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The Single-Chip Color Correction/Modchip Solution
(An Illustrated Example)
Abstract:
This example illustrates how the single-chip color-correction plus
modchip circuit can be implemented. The example is performed using an
SCPH-100x console model which has a PU-8 revision mainboard. The covered
topics are: module overview, module mounting, mainboard preparation,
wiring to the mainboard and assembly suggestions. Note that this is not
intended to be an installation manual, but rather a walkthrough of how
this type of modification might be done. Note: Some 1001-series NTSC
machines refuse to run PAL games. Most likely caused by the same software
incompatibility that causes many Japanese models to crash when trying to
run imports. Short of changing the kernel ROM, not much can be done
about this.
Disclaimer
Once again I must stress that this is not a project for beginners. It
is too easy to irreparably damage your machine if you do not know exactly
what you're doing. The author of these pages cannot and will not assume
responsibility for any damages that may occur while attempting this
project. You're on your own, folks.
Module Overview
The single-chip color-correction/modchip solution (which I call
Colormod) is a small circuit based around the already-popular
PIC12C508 microcontroller used by many mod chip vendors (most of whom use
my MODV53 source code). At left is an image of the prototype as installed
on the upper chassis plate of an SCPH-1001 console. The board measures
approximately 25mm by 40mm and implements the circuit shown below to the
right.
As can be seen, the circuit is quite simple. It is a textbook
implementation of a crystal oscillator as supported by the PIC12C508's
internal clock circuit. The key to its dual-purpose operation is in the
selection of the quartz crystal that determines the PIC's clock frequency.
For PAL color, this crystal has a value of 4.433619MHz. For NTSC color,
the value is 3.579545MHz. (The crystal on this module is hidden under the
board--it is too tall to mount on top. A low-profile version of the
crystal will fit on top, however).
As with a "standard" mod chip, the two signal lines (data and
gate) are present, as are the power supply leads. The only
curious component is the 2k2 resistor that connects to the "output" side
of the on-chip oscillator. The other side of this resistor is what
provides the colorburst clock needed for color correction, along with two
small modifications to the mainboard. Two 22 picofarad capacitors provide
stability trimming for the oscillator; the 0.1 microfarad and 10
microfarad capacitors provide power-supply decoupling--an important thing
to include in any digital circuit. The PIC is socketed for easy upgrading,
if needed in the future. The module is cabled to the mainboard by a
removable 10-pin dual-inline IDC ribbon cable connector, of which five
pins are used.
Module Mounting
I chose to mount the module to a convenient location on the upper
chassis plate for two reasons: I wanted to mount it in a solid, secure
location (as opposed to sealing it up in tape and wedging it under the
chassis plate as is done with many mod chips), and I wanted to make it
easy to change out PIC chips. (Remove the top cover and there it is--no
further disassembly or soldering/desoldering).
The module is mounted using a single 10mm (3/8 inch) spacer, screw and
locknut. The hole on the chassis plate is already there for the
SCPH-100x; I will post notes on mounting to a 55xx chassis plate as
soon as I get another one to work on.
In this view, the pins of the cable header are visible just below the blue
capacitor. The cable itself loops neatly under the space to the right of
the module. The top cover fits over the module without any problems.
Mainboard preparation
CAUTION: This is where things can get broken. If you are not
experienced in hacking on circuit boards, please get expert help.
To enlarge the image at right, click on it.
The first mainboard modification is to isolate pin 7 on the CXA1645 chip
then to connect it to one of two points. NOTE: In this example,
the color correction modifications are for a PAL console. Be sure
to make the modification according to the image. The "S"-shaped trace
indicated by the red CUT arrow should carefully have about 1mm-2mm
of the copper removed with a sharp X-acto knife. Pin 7, indicated by the
large blue arrow, should be connected to the point labeled GND1 for
a PAL machine. Use a small piece of thin, insulated wire such as the
"wire-wrap" wire sold at Radio Shack stores or other electronic shops.
