Re: Amplifone MC1....

I updated the Amplifone FAQ ver1.1 into adobe .pdf format. The HTML conversions
just didn't work very well.
   

MKDUD@aol.com wrote:
>
> In a message dated 2/8/00 10:31:59 PM Eastern Standard Time, jess@magenta.com
> writes:
>
> << Hi all,
> I decided to smash up one of my Magnetic Correction Units to see what was
> inside since I didn't think it has been documented here. It came apart quite
> nice after sitting in the freezer all day. What I found was sort of puzzling
> (to
> me at least) can anyone help explain this....
> >>
>
> WoW!! I was allways to parinoid to take one apart, for fear I was
> destroying a part that is difficult to replace. Ed, are you listening? Did
> you ever disect the one we pulled of that damn blue board a couple years
> back??
> I'm going to repeat Zonn's explanation of the MCI - this appears in
> version 1.1 of my Amplifone HV faq, but is NOT on the HTML version 1.0 on
> Jess' GameArchive site. (You can get version 1.1 from GameArchive, but it's
> in DOC format):
>
> http://www.gamearchive.com/video/manufacturer/atari/vector/monitors/amplifone/
> amphvfq11.doc
>
> ____________________________________________________________________
> It seems fairly apparent that the HV section of the Amplifone is regulated
> much
> like that of the old (and maybe some new) constant voltage AC supplies that
> use
> ferro-resonant transformers.
> Basically the idea is that a transformer can only be driven to a maximum
> voltage, after which it saturates and an increase in input voltage does not
> correspond (nearly as much) to an increase in output voltage. This maximum
> voltage, before saturation, is highly dependent upon the resonance frequency
> of
> the transformer.
> The constant voltage AC regulators use a capacitor to tune a winding of
> an
> isolation transformer to 60hz, causing the transforming to go into saturation.
> After which voltages of around 70v to 140v input has little effect on the
> output, and changes in current loading also have a much smaller effect.
> Pretty
> cool.
> If you look at the schematic of the Amplifone HV you will see no
> feedback from
> the output voltage, back into any sort of regulator. In fact the Amplifone
> contains no HV regulation circuit of any kind! (With the exception of the
> over
> voltage regulator, see the following note.)
> The 555 is simply set to a frequency, which drives (unregulated) the Q1/Q2
> amplifiers, which drive the primary of the current boost transformer T1, which
> drives Q3, also with no regulation!
> I have no way of knowing exactly what's inside MC1, but the only way for
> this
> circuit to regulate it's output voltage, given changing output currents, would
> be for some type of ferro-resonant regulation to be taking place. MC1 must
> be a
> type of tuning coil, possibly a coil and capacitor, that along with the
> inductance of T2 is used to set the resonant frequency of a ferro-resonant
> regulator. (Which is probably why T2 is so expensive and hard for other
> companies re-engineer.)
> These companies are probably winding the HV to give the
> proper increase in voltage, but not taking into account it's inductance and Q
> ratings, which in most HVTs are not nearly as critical. As a result, when it
> comes time to test the transformer in the circuit, they fail at regulating the
> output voltage. Just a guess mind you, I wonder if anyone could verify this?)
> MC1 combined with T2 must form a resonant circuit. As the 555 is brought
> closer/farther from the resonant frequency of MC1/T2 the voltage coming out is
> higher/lower.
> ___________________________________________________________________
>
> Thanks again, Zonn!
>
> Just another side note, (this is also in the faq, but I've been getting
> ALOT of questions from people about this). If your Amplifone HV unit is
> blowing +/- 24 regs like crazy, and killing precious BU406D's, and you are
> getting an INCONSISTANT waveform at the base of the BU406D, start suspecting
> that the MCI may be bad.
> The damn thing is often located very close to the 5w 50 ohm resistor
> near the reg, and the high heat from the resistor can sometimes damage the
> MCI. If the red MCI case looks a bit deformed from the heat, suspect a bad
> "red mystery can" if you are getting the above symptoms. Try to keep the 50
> ohm resistors away from the regs and MCI.
> Sorry for the ramble, but I thought it was neat that Jess decided to
> disasemble the MCI. Maybe now we can figure out a way to test MCI's???
>
> MK
>
>
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Received on Wed Feb 9 02:24:13 2000