Sega Master System II Motherboard The Sega Master System II is a compact 8-bit home console released in 1990. Its simplified design—omitting the original power switch and reset button—makes it easy to overlook routine maintenance needs. This guide covers every recommended step to keep your SMS II running reliably for decades: mechanical care, electrical inspections, contact cleaning, capacitor health, and environmental best practices.
Soldering: 60 W temperature-controlled iron with conical tip; desolder braid & pumpMeasurement: ESR meter; digital multimeterCleaning: Isopropyl alcohol (≥ 90 %), DeoxIT D5 contact cleaner, compressed air, soft nylon brush, lint-free swabsMechanical: Nylon spudgers, plastic pry tools, light machine oil (e.g. Tri-Flow), cotton swabsReplacement Parts: 105 °C low-ESR electrolytic capacitors (Nichicon FR/Panasonic FC/Rubycon ZLJ), 2.1×5.5 mm PCB-mount power jack, plastic-safe grease
Always unplug the console and peripherals.
Discharge static by touching a grounded metal surface; use an ESD wrist-strap when handling PCBs.
Work in a well-ventilated area away from flammable materials.
Let soldering iron heat fully before use; avoid prolonged heating on PCBs.
Place console top-side down; remove six Phillips screws (4 in corners, 2 under cartridge tray).
Pry apart top and bottom shells at rear vent clips using a nylon spudger.
Lift out the cartridge tray assembly—no cables attached.
Unscrew the two RF-shield screws; hinge the shield upward and remove.
Slide the logic board forward to disengage front edge; lift straight out, noting AV-port cable orientation if fitted.
Wipe shell halves with a mild detergent solution; rinse and air-dry.
Blow out dust from ventilation slots using low-pressure compressed air.
Cartridge Tray Mechanism
Inspect the metal push-lock rails and springs. Lightly lubricate sliding surfaces with a plastic-safe grease.
Clean the tray surfaces and spring contacts with isopropyl alcohol to remove grime.
Controller ports: spray contact cleaner into each port; plug/unplug a controller several times.
AV-out DIN connector: clean pins with DeoxIT on a swab; avoid bending fragile contacts.
Power-jack socket: inspect for looseness; clean inner barrel with a cotton swab moistened in alcohol.
Visual Inspection
Look for bulging or leaky electrolytic capacitors on the logic board—especially C1–C4.
Inspect solder joints around power-jack, edge connector, RF shield posts, and VDP/PSG ICs for cracks or “white” oxidation.
SMS II Electrolytic Capacitors
Ref
Value
Voltage
Purpose
C1
100 µF
16 V
Z80 clock decouple
C2
47 µF
16 V
+5 V core rail smoothing
C3
10 µF
16 V
SN76489 PSG decouple
C4
4.7 µF
10 V
Audio output filter
Measure ESR for each cap; if > 1 Ω, install 105 °C, low-ESR replacements.
Desolder old parts cleanly, avoid pad lifting; scrub flux residue with IPA.
Power-Jack Replacement
If the external DC jack is loose or intermittent, desolder its three PCB pins and install a new 2.1×5.5 mm centre-positive jack.
Verify correct polarity and secure orientation before soldering.
Cartridge slot: apply DeoxIT to the edge connector; insert a donor PCB rom-edge, move in/out to polish contacts.
Test continuity between each pin of the slot and its corresponding IC to ensure no open circuits.
Solder Joint Reflow
Reflow any suspicious joints on the RF-shield grounding posts and the multi-layer cartridge connector.
Use a small amount of fresh lead-bearing solder to strengthen aged joints.
Although the Z80 and VDP run cool, ensure vents remain unobstructed to prevent heat buildup.
Avoid storing the console in enclosed or unventilated cabinets.
If operating in a warm environment (> 30 °C), provide additional airflow (small USB fan).
Recommended Maintenance Interval
Interval
Tasks
Every 6 months
Dust out vents; clean cartridge and controller ports.
Every 2 years
Inspect & clean inside; check caps ESR; reflow key joints.
Every 5 years
Replace electrolytic capacitors; replace power jack if needed.
As required
Lubricate tray rails; reseat ICs; clean A/V connector.
Store in a cool, dry location (15 – 25 °C; < 50 % humidity).
Keep cartridges and console covered to minimize dust ingress.
Use silica gel packs in storage containers to control moisture.
Remove power adapter when not in use to avoid creeping voltage stress.
