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Sega Master System II Video Output Repair

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Sega Master System II video output schematic
Sega's video encoder circuit for the PAL board 171-5922A. Composite video leaves IC9 (CXA1145P) on pin 20 and passes through R21, C38 (100 µF) and bead FB5 to the RF modulator's video input, with R29 to ground on the modulator side of C38; audio leaves pin 9 through R28 and FB6 to modulator pin 3

Most Sega Master System II consoles have only an RF output.[1] On Sega's PAL schematic the video processor's RGB output goes through a resistor network and the coupling capacitors C27, C28 and C29 to the RGB inputs of IC9, a CXA1145P encoder, on pins 2, 3 and 4. Composite video leaves IC9 on pin 20 and passes through R21, the electrolytic C38 (100 µF) and bead FB5 to the RF modulator's video input, pin 2; R29 runs from the modulator side of C38 to ground. Audio leaves IC9 on pin 9 and reaches modulator pin 3 through R28 and bead FB6. The modulator takes its 5 V on pin 1 from the VDD rail through bead FB4, and its case is ground.[2][3]

When there is no picture, the first cause Sega lists is "C38, R29 is absent or faulty", followed by soldering, a cut track, the RF modulator, IC9 and the parts around IC9.[4] The procedure below follows the composite signal from the modulator back to IC9 and replaces the failed part.

Symptoms

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  • Sound but no picture on the television.[4]
  • No picture and no sound, a dirty picture, or a lot of audio noise: Sega lists the RF modulator, its supply and IC9 for these.[4]
  • Abnormal colours: Sega lists IC9.[4]

Faults that look similar:

  • Nothing at all, with no 5 V: the supply. See Sega Master System II Power Regulator Replacement.
  • A black screen on RF with the supply good and no sound either: the console may not be running. Check the reset circuit and the clocks in the Sega Master System II Troubleshooting Guide.
  • The French console (model 3006-09) has no RF modulator and no composite output; it gives RGB through an eight-pin DIN socket, so a composite lead shows no picture. On SMS Power's forum, an owner of a 3006-09 who saw a black screen on a composite lead was told that the console is RGB only and needs Sega's RGB adapter.[5][6]

Tools and parts

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  • Oscilloscope to see the video signal, and a multimeter.
  • Phillips screwdriver.[1]
  • Soldering iron, desoldering pump or braid; a high-powered iron if the RF modulator has to come out.[1]
  • An electrolytic capacitor for C38: 100 µF, 10 V or higher (Sega part 150-0047, 100 µF 10 V; Wilson fitted a 16 V part).[3][1]
  • Resistors for R21 and R29 if they have failed, of the value for your board (see the table).
Video output parts on the PAL board
Position Value on most boards PAL-B (VE) board (Australia) Where it sits
R21 2 kΩ 75 Ω IC9 pin 20 to C38
C38 100 µF 10 V electrolytic Not given separately R21 to FB5
R29 2.2 kΩ 33 Ω Modulator side of C38 to ground
FB5 Bead inductor FBA04 – C38 to RF modulator pin 2
FB4 Bead inductor FBA04 – VDD to RF modulator pin 1

Values from Sega's PAL parts list and the notes on the schematic. On the drawing the note markers *1 and *2 sit against the opposite resistors to the ones the notes name; the parts list agrees with the wording of the notes.[3][2]

Procedure

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Narrow it down from outside

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  1. Tune the television to the console's channel. Sega's product table gives the RF channel for each regional model, for example channel 36 for the German PAL-G console and 0 or 1 for the Australian PAL-B console.[7]
  2. Try another RF lead and, if one is fitted, another switch box. Sega lists a cut or shorted cable, a faulty plug, the soldering at the cable terminals and the switch box itself as causes of no picture.[4]
  3. Listen for sound. Sound with no picture points at the video path below; no picture and no sound points at the modulator, its supply, or a console that is not running.[4][2]

Open the console

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  1. Unplug the adaptor, the RF lead and the controllers, and remove any cartridge.
  2. Turn the console over, remove the five Phillips screws around the edge of the bottom case, and lift the board out of the case and its shielding (five screws around the edge, two at the regulator, two each side of the cartridge port on Wilson's board).[1]
  3. Find the RF modulator, C38, R21, R29 and IC9 at the top left of the board on Sega's parts-location drawing. C38 sits between the modulator and IC9, with R21 beside IC9.[8]
Sega Master System II M4 Jr PAL-G parts location
Sega's parts-location drawing for the PAL-G board. The RF modulator is at the top left, with C38, FB5, FB4 and R21 between it and IC9 (CXA1145P)

