Re: New Monitor: Center tapped transformer

I think Jeff was thinking that people that were buying this monitor as an Atari
replacement already had one, therfore the need to get another was not needed for them
in particular.
  Sega owners would be at a loss unless finding a way to use the 90V CT transformer in
those cabinets were possible.

If you (James) need a Transformer for testing, let me know. I have a spare Tempest
Transformer that I will donate to the cause.

James Nelson wrote:
>
> Fine. What do they cost?
>
> ----- Original Message -----
> From: jeff hendrix <jhendrix@Quark.Com>
> To: <vectorlist@lists.cc.utexas.edu>
> Sent: Monday, November 08, 1999 11:24 AM
> Subject: RE: New Monitor: #2 CIRCUIT FOR REVIEW
>
> > All the atari color xy games have a 50VAC center tapped transformer
> already
> > built in.
> >
> > -jeff
> >
> > -----Original Message-----
> > From: James Nelson [mailto:nelsonjjjj@didactics.com]
> > Sent: Monday, November 08, 1999 8:34 AM
> > To: vectorlist@lists.cc.utexas.edu
> > Subject: Re: New Monitor: #2 CIRCUIT FOR REVIEW
> >
> >
> > OK, I found some cheap non inductive power resistors, and I can include
> the
> > fuses to save the yoke from fire.
> > I'll fix the mute resistor (thanks for catching that), and of course put
> big
> > caps at the device.
> >
> > Now, If you don't want a switcher, I'm all for not building the dang
> thing,
> > but can you (or anyone) help me find out where we can get a supply of
> > inexpensive new, high power 200W? 110VAC in to 48VAC out center tapped
> > transformers so I can derive the +/- 30VDC. By inexpensive, I mean like
> $20
> > ish, not $50. Alternatively, we could use two 24V 100W transformers (not
> as
> > pretty.)
> >
> > I'll get a new schematic out soon
> >
> > Thanks,
> > James
> >
> >
> >
> > ----- Original Message -----
> > From: Rodger Boots <rlboots@cedar-rapids.net>
> > To: <vectorlist@lists.cc.utexas.edu>
> > Sent: Monday, November 08, 1999 2:35 AM
> > Subject: Re: New Monitor: #2 CIRCUIT FOR REVIEW
> >
> >
> > > It is I, the mighty Circuit Shredder, returned for a rematch. So, let's
> > see
> > > where the nasty surprises are this time.
> > >
> > > First of all, I know you all want it, but stay away from switching power
> > > supplies for a vector monitor. Switchers work great with stable loads
> but
> > have
> > > one hell of a time when the loads keep changing (exactly what a vector
> > monitor
> > > does). With very careful design a high-frequency switcher could be made
> > to
> > > work, but design of one is not for the faint of heart.
> > >
> > > Ignore sense resistor inductance at your own peril. Or better yet, look
> > at a
> > > game where somebody has put in normal wirewound resistors in something
> > like a
> > > Tempest. See all the little jaggies in the lines? There is nothing
> that
> > says
> > > you can't use 10 10 ohm 1 watt non-wirewound resistors in parallel you
> > know.
> > > You even spread the heat out better that way as a bonus.
> > >
> > > I know the spec sheet says you don't need a fuse, but put one there
> > anyway. You
> > > don't need a shorted IC (it's not a matter of IF, it's a matter of WHEN)
> > burning
> > > up a yoke. Or at least getting the yoke wires hot enough to shatter the
> > CRT. I
> > > know it's far-fetched, but PLEASE keep the fuse.
> > >
> > > Mute pin (pin 8) can't be tied directly to the negative supply, there
> must
> > be
> > > resistance there. Say 22 k ohms or so. This pin is a current (not
> > voltage)
> > > driven pin. 22 K ohms will give you a touch over 1 mA. Current has to
> be
> > over
> > > .5 mA, but the graphs all stop at 10 mA (all bets are off when you leave
> > the
> > > graph).
> > >
> > > The power supply .1 uF capacitors will need at least some heavy
> > electrolytics
> > > across them (100 uF or more). All of these will need to be VERY close
> to
> > the
> > > amplifier pins.
> > >
> > > R1 and R7 need to be VERY close, preferably the same pad group. If the
> > power
> > > supply caps and IC ground connect to the same group it's better yet.
> > >
> > > For the real purists out there, the resistance on each of the input pins
> > of the
> > > amp should be close to the same. Practice is just too picky for words,
> > but has
> > > to do with thermal stability (amongst other things). And get the value
> of
> > R2
> > > down. This beast driving an inductive load is going to be hard enough
> to
> > > stabilize without unexpected phase shifts from high value resistors.
> > >
> > > That's enough of that, I guess. The parts you have marked as "none" are
> > going
> > > to be real interesting to pick. You might want to use the original
> > monitor
> > > board design as a guide for at least a starting point since these are
> very
> > > dependent on yoke inductance. OR find an engineer that know his poles
> > from his
> > > zeroes to calculate them for you. I never was any good at the pole/zero
> > stuff,
> > > but without it it will be hard to get things stable. I suppose you
> could
> > dump
> > > it all into a Spice simulation and see what flies. At least some good
> > starting
> > > numbers could be arrived at that way.
> > >
> > >
> > > James Nelson wrote:
> > >
> > > > Hi everybody!
> > > >
> > > > This deflection circuit design is very simple, and that's the beauty
> of
> > it
> > > > :-)
> > > >
> > > > The LM3886 has all kinds of protection built in to it, so many of our
> > past
> > > > concerns are finally addressed, such as overvoltage, undervoltage,
> > > > overloads, shorts, thermal runaway & instantaneous temperature peaks!
> > > >
> > > > I will probably need to design an on-board switching power supply and
> a
> > > > decent spot killer (I'm not sure if it justifies a microprocessor at
> > this
> > > > point) as well as connectors for hookup. There may be a special
> > oscillator
> > > > for Sync inputs on the conversion monitor. This would stabilize the
> > High
> > > > Voltage section.
> > > >
> > > >
> >
> http://www.angelfire.com/nh/northamericantelecom/images/deflectionamp02.gif
> > > >
> > > > Don't mind the wrong symbol for the yoke.
> > > > Fuses are not required due to the protection inherent to the 3886.
> > > > I believe the sense resistor inductance, in this design, is
> unimportant
> > due
> > > > to yoke inductance being orders of magnitude more significant. 1-10
> > uH -vs-
> > > > 1 mH.
> > > >
> > > > Please keep in mind, I'm trying to keep the parts cost to an absolute
> > > > minimum so the max people can afford it. It also means, hopefully,
> that
> > I
> > > > won't have to invest $5000 in a parts stock just to have 20 boards on
> > the
> > > > shelf.
> > > >
> > > > Design comments, complaints and criticisms, as usual, are requested.
> > > >
> > > > Thanks everyone!
> > > >
> > > > James
> > > >
> > > > http://www.angelfire.com/nh/northamericantelecom
> > > > low cost regular phone service click links to 6.9c or 5.9c no monthly
> > fees!
> > >
> > >
> >
> >
Received on Mon Nov 8 12:46:23 1999