Sega Saturn (Model 1) Troubleshooting Guide

Sega's circuit board diagram for the 837-11493 VA0 PAL main board. The controller ports are along the bottom edge, and CE45 and CE46 sit beside the position marked FUSE at the lower left.

Fault-finding on the Sega Saturn Model 1 starts with the mains supply and its three rails, then follows Sega's block diagram. The designators are those of the VA0 PAL main board in Sega's service manual No. 013-1; later boards renumber some parts, so check the silkscreen first.

Power

The Saturn is mains-powered through a power supply inside the case; the PAL MK-80200-50 is rated AC 220-240 V, 50/60 Hz, about 20 W. Sega lists the supply as one part (400-5271 or 400-5272) with a 1.6 A fuse. The supply sends three rails to the main board at CN3:

Rail	Use on Sega's block diagram
+9 V	CD drive, and the PLL
+5 V (VCC, AVCC2)	All chips other than the SDRAM
+3.3 V (LVCC)	SDRAM

Warning: the supply's primary side is at mains potential and its reservoir capacitor can hold a charge after unplugging. Discharge it before working on the supply. Capacitor lists for the supplies are on the Sega Saturn (Model 1) Capacitor Replacement Guide.

The position silkscreened FUSE on the VA0 PAL main board is a 10 mm jumper wire (Sega part 600-6458), not a fuse. Console5 notes that many VA0 to VA0.8 boards were built this way.

Dead or no picture

Symptom	Check
No power lamp	Mains lead and socket; the power switch; the supply's fuse; then the supply itself. The power lamp is on the separate power indicator board (green LED LD1)
Power lamp lit, no picture	The three rails at CN3. Then the AV cable: UK and other European machines were supplied with an RGB cable and Australian machines with an RF unit
Rails present, still no picture	The clock: X1 (17.7344 MHz on the PAL board) into the PLL at IC20, which generates the CPU, sound and master clocks
Picture missing or wrong colour through a known-good cable	The RGB encoder IC21 (CXA1645M), which feeds the A/V OUT connector CN5
No reset, or reset does nothing	The reset button (SW1, on the R.SW board) and the Master Reset switch at the back (SW3, on the main board) are inputs to the SMPC (IC9), which drives the system resets

IC map

From Sega's electrical parts list for the VA0 PAL main board, with functions from the block diagram.

Position	Device	Function
IC1, IC2	HD6417095F28 or HD6417095SF28	Master and slave SH-2 CPUs
IC3, IC4	4 Mbit SDRAM	Work RAM high
IC31, IC32	4 Mbit DRAM	Work RAM low
IC5	315-5688	SCU, system control unit
IC6	315-5778	DCC, DRAM controller
IC7	EPR-17933 or MPR-17933	IPL ROM (PAL)
IC8	32K × 8 SRAM	Backup RAM
IC9	315-5744	SMPC: controller ports, resets, and the 32.768 kHz crystal X4
IC10	315-5689 or 315-5883	VDP1
IC11	4 Mbit SDRAM	VDP1 sprite RAM
IC12, IC13	2 Mbit SDRAM	VDP1 frame buffers
IC14	315-5690, 315-5690-02 or 315-5890	VDP2
IC15, IC16	2 Mbit SDRAM	VDP2 video RAM
IC17	315-5687	SCSP, sound processor
IC18	MC68EC000FN12	Sound CPU
IC19	4 Mbit DRAM	Sound RAM
IC20	315-5746	PLL clock generator
IC21	CXA1645M	RGB encoder
IC22	TDA1386T	Audio DAC
IC25, IC35	S-80741AL, S-80723AN	Voltage detectors
IC34	µPC78L05T or TA78L05F	5 V regulator

The CD subsystem is on the separate SH-1 board (838-10834): the SH-1 CPU at IC101, the 4 Mbit CD buffer DRAM at IC102 and the OCU gate array at IC103, with a 20 MHz crystal at X101.

CD faults

Sega's go/no-go test for the pickup is the RF level (eye-pattern amplitude) at the RF test point with a disc playing: 0.8 to 1.4 Vp-p is normal, and below 0.8 Vp-p the pickup should be replaced. Sega says the APC-board variable resistor on the pickup is set at the factory and must not be adjusted, as this may damage the laser diode.

Symptom	Check
Disc does not spin	Clean the lens. Focus gain (R111) set too low stops the lens focusing and the disc does not rotate
Skipping, more noise	Focus gain too high; or tracking gain (R113) too low, which also makes the drive sensitive to knocks and can stop the time counter
Unstable or distorted CD sound	Tracking gain too high, so the lens oscillates
Reads nothing after a pickup change	With the door-close switch held on, the laser should light for about three seconds while the lens moves up and down; then work through Sega's adjustments
Drive stops with the lid open	Normal: the lid has a detector switch (SPPB11)

The adjustment procedure (R114, R111, R104 and R113 with an oscilloscope and an A-BEC TCD-792A test disc) is on the Sega Saturn (Model 1) Maintenance Guide. Console5 lists several CD-ROM boards fitted across the range, from JVC, Hitachi and Sanyo.

When the beam has to be checked, Sega says to observe from more than 30 cm from the objective lens; there is invisible laser radiation when the console is open with the interlocks defeated.

Controller ports

The ports (CN2) connect to the SMPC at IC9. If a 3D Control Pad or wireless receiver misbehaves while an ordinary pad works, measure the supply at the port. Console5 records voltage drops at the ports of VA0 to VA0.8 boards with higher-current peripherals and fixes them with a jumper from the port Vcc pins to a nearby Vcc point; later boards deleted the port fuse and the ground ferrite beads.

Saves lost or clock reset

The 256 kbit backup RAM (IC8) and the clock are kept by a CR2032 cell (Sega part 401-0054), which the block diagram shows feeding the SMPC. Replace the cell and check its holder for corrosion. See Battery Refurbishment.

Capacitors

The VA0 board uses surface-mount chip electrolytics in the CE series. Leaking electrolytics can cause any of the faults above; see Capacitor Failure Symptoms and the full list on the Sega Saturn (Model 1) Capacitor Replacement Guide.

Related pages

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