Sega Master System Capacitor Replacement Guide
Capacitor replacement for the Sega Master System (model 1, the "Power Base"). The model 1 was built on several main boards for NTSC, PAL and Japanese markets, and their electrolytic lists differ. Identify the board before ordering parts.
Sega's service manual has a complete parts list for the PAL "PC Main M4" board. console5 has board-read lists for the other revisions.[1][2]
Identify the board
[edit | edit source]| Board | Region | Source |
|---|---|---|
| 837-6097, IC Board PB PAL-G | Spain, Italy, West Germany, Holland | Sega[3] |
| 837-6118, IC Board PB PAL-B | Australia | Sega[3] |
| 837-6135, IC Board PB PAL-I | UK, Hong Kong | Sega[3] |
| 837-6067 (171-5378) | NTSC | console5[2] |
| 837-6405 (171-5532) and 837-6629 | NTSC, later | console5[2] |
| 837-6148, IC Board M4J Main | Japan | console5[2] |
| Power Base PAL VA3 | PAL, late | console5[2] |
Signs of failure
[edit | edit source]See Capacitor Failure Symptoms. On this board look for bulging or leaking cans, residue or corrosion around the pads, and video or audio noise. Measure the 5 V rail and the adaptor before blaming the capacitors.
PAL "PC Main M4" board: Sega's list
[edit | edit source]Sega numbers the board in one sequence across component types (C1, C2, C3, C4, R5, C6, D7, R8 and so on), and the part number gives the type: 150- parts are electrolytics and 151- parts ceramics. The list has fifteen electrolytics, all U-type.[1]
| Position | Value | Sega part |
|---|---|---|
| C1 | 10 µF 16 V | 150-0023 |
| C4 | 100 µF 10 V | 150-0047 |
| C6 | 4.7 µF 16 V | 150-0007 |
| C25 | 100 µF 10 V | 150-0047 |
| C28 | 100 µF 10 V | 150-0047 |
| C30 | 47 µF 10 V | 150-0062 |
| C48 | 10 µF 16 V | 150-0023 |
| C119, C120, C121 | 10 µF 16 V | 150-0023 |
| C122, C123, C124 | 47 µF 10 V | 150-0062 |
| C131 | 10 µF 16 V | 150-0023 |
| C137 | 10 µF 16 V | 150-0023 |
C1 sits after the power switch at the input of the 7805. The schematic in the same manual, which is for the IC Board PB PAL VA1 (171-5534), marks it 100 µF 16 V, and console5 gives 100 µF 16 V for the NTSC 837-6629.[4][2] Fit what your board is marked for. The same schematic shows a 1 µF electrolytic, C51, on the encoder's audio input, which the parts list does not have.[4]
Other boards: console5 lists
[edit | edit source]| Value | 837-6067 (171-5378) | 837-6405 (171-5532), 837-6629 |
|---|---|---|
| 10 µF 16 V | CA1, C1, C49, C119, C120, C121, C131 | None |
| 10 µF 10 V | None | CA1, C49, C119, C120, C121, C131 |
| 100 µF 16 V | None | C1 |
| 100 µF 10 V | CA20, C4, C20, C22, C25, C28 | C4, C20, C28, C51 |
| 47 µF 10 V | C122, C123, C124 | C122, C123, C124 |
| 1 µF 50 V | None | C37 |
| Value | 837-6148, Japan (IC Board M4J Main) | Power Base PAL VA3 |
|---|---|---|
| 220 µF 10 V | C1 | None |
| 100 µF 16 V | None | C50 |
| 100 µF 10 V | C4, C20, C41, C42, C43, C44, C45 | C53, C54, C63, C72 |
| 47 µF 16 V | None | C9, C10, C11 |
| 47 µF 10 V | C122, C123, C124 | None |
| 10 µF 16 V | C30, C47, C131, CCP1, CCP2 | C1, C70, C71, CP, and up to six marked "CE" |
| 2.2 µF 50 V | C22, C24, C26, C27, C28, C29, C46 | None |
| 1 µF 50 V | None | C62 |
console5 calls the Japanese board "an outlier", with a very different set of capacitors from every other Master System.[2] Do not recap it from an export list.
