Sega Saturn (Model 1) Black Screen Repair

The main board of a Japanese HST-3200 Saturn (Model 1) in its bottom case, with the CD drive, the shielding and the power supply removed (photo: Evan-Amos, public domain)

A Sega Saturn (Model 1) with a black screen powers up, often with its power lamp lit, but shows no picture or a blank one. Repairers report many causes: a failed internal power supply, failed surface-mount electrolytics on the early main boards, a flat backup cell, corrosion under the chips, and faults in the custom chips themselves. The most discussed is the clock generator, the 315-5746 PLL at IC20, for which no replacement part was available when repairers reported the fault in 2023 and 2024. Two repairers have since found that the PLL itself was healthy and that the fault was in the capacitors around it.

The steps below follow the order those repairers use: supply rails, a visual inspection, the clocks out of IC20, the capacitors that feed and filter IC20, and then corrosion and solder joints. Designators are from Sega's PAL service manual for the VA0 PAL main board; a VA0.5 NTSC-J board and a PAL VA SD board described by the repairers cited here use the same numbers for the capacitors around IC20.

Symptoms

• The power lamp lights and the access lamp may flash, but the screen stays black.
• A picture that rolls, drops out or shows the wrong refresh rate, or a console that boots and later freezes, can come from the same clock faults.

Walter Comunello separates two cases. With a black screen, the RGB encoder (IC21, CXA1645M) still sends a signal the television can lock to, but there is no image in it, so the fault is in communication between the chips or in their clocks. With no display at all, the encoder sends nothing, which points to its supply or to the encoder itself. Try another AV cable before opening the console; see the Sega Saturn (Model 1) Troubleshooting Guide.

Safety

Warning: the Saturn's power supply is inside the case and its primary side is at mains potential whenever the console is plugged in; the PAL machine runs from AC 220-240 V. Its reservoir capacitor can stay charged after unplugging. Measure the rails with care and keep probes away from the supply board, and unplug the console before soldering.

Tools and parts

• A multimeter, and an oscilloscope for the clock checks. Without a scope, a video converter that reports the input refresh rate and sync lock, such as an OSSC, shows whether the clocks are stable.
• A temperature-controlled iron, hot air, flux, desoldering braid, 99.9% isopropyl alcohol and an ESD-safe brush.
• Fine wire for trace repairs: Adam Wilson used a single strand from multi-core cable because his thinnest wrapping wire was too thick.
• Capacitors for the PLL area, below.

Electrolytics around IC20 on the VA0 PAL board

Position	Sega's part	Where it sits on Sega's schematic
CE18	100 µF 6.3 V chip electrolytic (150-0313)	IC20's supply, fed from AVCC1 through the choke L5
CE19	100 µF 6.3 V chip electrolytic (150-0313)	IC20's supply, through the choke L3
CE20	10 µF 16 V chip electrolytic (150-0464)	The network on IC20 pin 23 (PDOUT1)
CE21	10 µF 16 V chip electrolytic (150-0464)	Beside C29 at the lower right of IC20
CE22	4.7 µF 25 V chip electrolytic (150-0496)	The network on IC20 pin 12 (PDOUT2)

Adam Wilson's PAL VA SD board has the same values at CE18 to CE22 in through-hole parts. On a VA0.5 NTSC-J board Walter Comunello fitted polymer tantalum capacitors at CE18 and CE19, tantalum at CE20 and CE21 and a ceramic at CE22.

The clock circuit

IC20 (315-5746) on Sega's VA0 PAL schematic, sheet 3/6: crystal X1 (17.7344 MHz on the PAL board), CE18 to CE22, the chokes L3 and L5, the DOTSEL input from the SMPC, and the outputs buffered by IC23 and IC24 (74VHC04) to the test points TP19, TP20, TP21 and TP84 to TP86

On Sega's schematic IC20 runs from crystal X1 (17.7344 MHz on the PAL board) and gives out the master and sound clocks. Its DOTCLK output (pin 18) passes through 74VHC04 inverters in IC23 to test point TP20 (MCLK0), and SNDCLK (pin 17) through IC24 to TP21 (SCSPCLK). Other outputs reach TP19 (MCLK1) and TP84 to TP86 (MCLK4 to MCLK2). DOTSEL, from the SMPC, selects the dot clock.

The area around IC20 on Sega's circuit board diagram of the VA0 PAL main board: CE18 to CE22, the unused crystal position X2, and IC7 below

Procedure

Open the console

1. Unplug the mains lead. Remove the six screws (A) and slide the top case off; Sega's Fig. 5-1 shows five in the base and one at the back. Adam Wilson counted five on the underside of his PAL Model 1.
2. Disconnect the CD drive's two connectors and flat cable and lift the drive out.

Check the supply

1. Plug in and switch on with the board in place. Measure the rails at CN3: Sega's block diagram labels them +9 V (CD drive and PLL), +5 V and +3.3 V (SDRAM). Sega gives no tolerances. On Adam Wilson's console all three were present and the fault lay elsewhere.
2. If a rail is missing, the supply needs repair first; see the Sega Saturn (Model 1) Capacitor Replacement Guide for its parts.

