Sega Saturn (Model 2) Troubleshooting Guide
Component-level fault-finding for a later Sega Saturn — the second-generation case, board revisions from about VA6 to VA15. Designators move between revisions on this machine more than on most, so check the silkscreen before probing anything.
First, the power
[edit | edit source]The Saturn has no external PSU, no DC adaptor and no barrel jack. It is mains-powered: the PAL machine is model MK-80200-50, rated AC 220–240 V at 50/60 Hz and drawing approximately 20 W, with a detachable mains lead and a switching supply module mounted inside the case.[1]
If a guide tells you to expect +9 to 10 V DC from an external PSU at the main board input, it is not describing this console. There is no such input.
Before the case is open: the supply's bulk capacitor holds charge after the lead is pulled — 200 V or 400 V rated depending on the module — and the mains tracks beside it are live whenever the console is plugged in.[2] Discharge it through a resistor and verify with a meter.
Rails
[edit | edit source]| Rail | Feeds | If it is missing |
|---|---|---|
| +9 V | CD drive, and the PLL | No disc activity; and with the PLL down, no clocks at all |
| +5 V | Every chip except the SDRAM | Nothing works |
| +3.3 V | SDRAM | The machine will not run, and the SDRAM is the first thing to check on a later board, where it has its own LVCC supply separate from Vcc[3] |
There is no +12 V rail on a Saturn and no negative rail. Sega publishes no tolerance band for these three, so none is quoted here; measure against the nominal figures and treat a rail that is visibly low or noisy on a scope as the fault.
The FUSE position is not a fuse
[edit | edit source]On VA0 PAL boards Sega's own parts list fills the position silkscreened FUSE with a jumper wire — part 600-6458, "JUMPER WIRE L=10MM".[1] console5 records the same thing from the other direction: many early boards were assembled with a jumper there and zero-ohm resistors in place of the ferrite beads.[2]
So there is no "internal fuse F1, 1.5 A fast-blow" to replace, and a continuity reading across that position proves nothing about the supply. If you have a later board with an actual fuse fitted there, read what is printed on it rather than assuming a rating.
Likewise there is no 7805 on a Saturn main board. The three rails come from the supply module, not from linear regulators on the logic board.[1]
| Symptom | Likely cause | Action |
|---|---|---|
| Nothing at all — no LED, no drive | Mains lead, wall socket, power switch, or the supply module | The lead is detachable and they do fail. Then the switch, then the supply |
| Power LED lit, no picture, no chime | A rail down, or the machine is not leaving reset | Measure +5 V, +9 V and +3.3 V at the main board connector |
| LED flickers, or the machine resets | Ageing capacitors on the supply board, or cracked joints | Recap the supply; reflow its joints |
| Works cold, fails warm | Marginal supply | Same. This is the classic ageing-supply symptom and it is not a CPU fault |
Picture faults
[edit | edit source]The Saturn's only video output is the multi-AV connector, and the part that drives it is IC21, a CXA1645M RGB encoder — not a VDP.[1]
| Symptom | Where to look |
|---|---|
| No picture, no sound, LED lit | The rails first, then the PLL at IC20 (315-5746), which is fed from the 14.318 MHz reference |
| No picture through one cable, fine through another | The cable. PAL machines shipped with an RGB lead;[1] a no-picture or wrong-colour symptom through a lead of uncertain provenance is a cable fault until proved otherwise |
| Picture cuts out when the lead is moved | The AV connector's own solder joints |
| Corrupt graphics, checkerboard patterns | Video RAM. On a VA0 board that is IC12, IC13, IC15 and IC16 — 2 Mbit SDRAM, not 256 kbit SRAM[1] |
| No colour or wrong colour | IC21 and the network around it |
The chip map is revision-specific
[edit | edit source]This is the single most common way to waste an evening on a Model 2 Saturn: taking an IC map from one board and probing another.
