Tech: Modifying a Cosmic Chasm boardset to work with a G08-003

As per the request of several V-List members here is the
instructions for reworking a Cinematronics Cosmic Chasm board-
set to work with a standard G08 monitor. While the procedure
will correct the color intensity problems it does nothing to
help the crappy slew rate of the G08, your on your own there.

This modification is used to adjust the color signal (R,G & B)
levels of a Cosmic Chasm board so that they are compatible with
a standard Electrohome G08-003. When a CC boardset is run using
a G-08 there will be visible 'black level' or 'return-to-origin'
lines on the screen. The origin points will also be visible and
will burn several small holes in the phosphor relatively quickly.
The problem occurs because the CC RGB outputs are designed to
be compatible with a WG 19K6401 or Electrohome G08-005/CCO which
are 1V (BLACK level) to 3.6V-4.0V (full ON). The color levels of
the more common 19K6101 are similar. Why Electrohome chose 0-4V
is anyone's guess.
 To correct this the gain and offset of the RGB signals must be
modified. The mod is fairly simple and reversible in case you ever
get your hands on the correct monitor. It requires 6 resistors,
three potentiometers and some soldering skill.

Components required:
  QTY 3 15.4K 1% metal film resistor
  QTY 3 90.1K 1% metal film resistor
  QTY 3 25K potentiometer, Bourns P/N 3266W-1-253
                (Digi-Key P/N 3266W-253-ND)

Modification Instructions:

1) Carefully remove the three 9.1K resistors R1, R9 and R17 from
the Game Processor PCB. I suggest the following method: cut
one leg of the resistor right at the body and bend both the
resistor and the cut lead vertical. Heat the solder fillet on
the trace side and pull the resistor/lead out the component side.
Use a solder sucker to remove the left-over solder.

2) Install the 15.4K resistors in the R1, R9 and R17 locations.

3) Using a non-permenant adhesive (rubber cement or similar)
attach a 25K potentiometer to the top of IC U29, U14 and U15.
Orient the pots so that the pot's #1 lead is right above and close
as possible to the IC's pin #7 (+15V) and the adjustment screw is
on the side with pins 1 thru 4. Let the glue set.

4) For each pot bend the #1 lead down and solder to the IC's pin #7.

5) Using a short piece of wire-wrap wire connect the each pot's #3
lead to the IC's #4 pin (-15V).

6) Connect a 90.1K resistor between pin #2 of the IC and #2 lead
of the pot for each.

Power up the boardset. Connect a scope to the RED color output on
connector P2 pin 6. Note: all ODD numbered pins are GND. Adjust the
pot attached to U29 so that the signal level swings between 0 volts
and 4 volts. Repeat the adjustment for GREEN (U14) and BLUE (U15).

* Modification complete *

CAVEAT! - I have done this modification to two boardsets so far and
got the expected results. However, since electronics is three parts
Black Magic, two parts blood sacrifice and one part skill, I cannot
take responsibility for what occurs to your board should you make
this modification. All I can say is 'It worked for me".

David Fish "We want...Information. INFORMATION
Melrose, MA USA You won't get it!
   dfish1.at.mediaone.net By hook or by crook we will"
   David.Fish.at.axcelis.com _The Prisoner_

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Received on Mon Mar 26 15:05:10 2001