Laser Tuning (Sega Saturn)
The Sega Saturn has several versions, but most versions have various potentiometers you can use to tune the laser.
Before you start tuning any of them take a photo of their exact position from the side.
There is also a basic power adjust potentiometer on the actual laser head.
The basic potentiometer on the laser head is the main one everyone tunes. However it is one of the least critical.
Start with looking at where it already is. Usually the 202 text on the 2k potentiometer is facing up (about 1k), at 2 O'Clock (700R) or at most it should be at 4 O'Clock (500R).
Personally I find anything past 3 O'Clock is too powerful and won't work. A good setting for the power is as shown in the image above, about 45 degrees which will give a resistance of around 750R).
Start with that, and move the pot clockwise or anti-clockwise in tiny movements until you get good disc spin.
Ignore the game reading or not, just focus for now on if the disc spins and continues to spin for a while.
By far the most important tuning step is getting the lasers focus distance just right. This is the distance from the bottom of the disc to the laser head.
The laser (left of image above) moves up and down to a specific position in order to focus the laser on the underside of the disk held in by the disc holder (center of image).
The optimal position is 1.6mm from the holders base to the shrouds top.
It is easy to accidentally push down the disc holder when removing discs over time.
The holder sits on the steel rod of the motor under friction only, so if you push down firm enough it will move down.
Using a vernier measure the distance from the holder to the plastic shroud and set it to 1.6mm. If you do not have a vernier the position is usually just before you can see any gap between the holder and shroud.
Certain laser board versions have the F. OF potentiometer. This stands for Focus Offset and you can turn it to further fine tune the laser head distance from the disc.
This is the most critical thing to get right for good disc reads. First set the physical height to 1.6mm and then you cannot be far off, and fine tune by turning the potentiometer left and right through trial and error.
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Another crucial setting, but one that is usually set perfectly is the EF Tracking potentiometer.
This adjusts the center point of the data that sits on the DC offset. When data is read from a disc the data waveform should have a DC offset (usually around 2.5V) and the data should swing equally high and low above it (usually 0.35V above, 0.35V below, 0.7Vpp).
Tuning the EF potentiometer is required if you have an oscilloscope and can accurately observe the actual output from the laser during disc reads and you see the wave being off-center from the DC offset.
If you do not have an oscilloscope do not adjust this. It is a very accurate tune and rarely needed.
The remaining two potentiometers are for gain (boosting the output from the laser). Tune these last.
Focus gain boosts the focus for the pits and hills in the disc (so focusing on the discs depth), and the tracking gain boosts the gain of the disc moving in and out of the disc (the wobble/difference in distance from the inner area of the disc to the outer area as the distance changes.