Look for damage

1. Inspect the electrolytics on the main board. On VA0 boards joostr14 found corrosion on the pads under the surface-mount capacitors, bad enough that they came away when touched, and the same corrosion on the pads of the RAM chips.
2. Inspect the pins of the large chips for green or blue corrosion. Adam Wilson found it on several pins of IC1, one of the two SH-2 CPUs.
3. Inspect the surface-mount inductors L1 to L10. iVirtualZero lists blown inductors among the black-screen faults he has repaired, and names L7 and L8 as the higher-powered ones. Sega's VA0 PAL list gives the chip coils at L1 to L6 and L8 to L10 as 100 µH parts.
4. Replace the CR2032 backup cell if it is flat; a dead cell is one of the simpler black-screen causes Adam Wilson lists.

Check the clocks

1. With an oscilloscope, look at DOTCLK at TP20 and the other clock test points. joostr14's advice is to check the clocks before anything else: clean, stable waveforms mean the PLL is not the fault.
2. Without a scope, feed the RGB output to a converter that shows the refresh rate and sync lock. An unstable rate points to the clocks.
3. Walter Comunello found extreme jitter on DOTCLK on a VA0.5 NTSC-J board with a black screen, and an unstable DOTCLK on another console.

Replace the capacitors around IC20

1. Unplug the console. On the first boards, including Sega's VA0 PAL, the CD subsystem is on a separate SH-1 board, which comes off first: remove the four screws and the top shield plate, then one screw, release three tabs and lift the board out.
2. Remove the four screws that hold the CD drive supports, then the five screws, and lift the main board out.
3. Replace CE18, CE19, CE20, CE21 and CE22 (table above). Observe the polarity marked on Sega's board diagram. joostr14 says the original capacitors now measure above 20 Ω ESR where they should be below 1 Ω, and recommends recapping before declaring the PLL dead.
4. Clean the pads with isopropyl alcohol before fitting the new parts. For leaked electrolyte see Battery Explosion, Capacitor or Corrosion Damage.
5. Refit the board and check the clocks again. On Walter Comunello's VA0.5 board the jitter had gone after these five capacitors were replaced, and the console booted to the clock-setting screen. joostr14 reports stable clocks after a recap on every one of ten consoles he worked on in two weeks.

Avoid heat on IC20 itself. iVirtualZero describes the 315-5746 as heat-sensitive and warns against soldering to or near it; he reports that a quick, light reflow of the PLL has revived some boards, but a reflow did not fix one of his and may have made it worse.

Repair corrosion and joints

1. Remove corrosion from chip pins and pads with tweezers, then 99.9% isopropyl alcohol and an ESD-safe brush. Tin the cleaned copper with solder to show up breaks in the traces.
2. Bridge any broken trace with fine wire, using leaded solder and flux paste, and clean the board again. On Adam Wilson's console two broken traces at IC1 were the whole fault: with them bridged, the console booted.
3. Reflow chips whose joints look dull or cracked. If the solder will not wet the pins, joostr14 lifts the chip, removes the old solder with braid, scrapes the oxide off the pads and solders it back; an active flux such as RA flux may let the pins reflow in place, but it is corrosive and has to be cleaned off completely.
4. Walter Comunello also refreshed the joints of the resistor arrays RA4 and RA5, between the SCU and the cartridge slot.

Testing

Checks after repair

Check	Where	Expected
Supply	CN3	+9 V, +5 V and +3.3 V present
Dot clock	TP20 (MCLK0)	Clean and stable on the scope
Video	RGB output	Stable refresh rate and sync lock
Boot	Power on with no disc	Picture; the console asks for the date and time if the cell was replaced
Soak test	Boot menu or a game	No freezes; Walter Comunello left his at the boot menu for an hour and power-cycled it

Revision notes

• Sega's VA0 board uses chip electrolytics, while Adam Wilson's PAL VA SD board has through-hole parts at the same positions. The Sega Saturn (Model 1) Capacitor Replacement Guide lists them by board revision.
• iVirtualZero gives the PLL on VA0 to VA5, and on the PAL VA9, as a 315-5746 (Hitachi HD49422), and on VA6 to VA9 Model 2 boards as a CY2292SC, which is still available.
• On two early Model 2 consoles with VA SD and VA SG boards, which he describes as essentially Model 1 boards in a Model 2 case, iVirtualZero found IC6 (315-5963) running hot on both black-screen units. See Sega Saturn (Model 2) Black Screen Repair.
• On one console Walter Comunello traced part of the instability to a damaged SMPC driving DOTSEL; swapping in an SMPC from another board, together with the other work, cured it.

Related pages

• Sega Saturn (Model 1)
• Sega Saturn (Model 1) Troubleshooting Guide
• Sega Saturn (Model 1) Capacitor Replacement Guide
• Sega Saturn (Model 1) Maintenance Guide
• Sega Saturn (Model 1) CD Drive Adjustment
• Sega Saturn (Model 2) Black Screen Repair
• Sega Service Manual - Sega Saturn Pal - 1 June 1995
• Battery Explosion, Capacitor or Corrosion Damage