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Sega Mega Drive / Genesis (Model 1) 32X Clock Modification

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Sega Mega Drive M5 PAL main board
A PAL Mega Drive main board, "IC BD M5 PAL", silkscreened for IC4 315-5402 (VA5) or 315-5433 (VA6). The 68000 (IC1) is at the top, IC4 and FB7 in the middle (photo: Bill Bertram, CC BY-SA 3.0)

Some Sega Mega Drive / Genesis (Model 1) boards make a Sega 32X shake, slow down or lock up. Between December 1994 and April 1995 Sega's Quality Assurance Division issued three service bulletins that cure this with changes to the console board: bulletins 008 and 012 for the VA4 board and bulletin 014 for the VA6.0, VA6.5 and VA6.8 boards. Sega traced the faults to the shape of two clock signals on the console board, EDCLK and VCLK, and each fix removes or changes capacitors on those lines.[1][2][3] ConsoleMods documents the same work as a step-by-step procedure, with the VA4 fixes applying to Asian and PAL VA4 consoles and the VA6 fix to VA5 and its sub-variants in all regions.[4]

Symptoms

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  • With a 32X fitted, the picture drawn by the 32X shakes, game sound slows down, and the game freezes. On a VA4 PAL board Sega says this starts once certain ICs and capacitors warm up at room temperature.[1] ConsoleMods reports that it can take up to an hour to appear, and that the console's own picture elements stay steady while the 32X layer jitters.[4]
  • Lock-ups with the 32X on a VA4 board (bulletin 012), or with some 32X units on a VA6.0, VA6.5 or VA6.8 board (bulletin 014).[2][3]

The same 32X working on another console points to this fault. Faults inside the 32X itself, a dirty cartridge slot or the 32X's flat cables give similar symptoms and are covered in the Sega 32X Troubleshooting Guide and the Sega Mega Drive / Genesis (Model 1) Troubleshooting Guide.

Identify the board

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The modification differs by board, so identify the board before starting. Sega's repair procedure names the custom chip at IC4 for each board version: 315-5364 on VER.4, 315-5402 on VER.5 and 315-5433 on VER.6.[5] The board photographed above is printed with both VA5 and VA6 part numbers beside IC4.

Which bulletin applies
Board IC4 Bulletins
VA4 315-5364 008 (EDCLK) and 012 (VCLK); Sega says 008 also helps the lock-ups that 012 cures[2]
VA5, VA6.0, VA6.5, VA6.8 315-5402 (VA5), 315-5433 (VA6) 014 (VCLK)[3][5]

Tools and parts

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  • Cross-head screwdriver, soldering iron, solder, flux, flush cutters, wire strippers, tweezers and desoldering braid. ConsoleMods lists leaded solder and recommends flux.[4]
  • Hook-up wire. For the VA4 ground jumper Sega asks for wire slightly heavier than AWG28 (0.38 mm diameter).[1]
  • For bulletin 008, a 33 pF ceramic capacitor for C92.[1] The C112 removed in the same bulletin is a 33 pF ceramic, and ConsoleMods reuses it at C92.[4][6]
Parts touched by the bulletins, from Sega's parts lists
Board Part As fitted Change
VA4 C92 51 pF 50 V ceramic, leaded (151-0072)[6] Replace with 33 pF ceramic next to IC4[1]
VA4 FB7 Ferrite bead between IC8 and IC4, above OSC1[1] Remove and bridge[1]
VA4 C112 33 pF 50 V ceramic, leaded (151-0020), added on the back at C19[6][1] Remove
VA4 C78 33 pF 50 V ceramic chip (151-5025)[6] Remove[2]
VA4 C100 33 pF 50 V ceramic, leaded (151-0020)[6] Remove[2]
VA6.5 C78 33 pF 50 V ceramic chip, 2125 size (151-0318)[7] Remove and jumper the pad to IC1 pin 15[3]

ConsoleMods describes C78 as a 1206 chip; Sega's VA6.5 list gives the 2125 (0805) size.[4][7]

Procedure

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Removing the main board

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Sega's procedure for the PAL-G console. Screw 201 is a 3 × 10 mm tapping screw, 202 a 3 × 8 mm tapping screw, 203 a 3 × 6 mm Deltite screw and 204 a black 3 × 12 mm tapping screw.[8]

  1. Turn the console over and remove the six screws (201) from the bottom case.[8]
  2. Lift the top case and unplug the two-pin connector from the power LED lead on the underside of the top case.[8] ConsoleMods notes that the LED leads are usually bent over and may need straightening, and that the connector at the board end is soldered to the board.[4]
  3. Remove seven screws (202) and one screw (203), and lift off the shield plate.[8]
  4. Remove one more screw (202) and the five black screws (204), and lift the main board out of the bottom case.[8] Keep the long screws apart from the others; ConsoleMods warns that a long screw in the wrong hole damages the bottom case. On non-Japanese consoles, pull the power jack board out of its screw boss first.[4]

