Laser Tuning (PS1)
Depending on your model of PS1 there are several things you can calibrate when tuning the lasers.
The following are the potentiometer names (if labelled) and their purpose:
- RV701 = Focus Gain Error Correction
- RV702 / RV703 = Tracking Gain / Pull-Push Adjust
- RV704 = Focus Error Bias
The following test pads are visible on some models.
- CL704 = RF_O (Output Amplified RF Signal)
- CL706 = GND (Ground)
- CL708 = OEM (Focus Error Output)
- CL709 = TEO (Tracking Error Output)
- CL710 = VC (Voltage Center)
- CL711 = FEI (Focus Gain Error Input)
- CL751 = P.P (Tracking Push-Pull)
If you want to tune the laser by the eye pattern, you can probe the test point RF (CL704) on the main board and tune it based on th service manual.
Every single PS1 has the ability to tune the laser diode current through a potentiometer on the side of the laser.
Using a multimeter set to mV DC (if you have millivolt, if not use normal volt), probe the top pin of the potentiometer with the red probe, and the black to ground.
With no disc in, press down the lid close sensor to make the laser diode move up to the top position. You should see if physically move up. While it is at that top most position for a second you want to read the voltage on your multimeter.
The reading wants to be 11.4mV or slightly above.
You can fine tune this laser to suit your console, after tuning other aspects, but the base starting point is 11.4-11.9mV.
With the laser intensity set, the next thing to tune which has the largest impact on tuning is the DC BIAS potentiometer.
The DC BIAS adjusts the DC voltage offset by moving the laser head closer to or further away from the discs surface.
Increasing the BIAS increases the voltage, moving the laser closer to the disc. Reducing the voltage moves it further away.
The BIAS potentiometer simply connects to VCC (pin 2 of CN702) through the pot, and the voltage divider output goes to the CXA1782 FE_BIAS pin 37.
You can also adjust the bias via the eye pattern.
Some PS1 have the RV702 or RV703 potentiometer for adjusting this wobble. Later boards don't require adjustment and are automatic.
Proper adjustment requires an oscilloscope, a special test disc (SCD-2700) and a way of turning off the tracking servo.
For any optical drive (CD, DVD, BluRay etc) the laser automatically follows the grooves running around the disc by moving the lens back and forth slightly to stay in-line. This is called (tracking). This is because all track lines on optical discs are neither perfectly centered nor perfectly circular.
The PlayStation exploits this tracking by purposely having a wobble in the start of the first track called a wobbly groove.
The console now monitors the tracking movements the laser has to do to follow this groove and extracts a signal out of this. After this, a string can be extracted from that signal. This string is either SCEI (for Japan and Asia discs), SCEA (for North America discs) or SCEE (for all PAL region discs).
This string is then compared to an expected value, which differs depending on the region of the console. Hence, this method combines both, copy protection and region locking.
The focus tracking can also be adjusting using the eye pattern.
The Focus Gain / Focus Error Correction is set on some models (others it is automatic) via RV701.
This potentiometer adjusts the amplitude of the focus error correction, this is an alternating voltage (AC) added or subtracted from the default bias DC voltage in the event of fluctuation.
The gain is to track the up and down wobble in the disc, trying to maintain a smooth DC signal overall, with the AC data overlaid.
If the gain is too low, the coil that moves the laser head will not move enough to keep the laser and disc at the same distance from each other fast enough.
If too much gain the coil will hiss due to too much oscillation compensated by counter-oscillations at high speed (frequency). The discs will usually read very good but premature wear of the actuator is to be feared in the long term.
The right setting is the result of a trade-off between too much gain and less life span and and too little gain with failed reads.