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Repair: Nanao MS2930 / MS2931 / MS2932 / MS2933 (tri-sync)

The Nanao tri-sync family — the 31 kHz big brothers of the MS8/MS9. These 29" chassis accept 15 / 24 / 31 kHz (where MS8/MS9 stop at 15/24 kHz), hence their use in late tri-sync candy cabs (New Net City, Naomi Universal…). Repair is identical to MS8/MS9: recap, reflow, HOT/flyback.

Identification / family

Chassis Sync Note Compatibility
MS2930 15/24/31 kHz 29" ↔ MS2931 / MS2934 (compatible)
MS2931 15/24/31 kHz 29", Toshiba tube ↔ MS2930 / MS2934
MS2932 15/24/31 kHz 29", A68KJU96X tube (= MS9-29 / MS8-29 / D29CR55) tube shared with MS8/MS9
MS2933 15/24/31 kHz 29" = "bug-fixed" MS2931
MS2934 15/24/31 kHz 29" ↔ MS2930 / MS2931
  • vs MS8 / MS9: the MS8 and MS9 are 15/24 kHz; the MS29xx series adds 31 kHz (VGA / Naomi / Type X). The tube is the same Toshiba A68KJU96X as MS8-29/MS9-29 (handy for a tube donor).

Safety (read first)

High voltage — discharge the tube

Lethal high voltage held while unplugged → discharge the anode. See CRT safety & HV discharge. Isolation transformer for powered measurements.

Common faults

Identical to MS8/MS9 (same component families):

Symptom Likely cause Lead
No picture / no HV HOT, flyback, +B supply Check HOT / flyback / +B
Intermittent dropouts / flicker cold solder joints (neck, flyback, connectors) Reflow the hot spots
Image shrinks / jitters dried electrolytics (recap) Recap
Won't lock at 31 kHz tri-sync switching / sync stage Check incoming sync, the detect stage
Blur / washed-out colours flyback focus / neck board Adjust focus, diagnose the neck board

Procedure — working through a chassis ✅

Discharge the anode before anything else

The tube holds its charge with the cabinet unplugged, and so does the main filter capacitor. Discharge it, keep one hand in your pocket, and do not work on it alone. → CRT safety

Hot chassis: the ground is not earth

Some arcade chassis are referenced to the mains. On those, chassis ground is not earth, and an earthed oscilloscope clipped to it makes a dead short through your probe. Work through an isolation transformer. → CRT safety

1. Cold, before switching on. Cracked solder joints are the fault on these chassis — around the connectors, the flyback and anything heavy enough to work its own joints loose. Also swollen capacitors, cooked resistors, the brown halo of something that has been running hot. Reflow what looks suspect before diagnosing: a good share of intermittent chassis faults end there.

2. Fuse and primary side. A fuse that goes again is a short downstream, not a fuse problem — find it before fitting another.

3. Is there EHT at all? The tick of the flyback at switch-on, the filament glowing in the neck. No EHT points at the supply or the line stage. EHT but no picture points at video or the G2 — two very different jobs, and this is the measurement that separates them.

4. Recap — before any adjustment. This page carries the capacitor list — take the one matching your exact chassis if it covers more than one. On a chassis of this age recap is not optional: the electrolytics are thirty years old and have been running hot since day one. → Recap

5. Adjustments, and only now. ⚠️ Never before the recap. Setting the geometry of a chassis whose capacitors are dying records the drift and makes you do the whole job twice. Write down where every pot was before you touch it. → CRT safety

6. Scan rate. This page covers several chassis with different capabilities — take the line for yours from its table. A board whose rate the chassis does not accept shows nothing, and nothing is faulty.

7. Verification. Let it run warm for a good while and check the geometry stops moving. A chassis that is right cold and wrong after twenty minutes is still a thermal fault — usually a joint, sometimes a capacitor you left in.

Repair (method)

  1. HV discharge → CRT safety.
  2. Recap (method) — same procedure as MS8/MS9; cross-check the BOM against your board (revisions), the big filter is often outside the kit.
  3. Reflow the joints (neck, flyback, deflection connectors, neck board).
  4. HOT / flyback = wear; focus / screen (G2) on the flyback, geometry.
  5. Tri-sync: if 31 kHz won't lock, check the sync type and the frequency-detect stage.

Equivalents (chassis swap)

Per Arcade Otaku: MS8/MS9 ≈ Rodotron 666a / Wei-Ya 2931a / Neotec 2702; the MS2932 ≈ Rodotron 666b1 (untested against MS2930/MS2931). A beyond-repair chassis can be replaced by an equivalent — check tube/yoke and frequencies.

Cap kits & parts

  • Nanao MS9-29 cap kits (close) and Nanao flybacks from arcade vendors; read off your board for the exact MS29xx series.

See also

The values, surveyed board by board ✅

ⓘ MS-2933 and MS-2934 — this wiki now carries cap maps: location by location, the value and the voltage as a contributor read them off their own board. → MS-2933 and MS-2934

⚠️ This is not a manufacturer specification. A revision changes the list: read the can before you pull it, and where it disagrees with your board, your board is right. ⓘ A voltage the sheet does not give shows as —, never as a plausible number.

Sources & attribution

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.