QuarterArcade Coin-Op Tech Net
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Pinout for WG NTSC Decoder
[Editor: This was originally posted on the newsgroup rec.games.video.arcade.collecting. It is saved here for reference.]
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 DC. The newer revision
PCBs (P600) have a Vcc of +12V DC, 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 over voltage protection
circuit (components not installed) as the Vcc was intended to be
supplied from a regulated power supply.
[Editor: these pins are not tied together. If you are building this
on your bench, make sure that both pins get +12V]
** This pin will have negative Sync output on it after the modification
*** 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.
[Ed: for a test bench, you don't need to connect blanking.]
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 chassis, the NTSC decoder needs to be modified.
After completing the modifications use +12V DC 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
1 x 3.3K resistor
50mm of wire
50mm 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.
Pinouts 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
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
Step 3. Cover the middle leg of the transistor and resistor with heat shrink
tubing to about 5mm (1/4") covering the other lead of the resistor.
Heat the heat shrink 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 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 the collector
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 heat shrink tubing so that
it will not short with any of the adjacent connections.
Step 11. 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.
Note: Only the newer NTSC decoders will have the capacitor installed.
Step 12. Solder one end of a 3.3K resistor to pin 1 of P203 and the other
end to ground. Ground is connected to Pin 3 of P203.
After completing the above 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 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.
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 procedure.
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.
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