a new BBS...

24 Sep 2008

...
   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

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a new BBS...