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Sega Mega Drive / Genesis (Model 2) Maintenance Guide

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Sega Mega Drive II VA0 PAL main board parts location
Sega's component-location drawing for the PC BD MD2 VA0 PAL board (Mega Drive II, top view). The regulator IC12 and its heatsink are at the left, the cartridge connector CN3 runs across the middle and the expansion edge CN2 is at the right.

Routine care of the Mega Drive II / Genesis II (Model 2) is mostly cleaning, connector work and checking the adaptor. The board has one 7805 regulator, IC12, which supplies all the logic, and Sega's 1993 service manual and its two supplements document it down to component level.[1]

Power adaptor

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The Model 2 takes a centre-positive DC supply. On Sega's schematic the centre pin of the DC jack CN7 runs through the common-mode filter CF1, the power switch S2 and the diode D2 (1SR35-100A) to the reservoir capacitor CE16 (220 µF 16 V) and the regulator IC12; the sleeve is ground.[1] CN7 is an EIAJ-3 jack, Sega part 212-5353.[2]

Model 2 AC adaptors in Sega's accessories lists[2]
Machine Sega part Rating as listed
Genesis II (USA) 400-5135A (and -01 to -03) AC 120 V in, DC 10 V 0.85 A out
Mega Drive II, UK 400-5208 AC 240 V in, DC 9 V 0.85 A out
Mega Drive II, Australia and New Zealand 400-5211 AC 240 V in, DC 9 V 0.85 A out
Mega Drive II, other territories 400-5209 AC 230 V 50 Hz in, DC 10 V 0.85 A out

The Model 1 adaptor will not fit. Sega changed the DC jack from the Model 1's pin plug to the EIAJ-3 jack because the adaptor changed, and the Model 2 adaptor is rated 0.85 A against the Model 1's 1.2 A (Sega notes it is the same adaptor as the Master System II).[3] The Sega 32X uses the same EIAJ-3 jack part (212-5353), and Sega lists adaptor 400-5135A for the US 32X.[4]

Measure the adaptor with the console connected and switched on, not open-circuit.

Specification

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From Sega's ratings and specifications table.[5]

Item Figure
Power input Genesis II: AC 120 V 60 Hz. Mega Drive II: AC 220 V 50 Hz (PAL-I), AC 240 V 50 Hz (PAL-B), AC 220 V 50 Hz (PAL-G, RGB), as printed
Power consumption 18 W
Operating environment 5 to 35 °C, 20 to 80% RH, non-condensing
Dimensions 220 (W) × 212 (D) × 59 (H) mm
CPU 68000 (8 MHz) and Z80A (4 MHz)
RAM 72 kbytes
VRAM 64 kbytes
Colours 512
Video outputs Video and RGB
Slots Cartridge and extension

The Model 2 has no headphone socket, no volume control and no RF output or channel switch (both moved into the external RF unit). The power switch is a push-button; the Model 1 had a slide switch.[3] Sound and video leave through the 9-pin mini-DIN CN1.[1]

Disassembly

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Sega's procedure.[6] Screw 202 is a 3 × 10 mm tapping screw, 201 a 3 × 8 mm and 203 a black 3 × 16 mm.

  1. Switch off and turn the console over.
  2. Remove the four screws (202) and lift off the top case.
  3. Remove the nine screws (201) and the shield plate.
  4. Remove the two screws (203) and lift the main board out of the bottom case.

Reassembly:

  1. Fit the 64-pin cover, then put the main board into the bottom case and tighten the two screws (203).
  2. Refit the shield plate and tighten the nine screws (201).
  3. Turn off the power switch on the main board before attaching the top case. Sega calls it the tactile power switch.
  4. Fit the top case, engage it with the bottom case, turn the unit over and tighten the four screws (202).

Cleaning

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Case and buttons

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  • Wipe the shell with a damp microfibre cloth and mild detergent. Avoid abrasives.
  • Clean around the power and reset buttons with a cotton bud lightly moistened with isopropyl alcohol.
  • For yellowed plastics, see Retrobrite.