| Position | VA0 | Note |
|---|---|---|
| IC1, IC2 | HD6417095F28, the two SH-2 CPUs | On the VA13 sheets IC1 and IC2 are still the two SH-2s, IC2 marked 315-0998 |
| IC3, IC4, IC11 | 4 Mbit SDRAM, work RAM | On VA13 these are on a separate LVCC supply |
| IC5 | 315-5688, the SCU | On VA13, IC5 is a Yamaha 315-5966 — a different device in the same position |
| IC7 | EPR-17933 / MPR-17933, the IPL ROM | PAL part. Not "IC8" |
| IC9 | 315-5744, the SMPC | The controller ports run through this |
| IC10 | 315-5689 / 315-5883, VDP1 | |
| IC14 | 315-5690 / 315-5890, VDP2 | |
| IC17 | 315-5687, the SCSP sound processor | The sound chip is here, not at "IC13" |
| IC18 | MC68EC000FN12, the sound CPU | |
| IC20 | 315-5746, the PLL | Fed from 14.318 MHz |
| IC21 | CXA1645M, the RGB encoder | Not "IC14" |
| IC25 | S-80741AL, a voltage detector | This is the supervisor, not an MB3771 |
There is no security or region chip in this machine. Region is set by the IPL ROM fitted at IC7, which is why a PAL machine carries EPR-17933 and an NTSC one does not.[1] A Saturn that plays audio CDs but refuses an import game is working exactly as built.
CD faults
[edit | edit source]Most Saturn faults end up here, and most of the folklore about fixing them is wrong.
Sega's own figures.[1]
- RF level at the RF test point, with a disc playing: 0.8 to 1.4 Vp-p. Below 0.8 Vp-p, the pickup is worn 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. There is no "nudge the trimpot clockwise" repair on this machine, and doing it to a worn pickup finishes it.
- The four real adjustments — R114 FE bias, R111 focus gain, R104 FE balance, R113 tracking gain — need an oscilloscope and an A-BEC TCD-792A test disc, and they interact.
- After fitting a new pickup, forcing the door-close detection switch on should light the laser for about three seconds while the lens moves up and down. That is the quickest test that the new pickup is alive.
- Laser safety. Observe from more than 30 cm from the objective lens when confirming emission. With the interlock defeated there is invisible laser radiation.
| Symptom | Likely cause | Action |
|---|---|---|
| Nothing happens with the lid shut | Door-close detector, the drive's connectors, or the +9 V rail | Test the switch, reseat both connectors and the flat cable, measure +9 V |
| Spins, seeks, never reads | Dirty lens, hardened sled grease, or a worn pickup | Clean the lens, free the sled, then check RF level against 0.8–1.4 Vp-p |
| Reads audio CDs but not games | Almost always region, not hardware | The IPL ROM at IC7 decides this |
| Skipping, or noise | Focus or tracking gain out of specification, or a worn pickup | See the adjustment list above — with the right instruments, or not at all |
| Drive from another Saturn behaves differently | Different assembly | JVC, Hitachi and Sanyo drives were all fitted[2] |
Controllers
[edit | edit source]The ports run to the SMPC at IC9.[1] If controllers work intermittently, or a 3D Control Pad or wireless receiver misbehaves while an ordinary pad is fine, measure the supply at the port before replacing the pad: console5 records voltage drops at the ports on VA0 to VA0.8 boards with higher-current peripherals, fixed by jumpering the port Vcc pins to a nearby Vcc point.[2]
Saves are lost
[edit | edit source]The backup RAM is 256 kbit, held up by a CR2032 cell — Sega's accessories list gives the part as "Lithium Battery (CR2032)".[1] A machine that forgets its saves and its clock needs a cell, not a board repair. Check the holder for corrosion while it is open.
Capacitors
[edit | edit source]Later Saturn boards use through-hole electrolytics; the earliest use surface-mount parts. Both leak with age, and leakage causes distorted or absent audio, video noise, random resets and discs that will not read. Designators are CE, not C.
Lists by board revision are on Sega Saturn (Model 2) Capacitor Replacement Guide and, for the surface-mount boards and the supply and drive boards, Sega Saturn (Model 1) Capacitor Replacement Guide. Two positions to be careful with: CE45 and CE46 differ between revisions — 330 µF and 330 µF on the earliest boards, 330 µF and 220 µF on VA1, 220 µF and 330 µF from VA6 onwards.[2]
Things that are not faults
[edit | edit source]- Playing ordinary audio CDs. It is a CD player as well as a console.
