Re: Major Havoc -> Tempest Adapter Schematic

At 01:24 PM 8/29/97 -0700, you wrote:
>
>Could someone scan in the schematic for the adapter board
>to put a Major Havoc into a Tempest? I've noticed there are
>subtle tweeks to the multiplier values for the different
>game implementations, and was wondering if this circuit was
>identical to that on a Tempest.
>
>Also, does anyone have any opinions why the Quantum PCB
>HAS the XY correction circuit, when it shipped with an
>Ampliphone monitor?
>
>I was wondering, Zonn, which games you have tried your
>modified WG monitor that drives the deflection amps from
>the unregulated supply? On games with the correction
>circuit, is the display "overcorrected" now?

Weve done a bit of experimenting with driving the deflection circuits with
unregulated voltages, and regulation just the HV. It doesn't change the
pincussion correction at all, but it does have an affect on the vector
stability. You just can't get the solid non jittery display that you can
get with a regulated deflection supply.

I believe the problems goes back to that current feedback design. In an
audio amplifier (which I was using as my justification for removing the
regulator) the feed back is the voltage across the speaker. If the supply
voltages change, the feedback will still keep the voltage across the speaker
rock solid because of the feedback in the error correction.

The deflection circuits get their feedback from the other side of the yoke,
and it appears it needs a constant voltage in order to properly control the
varying current. I'm unsure of all the math behind the what happens when
you vary the voltage on an inductor, and then control the current through
it, and what exactly happens. But based on experimentation all I can say is
that if you regulate the deflection circuits, you can acheive a very stable
rock solid display. If you don't, your display is going to jitter.

The jitter is not real bad -- in an arcade I'm sure most wouldn't even
notice. It does make me wonder how a properly working Amplifone compares
with a regulated WG for vector steadiness.

But for now I owe Gaymond a GO-8 fix. Yuck.

And on that note, the Cosmic Chasm I have uses a GO-8-CC0, which is the
beefed up version of the GO-8-CB0 which is every Sega Monitor I've seen
except for the Cosmic Chasm.

One thing cool about it is that it uses the higher res Amplifone type 19" tube.

They've re-laid out the circuit board to remove all the daughter boards and
use heftier heat sinks (no more of thos copper foil things). And according
to a paragraph in Gregg's X/Y FAQ, these were supposed to have other changes
that fixed all there old problems. Right. Of course I've never had any
problems with this monitor, and it was *working* when I got the game!

The biggest change is the output drive transistors. They're using STD-1064s
which I couldn't find an exact spec on, but I did find a cross to a
"similar" Motorola part, the 2N6465. It has a slightly lower current rating
(8 amps instead of 10) but the voltage surges on the new transistor is huge.
over 450v, or over 800 volts if the base is floating, and has been
specifically designed to withstand a certain amount of reverse breakdown
voltage *without* being destroyed.

The data spec claims its specifically designed to run deflection circuits
and other inductive loads. They're the only ones in the Motorola manual
with these ratings, that had the needed gain to replace the current ones.
If I had to pick a replacement, these would have been them.

This certainly helps justify Rodger Boots claim that the killer of these
deflection transistors is not current/overwattage but inductive kicks.
Rodger works on military monitors that are capable of switching back and
forth between raster and vector mode on a frame by frame basis. (Allows for
built in overlays on a vector display --- Coooooool!). He says the big
killer is voltage spikes and thought some properly chosen 500v MosFets might
be made to work -- with some redesign. It looks like Sega found some
transistors with the same ratings.

This make some sense to me since I've never had a deflection transistor
"Melt down" -- unless the CPU has died and left the transistor at maximum
deflection. They mostly seem to die at the off/on transition -- or for now
particular reason. I've had Tempest just "go out" on me, and I immediatly
felt transistors. They were not at any "melt down", boil a drop of water (I
wet my finger first!!), temperatures -- but the heatsinks could quickly
dissapate this heat, so who knows.

I found 6 of these transistor (2N6465) at a surplus store and bought them.
Gaymond's G-08 needs some new deflection transistors, I'll try these and let
you know how they work.

-Zonn
Received on Fri Aug 29 14:13:09 1997