Sega Saturn (Model 1) Maintenance Guide

Sega's circuit board diagram for the 837-11493 VA0 PAL main board. CE45 and CE46 sit beside the position marked FUSE at the lower left.

Routine care for an early Sega Saturn — the machines in the first case design, built on the VA0, VA0.5 and VA1 boards. Much of it applies to later boards too, but designators and fitted parts vary by revision, so read the silkscreen before trusting a designator here.

Before you open it

The Saturn is mains-powered. The PAL machine is model MK-80200-50, rated AC 220–240 V at 50/60 Hz, drawing approximately 20 W, and it takes a detachable mains lead; Sega's accessories list gives three leads, for the UK, for SOE territories and for Australia. There is no DC adaptor and no barrel jack.

Inside, the supply is a bought-in switching module — Fujitsu, Panasonic, Phihong, Voltek or Yamaha depending on the machine and market — with a bulk capacitor on its primary side rated 200 V or 400 V.

That capacitor holds charge after the lead is pulled, and the mains tracks beside it are live whenever the console is plugged in. Unplug the lead, measure across the bulk capacitor and discharge it through a resistor before touching the supply. Done that way, servicing the supply is ordinary work, and on a machine this old it is very often the most useful thing you can do to it.

Strip-down

Sega's own order, with its screw counts.

1. Six screws, then lift the top case off.
2. CD compartment lid: two screws and the bracket lid spring; the spring itself; two screws and the oil damper; then push the lever to release the boss and lift the lid away.
3. CD drive unit: disconnect two connectors and one flat cable, then lift the drive out.
4. SH-1 board: four screws and the top shield plate, then one screw and three tabs.
5. Main board: four screws holding the CD drive unit supports, then five screws.
6. Power board three screws, power indicator board one screw, R.SW board two screws.

Cleaning

• Case. A damp microfibre cloth. Nothing abrasive — the finish marks easily. For yellowing, read Retrobrite first.
• Controller ports and cartridge slot. Isopropyl alcohol on a swab or a soft brush, dried fully before power is applied.
• Vents and board. Dry air or an anti-static brush.
• Lens. A cotton swab barely damp with isopropyl alcohol, wiped gently outwards. Let it dry before the lid closes.
• Sled rails. Remove the old hardened grease before applying anything new; mixing the two makes the sled worse. Use a plastic-safe grease, sparingly.

Rails to check

From Sega's block diagram, at the main board's power connector.

Rail	Feeds
+9 V	CD drive, and the PLL
+5 V	All chips other than the SDRAM
+3.3 V	SDRAM

There is no +12 V rail and no negative rail on a Saturn. A maintenance table that asks you to look for −12 V on a blue wire, or +9 V on an orange one, is describing a PC supply, not this machine. Sega does not publish colour-coded wire assignments or tolerance bands for the Saturn's rails, so none are given here — measure against the nominal figures above and treat a rail that is visibly low or noisy as the fault.

One more thing that catches people out: on the VA0 PAL board the position silkscreened FUSE is filled with a jumper wire (Sega part 600-6458, "JUMPER WIRE L=10MM"). There is nothing to test there, and continuity across it proves nothing about the supply. console5 records the same practice from the other direction — many VA0 to VA0.8 boards were assembled with a jumper in place of the fuse and zero-ohm resistors in place of the ferrite beads.

Capacitors

Early Saturn main boards use surface-mount aluminium electrolytics, and leakage from them is the most common age fault on this machine: distorted or missing audio, video noise, random resets, discs that will not read.

Every position by board revision is on Sega Saturn (Model 1) Capacitor Replacement Guide, which also carries the power supply and CD-ROM board lists. What each failure mode looks like is on Capacitor Failure Symptoms; cleaning up after a leak is on Battery Explosion, Capacitor or Corrosion Damage.

The values are not the same on every board, so they are not restated here. Sega's own parts list and console5's independent board-read agree position for position on the VA0 PAL board, which is about as good as corroboration gets for a thirty-year-old machine.

The CD block

This is the part that fails most often, and most of what circulates about "adjusting the laser" on a Saturn is wrong.

What Sega actually says.

• The wear indicator is the RF level at the RF test point, with a disc playing: it should be 0.8 to 1.4 Vp-p. Below 0.8 Vp-p the pickup is worn out and should be replaced.
• Do not turn the variable resistor on the pickup's APC board. Sega sets it at the factory, states that it cannot be adjusted in the field, and warns that adjusting it may destroy the laser diode. If the output is low, the diode is worn and the pickup is finished. There is no "turn it up" repair.
• After fitting a new pickup, forcing the door-close detection switch on should light the laser for about three seconds while the objective lens moves up and down.
• The four adjustments that do exist need an oscilloscope and an A-BEC TCD-792A test disc: R114 sets FE bias to 0 V at test point FE IN in stop mode, R111 sets focus gain to −7 mV playing track 1, R104 sets FE balance to 0 V at the centre of the waveform at BP IN, and R113 sets tracking gain to 0.4 V amplitude. They interact, so expect two or three passes.
• Out-of-specification focus gain stops the disc spinning at one extreme and causes skipping and noise at the other; out-of-specification tracking gain makes the drive shock-sensitive at one extreme and makes the lens oscillate at the other.
• Laser safety. When it is necessary to confirm beam emission, observe from more than 30 cm from the surface of the objective lens. Assembled, the console is a Class 1 laser product; with the interlock defeated there is invisible laser radiation.

Before any of that: clean the lens and check that the sled moves freely on its rails. A dirty lens and hardened grease account for a large share of "the laser is dead" machines.

Several different CD-ROM boards were fitted — JVC EXL-P604, EXL-P605 and ENR-007 B/D, Hitachi JA00292 and Sanyo CDK94V5SGC — so parts are not interchangeable between machines without checking.

Backup battery

Saves and the clock run from a CR2032 cell, in a holder behind its own lid on the underside of the case. Sega's accessories list gives it as "Lithium Battery (CR2032)" with the note "Positive Side B". Lost saves and a reset clock mean a flat cell. Replace it with the machine unplugged, and check the holder and surrounding board for corrosion while it is open.

Connectors

Oxidation and cracked joints account for most intermittent faults on a machine this old:

• the multi-AV connector — wiggling the lead should not disturb the picture;
• the controller ports, especially if a 3D Control Pad or a wireless receiver misbehaves while an ordinary pad is fine. console5 records voltage drops at the ports on VA0 to VA0.8 boards with higher-current peripherals, and the fix is a jumper from the port Vcc pins to a nearby Vcc point;
• the cartridge slot for memory and RAM carts;
• the ribbon between the CD drive and the main board;
• the mains inlet and the power switch.

Clean with isopropyl alcohol and reseat. If a connector's joints are cracked, reflow them rather than adding more contact cleaner.

Cooling

The Saturn cools passively. Keep the vents clear and do not run it in a closed cabinet. Sega's operating range is 5 to 35 °C at 10% to 80% RH, non-condensing.

Preventive schedule

1. Check the rails at the main board connector after any long period in storage.
2. Clean the cartridge slot, controller ports and AV connector annually.
3. Replace the CR2032 when saves start to go.
4. Inspect the power board's capacitors, and replace them if they show any sign of age.
5. Clean the lens and check the sled rails when read errors appear — before assuming the pickup is dead.
6. Leave clearance around the vents.

Related pages

• Sega Saturn (Model 1)
• Sega Saturn (Model 1) Troubleshooting Guide
• Sega Saturn (Model 1) Capacitor Replacement Guide
• Sega Saturn (Model 2) Maintenance Guide
• Capacitor Failure Symptoms
• Recommended Tools
• Retrobrite