31 May
2010
31 May
'10
5:07 p.m.
On 29/05/2010 19:33, Chris Elmquist wrote:
I have brought my SWTPC 6800 system back to life that
I built as a kid
in 1976. It is pretty heavily loaded with RAM cards, floppy controller,
etc. and the 8V power supply rail was never really able to hold its own.
It sits at about 6.5V now... driving many 5V regulators on the various
cards. No where near enough margin going into those.
I had the same problem with the power supply in my SWTPC floppy drive unit.
2) add a new transformer to the existing supply just
for the 8V rail.
This will also fit but requires moving the existing transformer, cap,
DC distribution board-- all efforts that require drilling new holes in
the chassis. This would be a more authentic solution since I wouldn't be
introducing power supply designs that didn't exist back then. There were
actually published mods along these lines in the day but I am little
hesitant to butcher the chassis to accomplish this.
What I did was replace the silicon rectifier diodes with Schottky
diodes, which have a much lower voltage drop. Problem solved. Assuming
your existing transformer can actually produce enough current from the
secondary, that might be enough for you too.
--
Pete Peter Turnbull
Network Manager
University of York