[Coco] the XRGB-2+ upscan converter

[RJRTTY at aol.com]

OK ladies and germs,

     I have received the XRGB-2 converter from Pacific Game Tech
LTD. based in Hong Kong and here is the story:

     When I first opened the box and looked at the owners manual
my heart sunk.  The thing was written in chinese or japanese or
whatever.  I figured I was in for a tough time for sure.  A closer
look however revealed a lot of simple but informative line
diagrams and isolated english words like "RGB" and
"Video" occuring at strategic places throughout the manuall.
     The first thing I did was try the simplest hookup, namely
composite video in.   One of the concerns I had was that this
device might use the same chip and technique of the infamous
Matco converter.  That thing was no better than a hookup to a
standard TV.  When I connected this box up and powered up
the coco, the quality of the output was equal to that of the CM-8!!!
I am not exaggerating.  I dont know how they did it, but they
got the same bandwidth through that composite video port as
the CM-8!!  I guess this device is good enough and the CM-8
is poor enough so that they endup similar in performance.
The only significant difference in performance i could find between the
two was when the color-burst signal is turned off for
monochrome operation.  This is the code I used:

10 poke &hE033,16 :poke &hE03C,19 :poke &hE045,19
20 width 32 :palette 12,63 :palette 13,0 :cls
30 width 80 :palette 0,0 :palette 8,63 :cls1

This code turns the color burst signal off and sets up an 80-column
screen with white text on a black backround.  The XRGB converter
would either flicker at a rate of about 3 or 4 times a second
or would stablize and wash out with artifact colors.  It's like
it could not decide were to "settle" when generating the display. If you
execute a sound command the display would flicker and the
text would be ultra sharp for the duration of the command then
return to the stable but washed out color artifacted display when the
command finished.  I tried to attenuate the video output of the coco
thinking that maybe it was overdriving  the converter, but the result was
that it would stay in the flickering condition all the time.
     But if you delete line 10 in the above code and just set the white
forground and black backround, the converter display had the
same performance of the CM-8.   There was only the slightest
artifacting from the converter, almost imperceptable.  You can
adjust the converters programmable features  to minimize this. With
any color combination, this converter's composite video performance
is outstanding to put it mildly.  I guess the conversion process of this
device depends on ,in some way, the color burst signal for stability.

    All this is good but it does not justify the cost of the XRGB converter.
Now it was time to move on to the RGB input.  The manuall called it the
"game-in" input.   The manual included the pinouts labeled in
english (thank god ! ).  The connector plugged into the box and
was terminated with 5 RCA audio style female connectors.  Two
were actually for left and right stereo audio.  The other three were
for the three video signals and logically colored according to the signal,
Red, Green, and Blue.  This is were things get strange.  Remember, 
I'm feeling my way around in the dark with the language barrier.   I
noticed there wasn't any input for the horizontal or vertical synch
signals.  It occured to me that maybe they would be combined
on the green input or something like that.  (I had to go back to
school about the varies video standards to make sure I wasn't
missing something).  So I hooked up the signal lines with an opened
ended cable I keep for the coco for experiments like this and tried
various configurations with no luck.  I could see the display was
correct but there was no signal synch occurring.  Just the rolling
display.  I took another look at the diagram and it showed the synch
input on a certain pin on the connector but there was no connection
to it for that pin!  So I decided to disassemble the connector.  This
turned out to be easy.  A plastic nut that screwed onto the connector
held it together.  Once removed, it came apart into two pieces revealing
the solder lugs inside the connector.  I don't know if it was some kind
of design error or what but the pin that, according to the diaghram,
was supposed to carry the synch signals wasn't hooked up to
anything!!  
     To make a long story short, I soldered a wire to that pin and
brought it out from the connector.  After some scope time and
a few educated guesses, I determined that the synch signals
from the coco needed to be hooked up to a nor gate (74LS02) and
the output of that connected to the newly installed wire.  Upon
powering up the converter and the coco,  I saw what I had been
hoping for,  an SVGA image of the coco screen.  It looked every
bit as good as the screen of an emulator on a modern machine.
All color combinations and modes where sharp and clear (including
the color burst off - monochrome mode described above).  I may
get in contact with the manufactures to see what the deal is
with the missing input.  It could be that that input is rarely used over
there and they are unaware of the flaw.

     So this device works extremely well with the coco.  The only
problems are the cable hack and the high price.  You should
know that this is an extremely well built and feature packed
converter.  You can program almost every  aspect of its
operation.  You can adjust its scanning behavior to match
it to almost any monitor.  You can control the gain of the
red, blue and green signals independently of each other. Heck,
there are even adjustments for stuff I know nothing about. (what
the heck is "gamma" anyway?).  This converter can sync to
either 31khz or 47khz.  Could the latter one be for large LCD screens?
It has the composite video, RGB, S-video and another input I
don't recognize right off hand.  It even routes audio to your
PC's speackers.  And It all can be controlled with a remote with
the size and dimensions of a credit card.

     If any one decides to get this converter,  I can provide details on
the cable hack.   It was hard to find but easy to do.  I'll do the mod
for free if not to many people want it, just send me the cable.

     This device is not the ideal solution for the coco.  We need a
box that simply connects to the coco without all the unnessacary
bells and whistles at about 1/3 the price.   But this devices does do
exactly what I think everybody is looking for.


Vital statistics:      Manufacturer ----   Pacific Game Technology Ltd.
                                                       93 Kwai Fuk Road
                                                       Broadway Centre, Unit 
B, 17/F
                                                       Kwai Chung, NT
                                                       Hong Kong

                             Price + shipping - 209.00

                              email ---------------- www.lik-sang.com

Peace,

Roy R Justus
rjrtty at aol.com