems that they are not quite the same parts.

Exactly so, if this is true.

You see, with the only (known) variable being the packaging of the voltage
trigger and transistors, the lockup problem reliably follows the SMT parts,
not
the solar cell, not the caps, and not the motors (resistor values being
measured as
equal).

Why is this so hard to express here? The same parts dont have a problem
with
thru-hole parts, but lock up with SMT parts.

> Anyway, I still wonder what you expected from that curve tracer, if
> you were diagnosing by swap.

Well, I'm suspecting that the Vbe of the SMT NPN part might be different,
or the gain of
the PNP, or something along these lines.

I am not 'expecting' anything, I am investigating ~if~ any electrical
difference actually
exists.



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