Spot Killer Killer

  USB Relay   USB Extension Cable   Files

     When using a DVG with a WG6100 monitor, some games may appear to be missing all or part of the vectors being displayed on the screen.  This happens most frequently with Cinematronics games, but is also seen with Sega games like Star Trek.  If you take a look at your monitor chassis when this is occurring, you will see the Spot Killer LED lighting up.  The purpose of the spot killer is to turn off the video amplifiers when deflection is not occurring and prevent picture tube burn in.  Unfortunately, the 6100 spot killer is a bit too sensitive and negatively impacts games that only generate a small amount of screen activity.

    I chose to modify the 6100 Spot Killer circuit by putting a USB controlled relay inline with the Spot Killer LED(D800).  This allows me to selectively turn on or off the spot killer depending on the game being played.  

WARNING, if you attempt this modification, you are modifying a protection circuit on the monitor.  You assume all risk and should double check your work each step of the way.

Hardware

1.  Carefully remove deflection board from monitor.  Locate Spot Killer LED on the lower right hand corner of the board.  It is marked D800.  Carefully de-solder and remove LED being careful not to damage LED or its legs.

2. Bend one leg of the LED up and out.  Attach a jumper wire to the leg you bent.  Solder and heat shrink recommended.

3.  In the location on the PCB for the leg you just bent up, solder in a jumper wire.

4.  Carefully reinsert the LED with the one leg pointing down and solder back into PCB.  You should have one leg soldered in, one leg with a jumper wire, and one wire jumper from the PCB.  Try to avoid the ceramic resistor right in front of the LED when routing your jumper wires out.

5.  CHECK YOUR WORK.  Reinstall deflection board.  Temporarily attach the two jumper wires together.  Power back on looking for anything wrong.  Your spot killer LED should be lit and then go off when something is displayed on the monitor.  Power everything back off.

6.  Break the connection between the jumper wires.  Insert one jumper into the C(Common) terminal and the other jumper into the NC(Normally Closed) terminal.  By default we want the wires connected and Spot Killer On.  Power back on and everything should be the same as before.  Spot Killer will be active unless you send a command to the relay to open and deactivate.

I used a USB Extension Cable to put the Relay right next to the deflection board and keep jumper wires short.

    Software

    VMMENU calls vmm.sh when launching games.  This version of vmm.sh has been modified to call spotoff.sh to send command to usb relay to open when selecting games that need it and  spoton.sh before returning to VMMENU.  Script files should be placed in /usr/local/share/advance/. 

Technical Information

    Technical description from Atari TM-183 manual - "When either of the deflection amplifiers is not driving current through the deflection coils then either transistor Q801 or Q801 becomes biased so that it conducts, which turns on transistor Q800 and the LED D800 in its collector circuit.  When transistor Q800 is conducting, then transistor Q503 in the Neck PCB is cut off, forcing the red, green and blue amplifiers to turn off their electron beams."

    It should be possible to disable the spot killer by interrupting other components in the spot killer circuit, but the LED is very accessible and easy to modify.