VA4 boards: bulletin 008

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Sega 32X service bulletin 008 Mega Drive VA4 drawing
Sega's drawing for bulletin 008: (1) C92 next to IC4 and (2) FB7 on the front of the VA4 board; (3) C112 at C19 and (4) the jumper from C10 to EM16 on the back
  1. Turn the board over and remove C112, a 33 pF ceramic added on the back of the board and connected to the top of C19. Keep it if you plan to reuse it at C92.[1][4]
  2. On the back of the board, solder a jumper from the top of C10, which Sega says is electrically the same point as IC4 pin 31, to ground. Sega recommends the middle pin of EM16, one of the line filters for controller port 1, and wire heavier than AWG28.[1][4]
  3. Turn the board right side up. Remove FB7, the ferrite bead directly above the master clock oscillator, and bridge its two pads with wire or a component lead.[1][4]
  4. Replace C92, the 51 pF capacitor on the left side of IC4, with a 33 pF ceramic. Sega says the capacitor must sit next to IC4.[1][4]

VA4 boards: bulletin 012

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Sega 32X service bulletin 012 Mega Drive VA4 drawing
Sega's drawing for bulletin 012: C100 and C78 on the rear (termination) side of the VA4 board
  1. Remove C78 and C100.[2] ConsoleMods places C78 near the centre of the board and C100 below the cartridge port, and removes C78 by loading both pads with solder and heating them together, without bridging the pads.[4]
  2. Carry out bulletin 008 as well if it has not been done.[2]

VA5 and VA6 boards: bulletin 014

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Sega 32X service bulletin 014 Mega Drive VA5 VA6 drawing
Sega's drawing for bulletin 014, solder side of the VA5 and VA6 board: C78 removed and a jumper from its pad to pin 15 of the 68000
  1. Remove C78 from the board.[3] ConsoleMods sweeps it off by loading both pads with solder and heating them together.[4]
  2. Solder a jumper from IC1 pin 15 to the signal side of the empty C78 pad.[3] ConsoleMods identifies this as the topmost pad of C78 and pin 15 as the 68000's clock input.[4]
  3. Route the wire round the cartridge port pins, not between them. ConsoleMods found that the cartridge port support in the bottom case can crush a wire routed through the pins.[4]

Reassembly

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Sega's assembly procedure:[8]

  1. Set the main board on the bottom case with its screw holes over the case's, and fit the five screws (204) and the one screw (202) that hold it. Sega's assembly page prints "Fix 8 screws (202)" at this step; its disassembly steps and reference list account for one here and seven on the shield plate, eight in all.
  2. Fit the shield plate over the bosses of the bottom case, then the screw (203) and seven screws (202). Seat the headphone and AC adaptor sub boards on their bosses.
  3. Set the volume knob to 0 and the power switch knob on the top case to off.
  4. Reconnect the power LED lead, with the LED's longer lead (anode) to the red wire, and fit the top case.
  5. Turn the console over and fit the six screws (201).

Testing

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  1. Run the console with the 32X and a 32X game. ConsoleMods tests for at least an hour so that the board reaches full temperature before closing the case for good.[4]
  2. Check that the 32X picture no longer shakes, game sound keeps its speed and the game does not lock up.[1][2][3]
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References

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  1. ↑ 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., Quality Assurance Division, Service Bulletin No. 008, "Mega Drive 1 VA4 - PAL", 13 December 1994: subject, reason, the four-step EDCLK modification and the attached drawing (PDF pp. 1-2 of File:Sega 32X Service Builletins.pdf). See Sega 32X Service Bulletins.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Sega Enterprises, Ltd., Quality Assurance Division, Service Bulletin No. 012, "MD 32X / MD 1 (VA4)", 28 March 1995: lock-ups traced to the VCLK signal, removal of C78 and C100, and the instruction to perform the VA4 screen-shake modification as well (PDF pp. 5-6 of File:Sega 32X Service Builletins.pdf).
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Sega Enterprises, Ltd., Quality Assurance Division, Service Bulletin No. 014, "32X / MD1 (VA 6.0, 6.5, 6.8)", 12 April 1995: lock-ups traced to the VCLK signal; remove C78 and add a jumper from IC1 pin 15 to the signal side of the C78 pad; solder-side drawing captioned for MD1 VA5 and VA6 (PDF pp. 7-8 of File:Sega 32X Service Builletins.pdf).
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 "Genesis:32X Service Bulletin Fixes", ConsoleMods Wiki (revision of 2 June 2025, retrieved 25 October 2026): which boards and regions each fix applies to, materials and tools, disassembly notes, component locations, reuse of C112 at C92, wire routing round the cartridge port and the one-hour test. Community guide, CC BY 4.0.
  5. ↑ 5.0 5.1 Mega Drive Maintenance Manual, PAL-G, Sega Enterprises, August 1992, Rev. A, section 5 "PCB Repair Procedure", IC4 part numbers by board version (PDF p. 31). See Mega Drive Maintenance Manual - PAL-G, August, 1992, Rev. A.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Mega Drive Maintenance Manual, PAL-G, August 1992, section 8-1, parts list IC-BD M5 VA4 PAL-G: C78 33 pF chip (PDF p. 88); C92 51 pF, C100 33 pF and C112 33 pF leaded ceramics (PDF p. 95).
  7. ↑ 7.0 7.1 Mega Drive Maintenance Manual, PAL-G, August 1992, section 8-1, parts list IC BD M5 VA6.5 PAL-G, 837-8779, chip parts: C78 151-0318, CAP CER CHIP 33 pF 50 V CH 2125 (PDF p. 103).
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Mega Drive Maintenance Manual, PAL-G, August 1992, section 2-1 general reference number list (PDF p. 7) and "Procedure of Disassembly and Assembly" (PDF pp. 18-19).
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