a new BBS...

[Tony Duell]

> > It is not unherad-of for a colour monitor, at least not in the UK, to
> > have a flyback transofmrer producing 8kV or so and a separate
> > diode/capacitor votlage tripler module. The latter generally provides
> > the focus supply. Some Microvitec monitors (commonly used with the BBC
> > micro) and the Acorn Cambride Workstation's internal monitor (a
> > Microvitec chassis, of course) were like this.
> 
> I was of the impression that most of the current crop of stuff used those 
> multipliers.

Most colour monitors that I've worked on have what I think is known as a 
'diode split transformer'. The EHT rectifier diodes are sealed inside 
the flyback transformer, I believe the EHT winding is made in serveral 
sections with diodes between them (electrically), and the capacitance 
between the windings acts as part of the smoothing circuit. But it's not 
a voltage multiplier.

Some monitors, mostly 1980's ones, have a semarate voltage multiplier 
module (nearly always a tripler) connected to a flyback transformer 
giving about 8kV. Certaionly Microvitec used this. I think at least one 
of the IBM PC monitors (EGA?) did.
> > > > In many colour monitors, the dynamic (edge/corner) convergnece is set
> > > > by tilting the yoke, settign that up takes a long time.
> > >
> > > No,  that's static convergence and color purity.  Typical early TVs had
> > > an
> >
> > I disagree.
> >
> > On delta-gun CRTs (unlikely to be found in colour computer monitors, but
> > there are a few 1970's ones), the purity is set by ring magnets on the
> > back of the youke (they look like the cnetring magnets on a monochrome
> > CRT). 
> 
> Right.  That was a part of the process.  The other part of it was the 
> forward-rear adjustment of the yoke.  BTDT...   :-)

Yes, I think you're right. It's been a long time since I worked on a 
delta gun CRT (although I still have a couple in use here...). I do 
rememebr the wing nuts holding the feflection yoke to its housing, I 
rememebr slackening them, sliding the yoke to one end (far back?), 
adjusting the magnets to get a red patch in the middle (with a red-only 
video signal coming in, of course), then sliding the yoke forwards to get 
it to fill the screen.

> 
> > The xtatic convergence is normally set by 3 permanent magnets on 
> > the 'convergence yoke' -- a Y-shaped thing bechind the deflection yoke on
> > the CRT nexk with a separate 'blue lateral' unit behind that. 
> 
> Yup.  Sometimes the convergence yoke was a separate assembly,  sometimes it 
> was a combined assembly with the deflection yoke.

Over here it was nearly always a separate unit.

> Excepting one Trinitron TV that I brought with me when leaving NYC (in early 
> 1978,  and it's still working fine although a little dim),  most of what I 
> worked on was earlier stuff,  delta-gun arrangement.  The inline-gun stuff 
> didn't start to take off really until after I got out of the business.  I do 
> know that they sure took a whole lot less fiddling with than the earlier 
> stuff did.

The problem comes when the yoke shifts from the factory-set position. 
Setting it up is a _lot_ harder than a delta-gun CRT in my experience. 
Some manufacturers recoemend replacign the CRT/yoke assembly if this 
happens, but I am certainly not rich enough to do that...

-tony