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Pin-outs for the Wells Gardner NTSC Decoder

This decoder is made on a small square PCB and has the model number
DY-1-0 at the end of the PCB with the corner cut off. There are two
basic revisions, 85X0172 (P371) and 85X0311 (P600). 


P204: 1 - Vcc *
      2 - Vcc *
      3 - GND
      4 - Key
      5 - Blanking Input

P203: 1 - Positive composite Sync out
      2 - Key **
      3 - GND
      4 - Video Blue out
      5 - Video Green out
      6 - Video Red out


 *   The Vcc is dependant on the revision of the PCB. The earlier revision
     PCBs (P371) have a Vcc of +15V. The newer revision PCBs (P600) have a 
     Vcc of +12V, although, +12V still works with the earlier (P371)
     revision PCBs.
     The difference between the two versions is with R256. It is used to 
     lower the voltage from +15V to +12V, on the earlier revision PCBs.
     The newer PCBs, using regulated power supplies as Vcc source, just 
     have a wire link in the place of the resistor.

     The newer revision also did not have the overvoltage protection circuit
     enabled (components not installed) as the Vcc was intended to be
     supplied from a regulated power supply.

 **  This pin was used to supply +12V and blanking in some (modified) versions.
     They were altered to suit some games, so take note when using an old
     revision decoder.

How can I use this NTSC decoder in my JAMMA cabinet?

To enable this decoder to be used with a JAMMA cabinet, without modifying
the harness or monitor, the NTSC decoder needs to be modified.

After completing the modifications use +12V as the Vcc supply for 
the NTSC decoder.

The following parts will be required for the modification:

  1 x 2N3904 transistor
  1 x 3.9K resistor
  1 x 4.7K resistor
  60mm of wire
  40mm of 3.2mm heat shrink tubing 


Note: All references are to the solder side of the PCB unless otherwise noted.
      Read the entire step before proceeding with it.

      Pin-outs of the 2N3904 transistor: while looking at the transistor with the
      ID lettering right side up (legs facing downwards) the left leg is the 
      Emitter, the middle leg is the Base, and the right leg is the Collector.

      Take care when locating components on the PCB, as the part IDs are close
      to adjacent parts and it would be easy to incorrectly identify a part.

Step 1.  Cut the middle leg of the 2N3094 transistor leaving approximately
         5mm (1/4"). Do the same with one end of the 4.7K resistor.

Step 2.  Solder the short end of the 4.7K resistor to the Base (middle leg) of the
         2N3904 transistor. It is easy to do if you first tin both the transistor
         and resistor ends with solder, then put both ends together and heat.

Step 3.  Cover the middle leg of the transistor and resistor with heatshrink
         tubing to about 5mm (1/4") covering the other lead of the resistor.
         Heat the heatshrink tube.

Step 4.  Locate R256. There will either be a resistor or a wire link installed.
         If there is a resistor installed, remove it and install a wire link.

Step 5.  Locate Q204 (2N3906). Near Q204 is a black wire (on the parts side)
         which is soldered onto the PCB, between R224 and R223. On the solder
         side of the PCB you will notice that there is a track going from the
         solder pad, where the black wire is soldered, to R224. Cut the track
         between the black wire's solder pad and R224.

Step 6.  Position the 2N3904 transistor under the BNC connector (on the solder
         side of the PCB) so that the flat side of the case is facing the the PCB
         and the leads are pointing towards P204. Solder the Emitter (lead closest
         to the edge of the PCB) of the 2N3904 transistor to the end of R224 
         closest to the edge of the PCB (GND). 

Step 7.  Solder the end of the resistor, which is connected to the base of the
         2N3904 transistor, to the end of R224 closest to Q204. 

Step 8.  Solder a wire from the end of R224 closest to Q204 (or to emitter of
         Q204, as they are connected by a short track) to the blank solder pad
         on the track located between pin 5 of P204 and R222.

Step 9.  Solder the Collector of the 2N3904 transistor (remaining leg) to the 
         solder pad where the black wire (on the parts side) is soldered to the

Step 10. Solder one end of the 3.9K resistor to the collector of the 2N3904
         transistor (same location as in Step 9) and the other end of the 3.9K
         resistor to the closest end of R256 (wire link). Before soldering the 
         resistor, cover enough of the resistor with heatshrink tubing so that
         it will not short with any of the adjacent connections. 

After completing the above mentioned steps, recheck the modifications to ensure
that they have been done properly. Make sure that the track mentioned in step 5 is
cut properly.

The NTSC decoder is now ready to be used in a JAMMA cabinet. 

If your monitor has trouble with the sync from the NTSC decoder, and the 
modifications have been done properly, then remove the capacitor from the black wire
that goes to the end of the PCB near P203. Install the black wire directly to the
PCB. Only the newer NTSC decoders have the capacitor installed, to remove any DC
offset from the sync.

If the picture's colour is not stable or completely absent then the APC control
will have to be adjusted. The luminance bias adjustment may also need adjusting,
if the APC was not incorrectly adjusted in the first place.

PCB adjustments:

    The Tint, Color, Contrast, and Sharpness adjustments are straight forward to
    make when using a color adjustment pattern. All laser disc games have the
    pattern in their self test options.

    Do not adjust the APC or Lum(inance) Bias adjustments. If you suspect that
    one or both require adjustment then follow the following proceedure.

APC Adjustment:

    1. Apply a color bar signal to the Video Input terminal.
    2. Turn the Color control fully clockwise and position the
       Tint control at its mechanical center.
    3. Connect a jumper between TP201 and ground.
    4. Turn the APC adjustment control until the color bars on
       the screen are synchronized.
    5. Remove the jumper from TP201 and ground.

Luminance Bias Adjustment:

    1. Connect a oscilloscope to one of the three video outputs.
    2. Turn the Lum. Bias adjustment fully counter-clockwise.
    3. Slowly turn the Lum Bias adjustment in the clockwise direction until the
       black level is just at the sync tips. The sync appears fully compressed.

Ruben Panossian


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