Sega Dreamcast Troubleshooting Guide

Sega's Dreamcast block diagram, sheet 7-1. The power supply and its 3.3 V, 5 V and 12 V outputs are at the bottom left, with the two core regulators beside them.

Fault-finding for the Sega Dreamcast, working from the supply inwards. Designators are from Sega's EU service manual, which covers the European VA1 boards 837-13820 and 837-13883, and from the VA0 schematic sheets hosted here; check which board you have before probing. Sega's EU manual lists a troubleshooting section in its contents but the binder does not contain it, so the symptom charts below are Sega's user-level chart from the US instruction manual plus measurements taken from Sega's diagrams.

First checks

Sega's own chart, from the US instruction manual, for faults that need no repair:

Sega's user troubleshooting chart (abridged)

Symptom	What Sega says to check
The Dreamcast is too hot to touch	Blocked air holes, the console sitting at an angle, a nearby heat source, and whether air comes out of the fan vent. If no air comes out, do not use it
The date and time screen appears at every power-on	The rechargeable battery has lost its charge. Leave the console on for at least two hours; if the screen still appears after that, the battery needs service
Does not turn on	The power cable, and that it is a Sega cable
A game does not start	The disc is seated label side up, clean and suitable for the console, auto start is on, and the lens is clean
The controller does not work	The controller is in a port, and the analog thumb pad and triggers were not touched while the power came on
No picture or no sound	The AV cable, the television input and volume

Sega also says not to touch the analog thumb pad or the triggers while switching on, because the controller is not initialised properly if they are touched.

Power

Warning: the supply carries mains voltage and its bulk capacitor stays charged after unplugging. Discharge it through a resistor and check with a meter before working on it.

Measure the three supply rails at the supply's output header CN3, then the two core rails on the logic board.

Rails and test points

Rail	Where to measure	Nominal
+12 V	CN3 pin 1 (GD-ROM drive)	12 V
+5 V	CN3 pin 5 (GD-ROM drive, controller ports, fan)	5 V
+3.3 V	CN3 pin 6 (logic board)	3.3 V
SH-4 core	IC104 pin 3 (input at pin 1)	1.95 V
HOLLY core	IC106 pin 3 (VDD at pin 2)	2.5 V or 2.7 V, depending on the IC106 part fitted

Sega gives nominal values only. If 3.3 V is missing, both core regulators lose their input and nothing on the logic board runs. If 12 V or 5 V is missing, the GD-ROM drive is dead.

On the supply schematic, the primary side runs from the mains inlet through fuse F1 (1.6 A), the common-mode chokes and the bridge RC1 to the bulk capacitor C3, the FA5317 controller M1, the MOSFET Q1 and transformer T1. Each of the three outputs then has its own rectifier and filter: C13 and C16 on 12 V, C17 and C20 on 5 V, C21 and C22 on 3.3 V. A blown F1 means something downstream has failed short; find it before fitting a new fuse. Sega's own repair centres replaced the whole supply. console5 lists the capacitors of each supply board; see Sega Dreamcast Capacitor Replacement Guide.

Reset

Sega's reset diagram says that SRST "becomes active after power has stabilized for a minimum of 300mS". SRST goes to HOLLY, which releases the SH-4 and sends GRESETN to the AICA, the GD-ROM decoder and the expansion connector. On the VA1 board the power-on reset delay is IC206, an RN5VD27A, with its output on pin 1 and its delay capacitor on pin 5. A console with good rails that never starts should be checked here and at the clocks before the large chips are suspected.

Clocks

X302, a 13.5 MHz crystal, drives the clock generator at IC305: a BU2179F on the VA0 schematic, a W129A on the EU VA1 boards. It produces 33.33 MHz for the SH-4 and the 54 MHz pixel clock for HOLLY. If X302 is not oscillating, neither processor runs.

The AICA's master clock input, CK33, is 33.8688 MHz, and it clocks the sound SDRAM at 67.7376 MHz. Its real-time clock runs from X301 at 32.768 kHz.