Cartridge slot and ports

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  • Blow dust out with dry air.
  • Clean the cartridge connector (CN3, a 64-pin edge connector) with a thin card wrapped in a lint-free cloth moistened with isopropyl alcohol.[2]
  • Clean the controller ports (CN5, a double D-sub 9 assembly) and the 60-pin expansion edge for the Mega-CD (CN2) the same way.[1]
  • A fibreglass pen will shift stubborn oxidation on an edge connector, but it also removes plating, so use it sparingly.

Inside

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  • Unplug the adaptor before opening the case.
  • Use dry air and an anti-static brush on the board and the shield.

Supply checks

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All the logic runs from IC12 (µPC7805HF or TA7805S). There is no 12 V rail. The unregulated line between S2 and D2 is labelled "+9V" on Sega's schematic.[1][2]

Point Expected Notes
CN7 centre pin The adaptor's DC output Sega puts test points on both input lines straight after the jack
After S2 The same, with the switch on Nothing here with the switch on points to S2, CF1 or CN7
CE16 positive Input less the drop across D2 The reservoir ahead of IC12
IC12 output (VCC1) 5 V CE17 (100 µF) sits on the output

IC12 has its own heatsink. It drops a 9 V or 10 V input to 5 V for the whole board, so it runs warm.

Video encoder types

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Sega fitted three different RGB encoders at IC11 and tells the engineer to identify the one on the board before using the schematics: type F is a Fujitsu MB3514PF-G-BND-EF (313-5232-A), type S a Sony CXA1145M-T6 (313-5213-A) and type SM a Samsung KA2195D (313-5236-A). The differences are shown in difference tables on the schematic and board drawings and in the remarks column of the parts list.[7] All PAL and RGB boards use the MB3514; the CXA1145M and KA2195D appear only on NTSC boards.[2]

The encoder type changes component values. CE14, for example, is 10 µF 16 V on NTSC-S and NTSC-SM boards and 220 µF 6.3 V on NTSC-F, PAL and RGB boards.[2]

Capacitors

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Sega numbers the electrolytics on this board in a separate CE series and the ceramic chip capacitors in a C series. The VA0 parts list has CE1 to CE32 with no CE13: 10 µF 16 V in most positions, 220 µF 6.3 V at CE12, 220 µF 16 V at CE16, CE14 dependent on the encoder, 100 µF 10 V at CE17 and CE23, and 47 µF 10 V at CE18, CE19 and CE24 to CE28. All carry Sega part numbers in the 150- series.[2] The VA1 board changes CE1 from part 150-0418 to 150-0023 (both 10 µF 16 V) and adds CE33, 47 µF 10 V, on PAL boards.[8]

On VA1 boards C1 (20 pF) and C4 (47 pF) and a 1 kΩ resistor in position C15 are fitted or left out according to which of the four FC1004 service parts is used at IC6.[8]

Full values by board revision are on the Sega Mega Drive / Genesis (Model 2) Capacitor Replacement Guide. See Capacitor Failure Symptoms before deciding that capacitors are the problem, and Battery Explosion, Capacitor or Corrosion Damage for cleaning up after a leak.

Board revisions

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Identify the board before ordering parts. The board name is printed beside the Sega logo (for example "PC BD MD2 VA0 PAL").

Change What Sega changed
VA0 to VA1 Board assemblies 837-9602 (USA) and 837-9603 (Europe) become 837-9793 and 837-9794. The two main-RAM chips IC2 and IC3 are replaced by one part at IC2 and IC3 is deleted; the two VRAMs IC7 and IC8 are replaced by one MSM54C864 (or equivalent) at IC7 and IC8 is deleted. CE1 changes part number and CE33 is added on PAL boards[8]
VA1 to VA3 (Genesis II) Board 837-9793 becomes 837-10150. The audio op-amps IC9 and IC10 are replaced by one Sega 315-5684 at IC9, the surrounding circuit changes and the board is made slightly smaller[9]

Sega's supplement No. 001-1 also gives a hot-air procedure for removing and refitting the flat-package ICs: hold the nozzle 1 to 2 mm from the chip, lift it with tweezers when the solder melts after 20 to 30 seconds, clear the pads with braid without pressing (the pattern lifts easily), tack the new chip at its four corners, solder, wash off the flux and check for bridges under a magnifier.[10]

Oscillator

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OSC1 is a 53.693175 MHz module (230-5053-01D) on NTSC boards and a 53.203424 MHz module (230-5058-01D) on PAL and RGB boards.[2] Check a suspect oscillator against the figure for your board.