Follow the signal

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With the board connected to the adaptor and the television, switched on and running a game, work back from the modulator:

  1. Measure the modulator's supply on pin 1: 5 V. Sega's RF modulator check asks whether +5 V is present. If it is missing, check FB4 and the VDD rail; see Sega Master System II Power Regulator Replacement.[4][2]
  2. Look for video at the modulator's video input, pin 2, to ground. Sega's list says pin 3, which is the audio input on the schematic.[4][2]
  3. If there is video at pin 2 and 5 V at pin 1 but no picture, Sega's remaining cause on this side is the RF modulator itself.[4]
  4. Look for video on each side of C38. Video on the R21 side and none on the FB5 side means C38 is open. Video on the FB5 side and none at modulator pin 2 means FB5 or the track.[2]
  5. A signal that is present but very small on the FB5 side of C38 points at R29 or something shorting that node to ground. Switch off and measure R29 with one end lifted.[2][3]
  6. Look for video at IC9 pin 20. Video there and none on the R21 side of C38 means R21 or its joints.[2]
  7. If there is nothing at IC9 pin 20, check IC9's supply, 5 V on pins 12 and 19 with pins 1 and 24 at ground, and the RGB signals arriving at pins 2, 3 and 4. Sega's list gives the RGB inputs as pins 1 to 4 and the video output as pins 19 and 20; on the schematic pins 1 and 19 are ground and supply. Sega also lists the parts around IC9; its location drawings show a factory jumper wire on the solder side joining C39 to IC9's ground, so check that it is present. With good inputs and supply and no output, IC9 has failed.[4][2][8]

Repair

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  1. Switch off and unplug.
  2. Replace C38 with a new 100 µF electrolytic of 10 V or more, fitted the same way round as the original. On Sega's schematic its positive side faces R21 and IC9.[3][2]
  3. Check R21 and R29 out of circuit against the values in the table, and replace either if it is open or far off.[3][2]
  4. Reflow cracked joints and repair cut tracks along the path; Sega lists both.[4]
  5. If the modulator has failed, replace it with one for the same television system; Sega's parts list gives 200-5091-A for PAL-I, 200-5198 for PAL-B (VE) and 200-5086 for PAL-G. Wilson found that removing the modulator needed a high-powered iron because of its thermal mass.[3][2][1]

On SMS Power's forum, a member advising on a Master System II with no video reported that replacing the coupling capacitor on the composite line from pin 20 of the CXA1145P sometimes cures it; on Sega's PAL board that capacitor is C38. The same member said that some models have a fuse between the supply and the encoder; none appears in Sega's PAL or RGB parts lists.[6][2][3][5]

Reassemble

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Refit the board in the bottom case with its screws and shielding, then the bottom case and its five screws.[1]

Testing

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  • A stable colour picture and clean sound on the console's RF channel.[4][7]
  • 5 V on modulator pin 1 with the console on.[4][2]