For an NTSC machine, pin 7 should be wired to the point labeled
VCC1.
Pin 6 on the CXA1645 (the frequency input) must also be isolated. This
is done by carefully removing the surface-mount resistor indicated
by the orange arrow in the image at left. (Click on image to enlarge).
The best way to do this is to use a surface-mount soldering workstation,
but it can also be done using two low (17W max) wattage soldering
irons: apply heat to both ends of the SMD resistor and nudge it free.
Don't spend more the a few seconds heating the resistor or you might begin
to pull up the solder pads. This procedure is the same for both PAL
and NTSC machines.
The right-hand solder pad will be used as a wire connection point for
one of the Colormod module's cable leads.
(The resistor indicated by the red arrow does not need to be changed).
(Thanks to Walter Meyer for these two images).
Wiring to the Mainboard
(Detail top view of wire routing--click to enlarge)
The Colormod module is wired to the mainboard using a modified
10-conductor ribbon cable. The detail view of the insulation-displacement
connector at right shows how the 10 wires are crimped to the connector,
then every other wire is cut off about 1cm from the connector housing. Be
sure to align the marked end of the ribbon cable (look for the
small red dots on the wire furthest to the right as an example) with
pin 1 of the connector. If this is not done properly, you might
accidentally clip the wrong wires!
I used about 40cm of ribbon cable initally, then trimmed each wire to
appropriate length as I routed them to their locations on the mainboard.
The IDC connector has two rows of 5 socket holes, as can bee seen. Five
of these are not used; their wires have been cut away. The remaining five
wires connect to the lower row of connector holes. (I know the connector
is shown at an angle; use your imagination. ^^)
Wiring to the Mainboard, Part II
(Detail bottom view of wire connections--click to enlarge)
This chromosome-like detail image at left shows four of the five
wire-soldering locations on the mainboard. The fifth wire you may have
noticed already, it is soldered to the copper ground spring on the top
side of the mainboard. (Look for the big letter A in a circle; the
copper spring is just to the left of it). PU-7 and PU-8 mainboards have
these nice little holes to run wires through, incidentally. Use them
^^.
The topmost wire is the "data" wire for the mod chip function. The wire
just below it is the "gate" wire for the mod chip function. If you have
worked with mod chips before, these locations should be familiar. See the
mod chip
wiring instructions (under the SCPH-100x section) for more info.
The wire in the lower right corner is the +5 Volt power supply wire. It
is also described in detail in the mod chip wiring instructions.
The remaining wire is what sets this whole project apart from a regular
mod chip. This is the colorburst frequency signal that connects
from the 2k2 resistor on the Colormod board to the right-hand solder pad
where that SMD resistor was removed. (see detail image, above).
Assembly Suggestions
The wires on my ribbon cable look like this:
Wire number Signal Name
----------- -----------
1 (marked) +5 Volts
3 Ground
5 Mod "Data"
7 Mod "Gate"
9 Colorburst
This corresponds to the header pin order on my Colormod board. Remember
that since every other wire is clipped off, only the odd-numbered wires
carry signals. Wires 2, 4, 6, 8 and 10 aren't there.
PAL users: you want a 4.433619MHz crystal.
NTSC users: you want a 3.579545MHz crystal.
Oh, and you might want this: The PIC12C508 source for
this project.
In the Future
I have made a commercial version of the Colormod board. It includes a
few additional options: a jumper location to allow selection of NTSC/PAL
timing mode for the PIC and a two-pin connector location to allow the
attachment of a "mod-function disable" switch, which won't affect
color-correction.
One final note: this board can also be used for a stock mod chip. It
can work with a 4-wire chip by leaving all but the decoupling capacitors
off, or work with a 5-wire chip by installing a jumper wire after removing
unneeded components. See the Mod Chip Module
overview.
I will post an announcement on the REI web site when I have boards
available for interested folks.
Dedicated to all the Aussies who emailed me asking about color
correction...
Access count:
Scott Rider -- chip@aeug.org