Connectors

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Ref Part Function
CN1 Mini-DIN 9-pin, 212-5364 AV output: composite video, composite sync, RGB, mono and stereo audio
CN2 60-pin card edge on the board Expansion port for the Mega-CD
CN3 64-pin edge connector, 209-5061 Cartridge slot
CN5 D-sub 9-pin × 2, 209-5066 Controller ports 1 and 2
CN7 EIAJ-3 DC jack, 212-5353 Power input

Sources: Sega's parts list and block diagram.[2][1]

Clean and reseat these when a fault comes and goes with movement of a lead or cartridge, and reflow any cracked joints.

Maintenance checklist

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  1. Confirm the adaptor is a Model 2 type and measure it with the console running.
  2. Clean the cartridge connector, the controller ports and the expansion edge.
  3. Check IC12's output if the console resets or glitches.
  4. Inspect the CE-series electrolytics for bulging or leakage.
  5. Refit the shield plate with all nine screws after any work inside.
  6. Keep the console within Sega's operating range of 5 to 35 °C and 20 to 80% RH.[5]
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Sega Enterprises, Service Manual: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001, June 1993, section 4 "Block diagram" (p. 7) and section 5-4 "Schematic diagram-4" (p. 11). See Sega Service Manual - Genesis II / Mega Drive II - June 1993.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Sega Enterprises, Service Manual: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001, June 1993, section 8-3 "Electrical parts list" (pp. 29-36) and section 8-4 "Accessories/package list" (pp. 37-38). See Sega Service Manual - Genesis II / Mega Drive II - June 1993.
  3. ↑ 3.0 3.1 Sega Enterprises, Service Manual Supplement: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001-1, August 1993, p. 3, "Differences between Mega Drive and Mega Drive 2" and "Differences between Genesis and Genesis 2". See Sega Service Manual Supplement - Genesis II / Mega Drive II - August 1993.
  4. ↑ Sega Enterprises, Service Manual: Genesis 32X (VA0, VA1) / Mega Drive 32X, No. 012, June 1995: ratings table and electrical parts list (DC jack CN8, 212-5353; AC adaptor 400-5135A for the USA). See Sega Genesis 32X / Mega Drive 32X Service Manual.
  5. ↑ 5.0 5.1 Sega Enterprises, Service Manual: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001, June 1993, section 1 "Specifications" (p. 3). See Sega Service Manual - Genesis II / Mega Drive II - June 1993.
  6. ↑ Sega Enterprises, Service Manual: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001, June 1993, section 3 "Disassembly" (p. 6) and section 8-2 "Mechanical parts list" (p. 28). See Sega Service Manual - Genesis II / Mega Drive II - June 1993.
  7. ↑ Sega Enterprises, Service Manual: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001, June 1993, "Before using this service manual" (p. 2). See Sega Service Manual - Genesis II / Mega Drive II - June 1993.
  8. ↑ 8.0 8.1 8.2 Sega Enterprises, Service Manual Supplement: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001-2, December 1993, section 1-2 "Difference table and parts list" (p. 3). See Sega Service Manual Supplement - Genesis II / Mega Drive II - December 1993.
  9. ↑ Sega Enterprises, Service Manual: Genesis II VA3, No. 001-3, August 1994, preface and section 1 "Difference table" (p. 2). See SEGA Genesis Model 2 VA3 Service Manual.
  10. ↑ Sega Enterprises, Service Manual Supplement: Genesis II / Mega Drive II (PAL-B/I/G, RGB), No. 001-1, August 1993, pp. 8-9, "Flat package IC removal" and "Flat package IC installation". See Sega Service Manual Supplement - Genesis II / Mega Drive II - August 1993.
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