console5's "CP" entry for the Power Base PAL VA3 is not backed by a Sega list. In Sega's list for the PAL PC Main M4 board both CP positions are ceramic capacitors,[1] and on the Master System II Sega's CP positions are 0.022 µF ceramics (see Sega Master System II Capacitor Replacement Guide). Check the part fitted at CP before ordering an electrolytic for it.
Procedure
[edit | edit source]- Unplug the adaptor. Remove the case screws and lift the top case. West German consoles have a bottom shield plate (250-5022) that other markets do not.[3]
- Photograph the board and compare it with the parts location drawing.
- Desolder each capacitor with a pump or wick, letting the pads cool between attempts.
- Clean the pads with isopropyl alcohol.
- Fit 105 °C radial capacitors of the same value and at least the same voltage, observing polarity.
- Check for bridges and reversed parts, then run the checks below before closing the case.
Tools are covered on Recommended Tools.
Checks after the recap
[edit | edit source]Sega's service figures for this board:[5]
| Check | Where | Expected |
|---|---|---|
| AC adaptor | Adaptor plug, no load | 13 V ± 1 V |
| Regulator input | IC8 (7805) input | DC 9 V |
| Regulator output | IC8 output | DC 5 V |
| Reset | Test point JR | Rises slowly from 0 to 3.6 V; if not, check C131 and R130 |
| CPU clock | IC5 pin 34 | 3.579545 MHz ± 30 Hz, 5 Vp-p (Sega's NTSC figure) |
| Video | CON1, no load | DC 1.3 V on the video pin; DC 1.9 V on the RGB pins 6, 5 and 8 |
| Audio | CON1 pins 1 and 2 | Up to 300 mVp-p, 20 Hz to 20 kHz |
If there is no picture after the work, Sega's first suspects are C28 and R27 on the composite output.[5] If the LED does not light, check IC8; Sega's causes include a faulty heatsink attachment.[5] The board has no fuse.[1]
Related pages
[edit | edit source]- Sega Master System (Model 1)
- Sega Master System General Maintenance
- Sega Master System Troubleshooting Guide
- Sega Master System II Capacitor Replacement Guide
- Capacitor Failure Symptoms
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Sega Enterprises, Ltd., Sega Master System Service Manual, pp. 19-21, "PC Main M4, Mark 4 Part List PAL Type". Hosted on this wiki as File:Sega Master System (Model 1) Service Manual.pdf.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 console5 TechWiki, "Sega Master System", retrieved 2026-10-01. Capacitor lists for the 837-6067, 837-6405/171-5532 and 837-6629 NTSC boards, the Japanese 837-6148 and the PAL VA3 Power Base.
- ↑ 3.0 3.1 3.2 3.3 Sega Enterprises, Sega Master System Service Manual, p. 18, Power Base parts list: IC boards 837-6097 (PAL-G), 837-6118 (PAL-B, Australia) and 837-6135 (PAL-I, UK and Hong Kong); top shield plate 250-5023; bottom shield plate 250-5022, West Germany only.
- ↑ 4.0 4.1 Sega Enterprises, Sega Master System Service Manual, pp. 13-14, schematic of IC Board PB PAL VA1, 171-5534 (PDF pp. 14-15): CON7, JV, power switch, C1 100 µF (16 V), C2 0.1 µF, IC8 7805 on a heatsink with silicone grease, C3 0.1 µF, C4 100 µF; C51 1 µF on the audio input of the CXA1145P at IC9.
- ↑ 5.0 5.1 5.2 Sega Enterprises, Sega Master System Service Manual, pp. 4-9 and 11: service procedures, fault tables and troubleshooting guide, and the AC adaptor check.