Hi Rod.

--- "rod.badcock" <rod.badcock@...> wrote:

> Sorry I haven't posted back on this forum sooner!
>
> To answer some questions: the 'amplitude' I was
> referring to was the
> pulser trimpot - as the coil audible oscillations
> got louder I had
> assumed amplitude.

The trim pot is supposed to be set at build time and
left alone. When you turn it you can operate the
pulser WAY outside of it's specs. It is a wonder it
didn't blow out sooner.

>
> With regards the fitted 2N3904 I was mystified that
> after having
> worked for years I'm only now getting a problem
> (even when replaced
> with 2N3904) and caused me to question if that was
> all that was
> going on.

The one who's base goes directly to the pic through a
resistor?

That transistor gets hammered. If you crank up the
pulser, you will excede it's max ave current and cook
it.

I suggest you replace it with something more rugged,
and then set the pot to where it was when you bought
the pulser. Richard Lines can help you with that.

The next generation does not even have a pot. It is
set by fixed resistors.

I hope that helps.

Rick.

>
> .. If exceeding Vce is all that is happening then
> I'll swap them out
> for an 80V Vce ONSemi pin and function equivalent.
>
> Regards
>
> Rod
>
> --- In randrdesulfatorforum@yahoogroups.com,
> "linesrg48"
> <courtiestown@...> wrote:
> >
> > Rod,
> >
> > Yours was an early example and I cvan't honestly
> be sure of the
> > specification of the 2N3904/ 3906 devices
> originally fitted.
> >
> > I do now use the 60V rated ones available from
> Digikey.
> >
> > Rick has suggested trying a 2N2222/ 2907
> combination?
> >
> > Regards
> >
> > Richard
> >
> > --- In randrdesulfatorforum@yahoogroups.com,
> "rod.badcock"
> > <rod.badcock@> wrote:
> > >
> > > Hi,
> > >
> > > I have one of the Courtiestown PIC pulsers that
> has worked
> flawlessly
> > > for a couple of years.
> > >
> > > .... until now that is!
> > >
> > > I'm having problems with the FET drive section
> of the board,
> with Q2
> > > and Q3 (NPN 2N3904) blowing, causing the FET to
> remain in
> continuous
> > > conduction and blowing the fuse.
> > >
> > > Any suggestions from here on what might be going
> on? (seems to
> be
> > > related to amplitude)
> > >
> > > Rod
> > >
> >
>
>
>




________________________________________________________________________________\
____
Be a better friend, newshound, and
know-it-all with Yahoo! Mobile. Try it now.
http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