re:G-05 pinouts

In message "G-05 pinouts", you write:

>I was just comparing the 12 pin connector pinouts on the Omega Race
>schematics with the G-05 drawing on Jess' web page, and they don't
>appear to match:
>
>G-05 Omega Race
>1 X in 1 Z in
>2 X gnd 2 Y in
>3 Y in 3 X gnd
>4 Y gnd 4 Z gnd
>5 Z in 5 Y gnd
>6 Z gnd 6 X in
>7 30 AC 7 30 AC
>8 GND 8 30 CT
>9 GND 9 6.3 AC
>10 30 AC 10 30 AC
>11 6.3 AC 11 GND
>12 HTR GND 12 HTR 0V
>
>checking the actual pinouts might be a good idea before plugging
>it in. the AC inputs appear to be equivalent, and I don't know
>if i'd trust my set of Omega Race schematics (I found drawing
>errors in the vector generator section)

The drawings, if they say what you indicate, are incorrect; HOWEVER it
may merely be a numbering convention problem (Midway decided to number
the pins in a different way than the Atari/Wells-Gardner/Electrohome
standard). Omega Race might, however, have another quirk; read on...
Below is the beginnings of my mono vector monitor fixit file...

First, let's make sure it is the PCB that is the problem and not the
monitor (which is much more prone to failures). Disconnect the 12-pin
Molex connector at the monitor. It has a pinout like this (use pin 11
to get oriented; pins 1, 3, and 11 are shaped like a "D" instead of an
"O"):

+----------+
| 1 2 3 |
| 4 5 6 |
| 7 8 9 |
| 10 11 12 |
+----------+

Flip the test switch inside the coin door and hit the reset button on
the game PCB (or power cycle the machine). This will put you into test
mode which will draw a very stable, all white screen (white is ideal
since the RGB values should be identical to eachother).

Set your meter for AC Volts and put the black lead into pin 8 of the
game harness (this is a ground and should be black). You should get
readings similar to the following:

Pin # Description AC Voltage
  1 X Out 6.68
  2 X Ground 6.68
  3 Y Out 6.69
  4 Y Ground 6.69
  5 Z Out 6.70
  6 Z Ground 6.70
  7 30VAC Center Tap 30.3
  8 Ground Center Tap 0
  9 Ground Center Tap 0
 10 30VAC Center Tap 30.3
 11 6.3VAC Center Tap 9.7
 12 Heater Ground 3.0

Bad game boards will usually have X, Y, or Z Out = 0 VAC. If you get
6-7 VAC on all of them then your game board is probably OK.

SPECIAL NOTE: (Some/All?) Omega Race games for some strange reason do
not use pin 12. Mine had a separate wire soldered directly to the
monitor board bypassing the connector and bridging the heater voltage
from another point.

Russel Willoughby <russel@iglou.com> discovered another potential
pitfall with Omega Race. Game board connector J7 to the monitor can be
put on BACKWARDS! The manual says that all of the connectors are keyed,
making it impossible to put them on backwards without forcing them; this
is obviously not true in the case of J7. The good news is that doing
so, even if the game has been turned on and left on for long periods of
time, does not cause any problems and everything should work if it is
put on properly (if it worked before).

If it looks like the game board is working then check all the fuses.
The monitor heater voltage for most of these games comes right off a
winding on the isolation transformer and through a fuse. This fuse is
VERY prone to becoming loose so make sure it is a good tight connection.

The next thing to check is the connectors on the monitor boards. They
are VERY prone to bad solder joints. In fact, I have NEVER seen a
deflection board which did not have this problem. Resolder them all
just to be safe.

The next most common problem with these monitors is the sockets on the
two transistors mounted to the chassis of the high-voltage power supply.
They like to become intermittent, especially the one on the regulator
transistor. Clean them and make sure they are making good contact.

About half of the monitors I work on have bad HV diodes in that the
leads and/or their connectors are corroded beyond belief. Many times
the diode will disintegrate to your touch. Please be aware that this
diode CANNOT be checked with a diode test function on a DMM nor with an
ohmeter; it is too beefy for those puny currents. If you don't have an
HV probe, the only way to test it is to put it into a known working HV
unit.

Rick Schieve <Richard.L.Schieve@lucent.com had some good advice about
replacing these. Cut off the bad connectors. Solder the new diode
directly to the bare wires (this is harder than it sounds, actually).
Coat exposed leads with RTV silicone (available at any auto parts store;
I use the red stuff). You must coat the exposed leads to insulate them
or you will get very dagerous arcing of HV all over the place.

David Hanes <davidhan@csn.org> posted the following information about HV
problems. It's from an article about the QuadraScan monitor.

Problem: 90v is less than 80v.

Procedure:
1) Measure the voltage on the anode of the Zener ZD900 or the emitter
   of Q901. The voltage should read 9 volts. If less, replace diode.

2) A key voltage measurement now must be made. Locate resistor R901
   near the top edge of the board between Q900 and Q901. This 1.2K ohm
   resistor stands up about a half inch off the board. Place positive
   lead on the lead of the resistor closest to the edge of the board.

   Voltage Probable Causes
   ------- ---------------
     9v Q901 shorted
    < 15v ZD901 shorted, Q900 or Q902 low gain.
     25v Open Q900, Q902, Q903, R906 or T900.

3) If all components are ok, the oscillator circuit (Q903) may be
    loaded down by a defective component in the seconday of T900.
    With an ohmeter, check the following components for leakage:
    D903, C909, C906, and C907.

    The other components D901, D902 and the doubler cannot be checked
    with an ohmeter. The following procedure may be used:

    Note: When working with the doubler, always make certain that the
           CRT anode is discharged to ground.

    Unsolder the wire going from the high voltage transformer to the
    terminal of the doubler. Apply power and measure the 90V (pin
    5 of R900). If the 90v comes up, replace the doubler. To
    determine if D901 or D902 are loading down the oscillator, unsolder
    one end of the diode and note if the 90v comes up to 90v.

Richardson Electronics in LaFox, Illinois (708.208.2200) has replacement
tubes for and they were extremely helpful. A 15" Monochrome XY costs
about $75.00.

Page 3 of the November 1979 Star*Tech Journal has a decent article
called, "Atari's X-Y Monitor Adjustments" which does an OK job of
describing how to properly adjust the deflection board.

     "Atari's new Quadrascan (tm) display system introduced in LUNAR LANDER
(tm) should be adjusted correctly at the factory for maximum resolution.
However, if brightness and contrast adjustments are required, plase
follow these procedures.

     Adjustments are made on the deflection
amplifier PCB located on the right side of the monitor when looking into
the rear of the game.

  1. Turn brightness (R516) and contrast (R526) all the way down
      (counter-clockwise).
  2. Turn up brightness until [the majority of] images are barely
      visible. NOTE: The stars [in LUNAR LANDER] may not be visible.
  3. Turn up contrast for desired clarity.

     This procedure will produce a very clear, bright picture, while
minimizing any chances of phosphor burn caused by over-adjustment of the
brightness control.

     NOTE: Only the brighness control (R516) and contrast control
(R526) on this PCB are "field adjustable". All other controls,
including X and Y linearity have been factory adjusted and should NOT be
tampered with.

--
THANX...Gregg   day 214.684.7380  night UNLIST/PUBL   TEXAS NOT CANADA!
              woodcock@nortel.com  or  woodcock@dfwmm.net
*CLASSIC VIDEOGAME COLLECTOR BUY/SELL/TRADE NON-COMPUTER (ARCADE/HOME)*
"If you quote me on this I'll have to deny it; I won't remember because
I have such a bad memory.  Not only that, but my memory is *terrible*."