Re: Amplifone Design... Wonders me

From: Zonn <mlists_at_zonn.com>
Date: Tue Mar 09 2004 - 14:18:22 EST

On Tue, 9 Mar 2004 18:59:21 +0100, "mypearl" <mypearl@dds.nl> wrote:

>Hello Group,
>
>I've been posting before about my Star Wars with amplifone that is giving me a wobbling image.
>
>After a lot of testing and replacing old components on the amplifone deflection board, I found that If I connect my regular lab power supply to the amplifone's + and - 30V rails, the wobbling goes away and the picture is rock-steady! I just connected the + and - 30 VDC to the AC power input on the Deflection board.
>
>This means the Amplifone (or mine) isn't very good in rejecting power supply ripple.
>
>The ripple on the supply rails is about 200 mV AC RMS, what doesn't seem to be extraordinary considering the currents involved.
>
>I understood from someone that the biasing transistors Q3 and Q13 are extremely of influence when it comes to power supply ripple, but that section seems fine and I've replaced both the 3904 and the MPSU57, as well as the 914 diodes (by 1N4148's) on both channels. I also installed 10.000 MFD capicators with low ESR specs for the main filter caps.
>
>I cannot believe the image on every Amplifone should be wobbling somewhat. Can anybody confirm that it should be very stable?
>
>What for Atari's sake could cause the deflection board to be so sensitive to power supply ripple?

No low voltage regulation.

I noticed this a long time ago. Every properly working Amplifone I've owned has
had a less stable picture than every properly working WG6100.

The Amplifone's whole reason for existence was price reduction (and maybe supply
problems with the WG6100 as well). The first thing they got rid of was the low
voltage power regulator -- they replaced it with a wire. The second thing they
got rid of was the high voltage regulator, it was replaced by a
feroresonance(sp?) design that does not regulate as well as an active regulator.

>From a manufactures point of view, this made the Amplifone a much nicer design.
Wires are much more reliable (and cheaper!) than the highly unreliable low
voltage regulator design in the WG6100. In the HV section the poor design of
the WG6100's HV section was also replaced by a wire (ok a coil, but it's just a
long wire wrap around something).

If it wasn't for a manufacturing defect in the Red HV transformer, these
monitors would most likely have been very reliable.

>From a collector's point of view the removal of active regulation in the two
critical parts of the monitor's design leads to shaky vectors and a screen that
blooms when more vectors are drawn (leading to even more shaky vectors).

In an arcade most of the players aren't going to pay much attention to a little
shakiness on the display, as long as the game is working, they'll play it.

But when it's in your collection it can bug the hell out of you!

The solutions are to regulate the LV and HV sections yourself. By using a lab
supply like you did, you restored regulation in the LV section. Another
possible solution is to back fit a LV2000 (you'll need to mount a couple of
heatsinked power transistors somewhere.)

For the HV section your most likely best bet now is to use one of the newly
designed HV replacements Fred's come up with. Before that it would mean
retrofitting a WG6100 HV section into a Amplifone, but the WG6100 HV section
itself, was not a great design from both an engineering and reliability
viewpoint. It'd be better to just get the Wintron HV xmfr.

The Wintron HV will restore the reliability of the Amplifone, but it still lacks
decent HV regulation.

-Zonn

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Received on Tue Mar 9 14:02:33 2004

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