Video

HOLLY sends 24-bit RGB and sync to the video encoder IC401, a BU1426KS (Sega part 315-6145), which drives the AV connector CN602.

• No picture and no sound with the power LED lit: check the rails and reset first.
• No picture, sound present: check the AV cable, then CN602's solder joints, then IC401 and its output network.
• Picture lost when the cable is moved: reflow CN602.

Audio

The AICA (IC301; 315-6119 on VA0, 315-6232 on the EU VA1 boards) sends digital audio to the DAC at IC303, then through the op amp IC304 (NJM2100M) to the AV connector. On the VA0 schematic, CE303 and CE304 on the op amp inputs are bipolar electrolytics, and CE305 and CE306 (22 µF 6.3 V) are in series with the two outputs after the op amp.

• No sound, picture fine: the AV cable, then the AICA's 33.8688 MHz clock, then IC303 and IC304.
• One channel missing or distorted: CE305 or CE306, and the AV connector joints.
• Distorted or weak sound on both channels: the electrolytics of the audio circuit, CE301 to CE306 and CE308 to CE310. CE307 is on the supply pin of the clock generator IC305, not in the audio path.

GD-ROM drive

The drive is a CAV mechanism running from 4× to 12×, fed from 12 V and 5 V.

GD-ROM faults

Symptom	Check
Nothing moves	12 V and 5 V at CN3, then the drive cable
Spins but does not read	The lens (clean it), the disc, then the sled
Spins but the sled does not move	The gear train. console5 hosts a guide to fitting replacement spur gears

Sega's EU manual gives the drive as a complete unit, 610-6923-02 (Yamaha) or 610-7292 (Samsung), and has no adjustment procedure for it.

Controllers

The four controller ports are on sub board 2, which connects to CN601 on the main board through a 20-way flat cable. All four ports take their 5 V supply through F1 on the sub board, a 0.39 Ω fuse resistor (KOA RF25SCVTP, Sega 514-5109).

• All four ports dead: F1 on the sub board, then the flat cable and CN601.
• One port dead: that port's contacts and its signal lines on the sub board and through the filters FL601 to FL608 on the main board.
• A VMU with flat cells still works as a memory card, but beeps when the console is switched on.

IC locations

EU VA1 main board ICs (Sega parts list and IC specifications)

Position	Part	Sega's description
IC101	SH-4	Main CPU
IC102, IC103	64 Mbit SDRAM	Main memory
IC104	PQ07VZ1H2Z	Series regulator, 3.3 V to 1.95 V
IC105	TC7W241FU or SN74AHC2G241	CMOS 3-state buffer
IC106	RN5RG25A	CMOS voltage regulator, 3.3 V to 2.5 or 2.7 V
IC201	315-6201, 315-6225 or 315-6226	HOLLY graphics engine
IC202 to IC205	16 Mbit SDRAM	Texture and frame buffer
IC206	RN5VD27A	Power-on reset delay
IC301	315-6232	AICA sound processor
IC302	16 Mbit SDRAM	Sound memory
IC303	PCM1725, or 315-6262 (PCM1722U) on 837-13883	Audio DAC
IC304	NJM2100M	Op amp
IC305	W129A	Clock generator
IC401	BU1426KS	Digital RGB TV encoder
IC501	MPR-21931	Boot ROM, 16 Mbit
IC502	MBM29LV002	Flash

Things that are not faults

• The date and time screen at every power-on: a flat clock cell. See Sega Dreamcast Maintenance Guide.
• A beep at power-on: a VMU with flat cells in a controller.
• Analog stick or triggers misbehaving after they were touched at power-on: switch off and on again without touching them.

Related pages

• Sega Dreamcast
• Sega Dreamcast Maintenance Guide
• Sega Dreamcast Capacitor Replacement Guide
• Sega Dreamcast VA0 Schematics
• Capacitor Failure Symptoms