- Stopping when the lid opens. The door-close detector doing its job.
- Refusing an import disc. The IPL ROM, working as built.
- No ACCESS light. The second-generation case deletes it.[4]
- An empty FUSE position on an early board. It is a jumper by design.[1]
Related pages
[edit | edit source]- Sega Saturn (Model 2)
- Sega Saturn (Model 2) Maintenance Guide
- Sega Saturn (Model 2) Capacitor Replacement Guide
- Sega Saturn (Model 1) Troubleshooting Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Sega Enterprises, Ltd., Service Manual — Sega Saturn (PAL), No. 013-1, June 1995 — hosted on this wiki as File:Sega service manual - sega saturn pal - no. 013-1 june 1995.pdf (see Sega Service Manual - Sega Saturn Pal - 1 June 1995). Section 1 gives the ratings (model MK-80200-50, AC 220–240 V 50/60 Hz, approximately 20 W, 5–35 °C and 10–80% RH non-condensing, 260 × 230 × 83 mm) and the specification (two 32-bit RISC SH2 at 28.4 MHz, 68EC000 at 11.3 MHz, work RAM 16 Mbit, video RAM 12 Mbit, sound RAM 4 Mbit, CD buffer RAM 4 Mbit, IPL ROM 4 Mbit, backup RAM 256 kbit); section 3 the accessories (lithium battery CR2032, RGB cable, AC cables for the UK, SOE and Australia); section 5 the disassembly; section 6 the CD drive maintenance and adjustment figures including the 0.8–1.4 Vp-p RF level and Sega's warning against adjusting the APC variable resistor; section 7 the block diagram with the +9 V, +5 V and +3.3 V rails; and section 11-3 the electrical parts list for the VA0 main board, which fills the position silkscreened FUSE with jumper wire 600-6458.
- ↑ 2.0 2.1 2.2 2.3 2.4 console5 TechWiki, Saturn, https://wiki.console5.com/wiki/Sega_Saturn . Secondary source — per-revision capacitor lists read off real boards covering VA0 through VA15, the power supply units by manufacturer and model (Fujitsu, Panasonic, Phihong, Voltek and Yamaha, with 200 V or 400 V primary-side bulk capacitors), and the CD-ROM PCBs. Its VA0 PAL list (837-11491 / 837-11493) agrees position for position with the parts list in Sega's own PAL service manual. Also the source for CE45 and CE46 being 330 µF and 330 µF on the earliest boards, 330 µF and 220 µF on VA1 and 220 µF and 330 µF from VA6 onwards; for the controller-port voltage drop on VA0 to VA0.8 boards with higher-current peripherals and the jumper-wire fix; for the assembly of many early boards with a jumper in place of the fuse and zero-ohm resistors in place of the ferrite beads; and for the several CD-ROM boards fitted across the range — JVC EXL-P604, EXL-P605 and ENR-007 B/D, Hitachi JA00292 and Sanyo CDK94V5SGC.
- ↑ 3.0 3.1 Sega Saturn VA13 Service Manual (PAL) — hosted on this wiki as File:Sega Saturn VA13 Service Manual PAL.pdf (see Sega Saturn VA13 Service Manual (PAL)). A partial scan, redrawn and watermarked by a third party: an overall block diagram giving a 28.6 MHz 32-bit clock and a 14.318 MHz PLL reference, eleven main-board schematic sheets and power supply and CD unit sheets. It carries no parts list. Sheet 1/11 shows IC1 and IC2 as the two Hitachi SH-2 devices, IC2 marked 315-0998, with IC3 and IC4 as 4 Mbit SDRAMs on a separate LVCC supply and a per-device bypass capacitor block; sheet 2/11 shows IC5 as a Yamaha 315-5966, a different part from the 315-5688 in the same position on the VA0 board.
- ↑ Sega Saturn, Sega Retro. Secondary source. Source for the HST-3220 second-generation case, released in Japan on 22 March 1996, and for the statement that "the only feature omitted is the 'Access' LED seen in previous models".