Document ID: TOS-OPT-REF-005 Revision: 1.0 Author: ThisOldScot
Section_1: Overview#
In the Borders Lab, the “Handshake” is the moment the console logic takes command of the physical drive. While the laser provides the RF signal (TOS-OPT-REF-001), the Digital Signal Processor (DSP) and Servo Controller manage the four critical loops that keep the laser on track.
If a console “Sees” a disc (laser fire) but fails to spin it up or keep it playing, the logic handshake has failed. This guide outlines the protocol for tracing the communication between the DSP and the Motor Driver IC.
Section_2: The Four Pillars of Servo Control#
| Signal Loop | Acronym | Function |
| Focus | FE / FO | Moving the lens vertically to maintain the focal point. |
| Tracking | TE / TR | Keeping the laser centered on the spiral data track. |
| Sled | SL | Moving the entire pickup assembly across the disc. |
| Spindle | FG / MDP | Controlling the RPM to maintain Constant Linear Velocity. |
Section_3: The Probing Protocol#
STAGE_3: 01 // The Focus Handshake (The “Breathe”)#
Before the disc spins, the laser must find focus.
- The Test: Use an oscilloscope to probe the FO_OUT pin on the Driver IC.
- Analysis: You should see a slow triangular wave as the lens “hunts” up and down. If the lens doesn’t move, the Driver IC or the Focus coil is open.
STAGE_3: 02 // The Spindle Kick-Start#
Once focus is achieved (indicated by a “Focus OK” signal), the DSP tells the Spindle to spin.
- The Test: Monitor the MDP (Motor Drive PWM) line.
- Analysis: You should see a flurry of high-frequency digital pulses. If the pulses appear but the motor doesn’t move, refer to TOS-OPT-REF-002 (Motor Torque).
STAGE_3: 03 // Tracking Error (The “Jitter” Check)#
If a game skips when the bass is loud or the console is bumped:
- The Test: Probe the TE (Tracking Error) line.
- Analysis: A healthy TE signal should be a centered AC waveform. If it is offset toward the 5V or Ground rail, the “Tracking Balance” is out of calibration.
Section_4: Forensic Logic Analysis: “No Disc” Diagnosis#
If the laser fires and focus is achieved, but the system still returns “No Disc”:
- Check the EFM (Eight-to-Fourteen Modulation) data line at the DSP.
- If EFM data is present (shimmering noise on the scope) but the DSP doesn’t acknowledge it, the DSP Crystal (XTAL) may be vibrating out of frequency.
- Replace the 16.9MHz or 33.8MHz crystal to restore the DSP’s “Sense of Time.”
Section_5: Technical Warning#
Safety_Warning
DRIVER IC THERMAL ALERT: Motor Driver ICs (like the BA6397 or BA5810) get extremely hot during the handshaking phase. If a motor is partially shorted, the Driver IC will enter “Thermal Shutdown.” If the chip is too hot to touch within 10 seconds of power-on, do not continue testing; you risk permanent substrate damage.
Section_6: Practical Application: Sega Saturn “Logic Hang”#
If a Saturn’s laser moves to the center and taps the disc but never spins:
- Probe the FOK (Focus OK) pin on the DSP.
- If FOK stays Low (0V), the DSP never “authorizes” the motor to spin because it doesn’t think it has a valid reflection.
- This points to a Mirror Surface Failure or a dead RF Amplifier IC, not a dead motor.