Revision notes

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The circuit and values are from Sega's documents for the PAL board 171-5922A; the PAL-B (VE) board for Australia uses 75 Ω at R21 and 33 Ω at R29.[2] Sega's no-picture check list keeps pin numbers that do not match the CXA1145P on its own schematic (video at modulator pin 3, RGB on IC9 pins 1 to 4, video out on pins 19 and 20); work from the schematic.[4][2] The French RGB board (171-5926A) has no RF modulator and is not covered here.[5] Later boards, such as 171-6395A, are not in the 1991 manual; check the positions on your own board, and see Sega Master System II for the board list.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Adam Wilson, "1992 SEGA Master System II Restoration & Modification", Adam's Vintage Computer Restorations, 13 February 2024: in most regions the Master System II has only an RF output; the bottom case is held by five Phillips screws around its edge (the sentence begins "The Game Gear is easy to dismantle", evidently a slip in an article about the Master System II); the main board is held into the bottom case and the RF shielding by five Phillips screws around its edge, two on the voltage regulator and two on each side of the cartridge port; removing the original RF modulator needs a high-powered soldering iron because of its thermal mass; on an early PAL board marked 171-5922-A the author fitted C38 as a 100 µF 16 V part.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 Sega Enterprises, Ltd., Sega Master System II Service Manual, April 1991, schematic diagram for the PAL version, "IC BD M4JR PAL" 171-5922A. Sheet 3 (p. 13, PDF p. 20): AV[0..4] through R12 to R18 and C27, C28 and C29 (0.1 µF) to IC9 (CXA1145P) RIN, GIN and BIN on pins 2, 3 and 4; SYNCI pin 10; AUDIOI pin 8 through C31 (1 µF); VIDEO pin 20 through R21 (*1), C38 100 µF (positive towards R21) and FB5 (FBA04) to RF MOD pin 2 VIDEO; R29 (*2) from the junction of C38 and FB5 to ground; AUDIOO pin 9 through R28 8.2 kΩ (C40 0.1 µF across it) and FB6 to RF MOD pin 3 AUDIO, R27 10 kΩ to ground; RF MOD Vcc (VRF) on pin 1, ground on the case; VDD through FB4 to VRF; notes "*1: R-29 is 33 ohms for PAL-B (VE), 2.2 Kohms for other versions" and "*2: R-21 is 75 ohms for PAL-B (VE), 2 Kohms for other versions". Sheet 1 (p. 11, PDF p. 18): bypass capacitor C54 0.1 µF for IC9, Vcc pins 12 and 19, ground pins 1 and 24. Hosted on this wiki as File:Sega Master System II Service Manual April 1991.pdf.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Sega Enterprises, Sega Master System II Service Manual, April 1991, parts list for the PAL version (pp. 19 to 21, PDF pp. 13 to 15): IC9 313-5067 CXA1145P; C38, C42 and C43 150-0047 100 µF 10 V; R21 479-0202 2 kΩ; R18, R20 and R29 479-0222 2.2 kΩ; R27 10 kΩ; R12, R14, R16 and R28 8.2 kΩ; C27, C28, C29, C39, C40 and C54 0.1 µF; FB1 to FB6 bead inductors FBA04; RF modulators 200-5091-A UB3622 (I-PAL), 200-5198 VE3423 (B-PAL VE) and 200-5086 UE3622 (G-PAL); 610-5128 RF switch box with RF cable.
  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 Sega Enterprises, Sega Master System II Service Manual, April 1991, repair procedures, pp. 3 to 10 (PDF pp. 5 to 12). RF modulator check (p. 5): is +5 V present; faults cut track, soldering, RF modulator, IC9; symptoms no picture, picture dirty, no sound, much audio noise. Symptoms by fault (p. 6): a faulty IC9, which converts the RGB signal to composite, gives no picture, or abnormal colour. "In event picture is not present" (p. 7): is video present at pin 3 of the RF modulator; is video output from pins 19 and 20 of IC9; is RGB present at pins 1, 2, 3 and 4 of IC9; faults C38 and R29 absent or faulty, soldering, cut track, RF modulator, IC9, peripheral parts around IC9. Auto switch boxes (p. 10): no picture, game picture or TV picture does not appear, from a cut or shorted cable, faulty plug, soldering at the cable terminal, broken track or faulty switcher; bad sound or audio noise from a cracked cable, soldering, plug connection or switcher.
  5. ↑ 5.0 5.1 5.2 Sega Enterprises, Sega Master System II Service Manual, April 1991, parts list for the RGB version (pp. 25 and 26, PDF pp. 16 and 17), PCB 171-5926A: CN5 212-5106 DIN connector; RGB box France 610-0130; no RF modulator. Product table (p. 1, PDF p. 3): France, MK-3006-09, PAL, RGB, RF modulator none.
  6. ↑ 6.0 6.1 SMS Power! forums, "No video on Master system II", February 2017: a Master System II with a black screen and good sound, model 3006-09; replies by Neto: some models have a fuse between Vcc and the CXA1145P encoder; "Sometimes just replacing the coupling capacitor on composite video line connected to pin 20 of CXA1145P after a 75R resistor solve this"; the 3006-09 has no composite video output, is RGB only, and needs the "Adapteur R.V.B." model 3085.
  7. ↑ 7.0 7.1 Sega Enterprises, Sega Master System II Service Manual, April 1991, product number and colour specifications (p. 1, PDF p. 3): RF modulator and channel by territory: Canada MK-3006-22 PAL B (VV) 200-5194-02 channel 3/4; Australia MK-3006-03 PAL B (VE) 200-5198 channel 0/1; New Zealand MK-3006 PAL D 200-5139 channel 2/3; China MK-3006-15 PAL G 200-5086-02 channel 3/4; Germany MK-3006-18 PAL G 200-5086-02 channel 36; France MK-3006-09 RGB, no RF modulator.
  8. ↑ 8.0 8.1 Sega Enterprises, Sega Master System II Service Manual, April 1991, parts location drawing "IC BD M4JR PAL-G" 837-7367 (p. 15, PDF p. 22), with sister drawings for the other regional boards on PDF pp. 21 to 26. The PAL drawings show a detail of the solder side with the note "Connect C39 and GND for IC9 with jumper wire as above". Hosted on this wiki as File:Sega Master System II M4 Jr PAL-G parts location.png.
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