Sega Saturn (Model 1) CD Drive Adjustment

A Japanese HST-3200 Saturn (Model 1) with the top case off: the power supply board on the left, the CD drive in the middle and the shielding over the main board on the right (photo: Evan-Amos, public domain)

On the Sega Saturn (Model 1) Sega's PAL service manual gives a check for a worn pickup and four servo adjustments on the CD drive's own circuit board: R114 (FE bias), R111 (focus gain), R104 (FE balance) and R113 (tracking gain). Sega follows the same sequence after fitting a new pickup. The manual covers drive unit 610-5679-20 or -21 in the PAL MK-80200-50. Other Model 1 consoles have drives from other makers: one PAL Model 1 restored in 2024 had a JVC EXL-P604 CD-ROM board. Before adjusting anything, check that your drive's board carries the trimmers and test points where Sega's Fig. 6-1 shows them.

The trimmer on the pickup's APC board is not one of these. Sega sets it at the factory and warns that turning it may damage the laser diode; low laser output means a worn diode, and the pickup is replaced.

Symptoms

Sega's description of a drive out of adjustment:

Faults from incorrect adjustment (Sega PAL service manual, p. 9)

Adjustment	Too low	Too high
Focus gain (R111)	The lens cannot focus and the disc does not turn	Parts of a track are skipped and noise increases
Tracking gain (R113)	The drive is more sensitive to knocks; parts of a track are skipped or the time counter stops	The lens may oscillate, giving unstable or distorted sound

A worn laser diode gives a low RF level. Sega's figure is 0.8 to 1.4 Vp-p for the eye pattern at the RF test point with a disc playing; below 0.8 Vp-p the pickup should be replaced. A dirty lens and faults elsewhere in the console can look the same: work through the Sega Saturn (Model 1) Troubleshooting Guide first.

Safety

• Laser: when the beam has to be checked, observe it from more than 30 cm from the objective lens. The console is a Class 1 laser product, but there is invisible laser radiation when it is open with the interlocks defeated.
• Mains: the Saturn's power supply is inside the case and runs from AC 220-240 V on the PAL machine. The adjustments are made with the console switched on and the top case off, so keep hands and probes away from the power supply board. See Capacitor Failure Symptoms and the Sega Saturn (Model 1) Maintenance Guide for the supply.

Tools and parts

• Sega's test equipment: an oscilloscope, a DC voltmeter, a non-metallic adjustment screwdriver and the A-BEC TCD-792A test disc.
• For the two scope connections in Sega's Figs. 6-2 and 6-3: two 10 kΩ resistors, a 10 µF electrolytic and a 0.01 µF capacitor.
• A marker, to mark the trimmers' positions before turning them.
• A replacement pickup, if the RF level is low. Read the part number on the old pickup before ordering. One owner fitted a new Optima-6 pickup to an NTSC-J Model 1.

Procedure

Sega's Figs. 5-1 and 5-3: the six screws (A) for the top case, five in the base and one at the back, and the CD drive unit with its two connectors and flat cable

Open the console

1. Unplug the mains lead.
2. Remove the six screws (A) and slide the top case off in the direction of the arrow in Sega's Fig. 5-1. The figure shows five in the base and one at the back. Adam Wilson's write-up of a PAL Model 1 and an iFixit guide both count five screws on the underside.
3. To take the drive out, disconnect its two connectors and its flat cable and lift it out as Sega's Fig. 5-3 shows. Adam Wilson found one screw under the drive holding its ground strap, and the iFixit guide describes the same; remove it as the drive is lifted.

Check the pickup

1. With a disc playing, measure the eye pattern at the RF test point (Fig. 6-1). 0.8 to 1.4 Vp-p is normal; below 0.8 Vp-p, replace the pickup.

Replace the pickup

Sega's sequence after a pickup change:

1. Switch off and unplug the mains lead.
2. Replace the pickup. Some replacement pickups arrive with a solder blob for static protection, which has to be removed before use: Walter Comunello's new pickup would not focus until he removed it.
3. Set the door-close detection switch to on by hand and switch on. The laser should emit light for about 3 seconds while the lens moves up and down. Do not bring your eyes close to the laser.
4. Check the FE bias, then adjust the focus gain, the FE balance and the tracking gain, as below.
5. Check that the eye pattern can be seen at the RF test point, 0.8 to 1.4 Vp-p.

Sega's Figs. 6-1 to 6-3: the trimmers R104 (FE), R111 (FG), R113 (TG), R118 (BPI) and R114 (F. OFF), the test points FE IN, GND, VC, TEST, RF and BPI, and the filter connections for the oscilloscope

Prepare

1. Mark the present positions of the variable resistors.
2. Build the two filters: for FE IN, a 10 kΩ resistor in series with the probe and 10 µF from the probe side to VC (Fig. 6-2); for BP IN, a 10 kΩ resistor and 0.01 µF the same way (Fig. 6-3). The oscilloscope's ground goes to VC in both.

FE bias (R114) and focus gain (R111)

1. Connect the oscilloscope to test point FE IN as in Fig. 6-2.
2. Switch on and set the CD drive to stop mode.
3. Adjust R114 (FE bias) so that the DC voltage at FE IN is 0 V.
4. Play the first track of the test disc and adjust R111 (focus gain) so that the DC voltage is −7 mV.

FE balance (R104) and tracking gain (R113)

Sega's Fig. 6-4: the waveform at BP IN, centred on VC, with 0.4 V amplitude after adjustment

1. Connect the oscilloscope to test point BP IN as in Fig. 6-3.
2. Switch on and play the first track of the test disc.
3. After play has begun, connect the TEST pin to GND.
4. Adjust R104 (FE balance) so that the waveform is centred on 0 V.
5. Adjust R113 (tracking gain) so that the waveform's amplitude is 0.4 V, as in Fig. 6-4.
6. The adjustments affect one another. Repeat them two or three times.

After fitting a new pickup to an NTSC-J Model 1, Walter Comunello found the disc would spin but the lens would not settle; he brought the FE setting slightly down with an oscilloscope, and the drive then read an audio CD.

Reassemble

Refit the drive with its connectors, flat cable and any ground-strap screw, and slide the top case back on with its six screws.

Testing

Checks after adjustment

Check	Where	Expected
Laser and focus search	Door-close switch on, at power-on	Laser lit for about 3 seconds; lens moves up and down
FE bias	FE IN, stop mode	0 V DC
Focus gain	FE IN, first track playing	−7 mV DC
Tracking gain	BP IN, TEST to GND	0.4 V amplitude, centred
Pickup	RF test point, disc playing	0.8 to 1.4 Vp-p

Then play games and audio discs from start to end. Skipping, a stopping time counter or distorted sound point back to the focus and tracking gains, as in Sega's table above.

Revision notes

Sega's manual documents one drive, 610-5679-20 or -21. Adam Wilson's PAL Model 1 had a JVC EXL-P604 CD-ROM board, so the drive in a given console may not be the one Sega documents, and its trimmer positions and designators may differ. The Sega Saturn (Model 2) has later main boards and drives; check its drive against Sega's figures in the same way before using this procedure.

Related pages

• Sega Saturn (Model 1)
• Sega Saturn (Model 1) Troubleshooting Guide
• Sega Saturn (Model 1) Maintenance Guide
• Sega Saturn (Model 1) Capacitor Replacement Guide
• Sega Service Manual - Sega Saturn Pal - 1 June 1995