Testing H7864 (MicroVAX II) PSU With No Load

[Robert Jarratt]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
> Sent: 01 November 2015 18:54
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: Testing H7864 (MicroVAX II) PSU With No Load
> 
> 
> > That said, it's possible that there may be an auxiliary linear
> > regulator in there.  That's common  for additional outputs with modest
> > current needs, especially in older designs where the switching
> > circuitry takes a lot of individual components.  A TO-3 can isn't what
> > I would expect  to see in a switching-only supply.  In other words, that
> particular transistor might be the pass  transistor of a linear regulator.
> 
> There are plenty of suitable chopper tramsistors in TO3 packages. The
BU208 is
> the first one I think of (being this side of the Pond).
> 

This one is a D905.

> I've just looked up the printset for the 11/730 PSU (mine will be on the
bench
> soon I hope...). There are, as I said, 4 SMPSUs in there, 2 of them use
choppers
> in TO220 packages, the other 2 use choppers in TO3 packages.
>