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Modding your MV1FZ for stereo sound is a pretty simple process, so it shouldn't
take a lot of time to perform.
The first thing you need to do is locate where to tap the stereo
signal on the 1FZ. The following image is from the bottom side of the 1FZ
board. Look around the board and locate this area as this is where you will tap
the signals. I have marked three places of importance which I will explain
below.
The stereo signal comes into the 1K resistors marked R37
(A) and R36 (B), along the right side of the image. The stereo signal is
summed (into mono) with a third signal (C) that comes directly from the
YM2610 audio. I haven't looked real close as to why it is a seperate line but
without it, you will be missing some sounds. This line is played over both the
left and right channels. For your reference, (A) = Right Channel, (B) = Left
Channel, and (C) = YM2610 Analog Channel.
To get stereo out of the 1FZ, the first thing that you will need
to do is break the audio merge. You can do this by removing R36 and R37. By
doing this though, you have lost the YM2610 analog channel that gets mixed into
the mono signal. What you will need to do is wire up a small circuit to add the
YM2610 analog channel into each stereo channel.
Now that you have the two resistors removed (R36 and R37), you
will need to solder three pieces of wires to the pickup points indicated in the
first image, as shown in the next image. I would recommend wire about 6 inches
long to give you enough working area.
Now that you have the wires attached to the 1FZ board, you will
need to build a small circuit that will mix the YM2610 Analog Channel (C) with
the Right Channel (A) and Left Channel (B). The circuit is very simple and only
requires four capacitors (4.7u) and four resistors (6.8k). The schematic
and board are shown in the following image:
In the above photo, the Right Channel (A) is the top wiring coming
in from the left. The middle wire is the YM2610 Analog Channel (C), and the
bottom wire is the Left Channel (B).
In my testing, I just wired the Left and Right leads up to the
RCA jacks on a consolized 1FZ and used the MVS Test Menu to verify that stereo
was working. I didn't spend a great deal of time on this so if your audio is
backwards, I may have mislabeled the LEFT and RIGHT channels :) I didn't wire
the Left and Right channels to the MVS JAMMA edge to see if it was ample sound
for a cabinet as my only goal for this was on a consolized system. In any case,
it's a pretty simple mod and could be expanded on to fit your needs.
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