Repair: Sanwa monitors (Sanwa Denshi)¶
Sanwa Denshi (Japan) — one of the major suppliers of CRT chassis for Japanese cabs (alongside Nanao and Toei). The PM series (PM-1723, PM-1745…), the 20I16 and 27Z21 chassis, and the tri-sync 29" 29E31S. Standard CRT repair: HV discharge, recap (fold-over / black bars = symptoms of dead caps), reflow, HOT/flyback.
Identification / range¶
| Chassis | Type | Sizes | Sync | Note |
|---|---|---|---|---|
| PM-1723 (B / C / D) | raster | ~20" | 15 (/24) kHz | cap kit = PM-1723 B/C/D and Sega 200-5090 / 20V21S |
| PM-1745 | raster | ~25" | 15/24 kHz | ≈ Nanao MS8/MS9, Rodotron 666a, Wei-Ya 2931a |
| 20I16DU | raster | ~20" | 15 kHz | dedicated cap kit (Nichicon 105 °C) |
| 27Z21-C | raster | 27" | 15/24 kHz | shares cap kit with PM-1745 |
| 20V21S | raster | 20" | 15 kHz | = Sega 200-5090 |
| 29E31S | tri-sync | 29" | 15/24/31 kHz | tri-sync candy cabs; ≈ Wei-Ya 2929/2931a |
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¶
| Symptom | Likely cause | Lead |
|---|---|---|
| Fold-over / black bars | dead electrolytics | Recap (classic Sanwa/Sanyo symptoms) |
| No picture / no HV | HOT, flyback, +B supply | Check HOT / flyback / +B |
| Intermittent dropouts | cold solder joints | Reflow |
| Image shrinks / jitters | dried caps (recap) | Recap |
| Won't lock at 31 kHz (29E31S) | tri-sync switching / sync | Check sync + detect stage |
| Blur | flyback focus | Adjust / replace flyback |
Repair (method)¶
- HV discharge → CRT safety.
- Recap (method) — per-series cap kits; ⚠️ the big filter is not in the kits (e.g. 680 µF/250 V on the PM-1723D) → separately. Cross-check against your board (B/C/D revisions).
- Reflow the joints (neck, flyback, connectors).
- HOT / flyback, focus / geometry adjustments.
Equivalents (chassis swap)¶
Per Arcade Otaku: PM-1745 ≈ Nanao MS8/MS9, Rodotron 666a, Wei-Ya 2931a, Neotec 2702; 29E31S ≈ Wei-Ya 2929 / 2931a. A beyond-repair chassis can be replaced by an equivalent — check tube/yoke and frequencies.
Cap kits & parts¶
- arcadepartsandrepair — PM-1723D · PM-1745 · 20I16DU (Nichicon 105 °C).
- ⚠️ Big filter separately; cross-check against the board.
See also¶
- Nanao MS8 / MS9 / MS29xx tri-sync · Wells-Gardner · Sanyo 20-EZ · Hantarex · Modern tri-sync · CRT safety · Recap.
Sources & attribution¶
- arcadepartsandrepair — Sanwa PM-1723D / PM-1745 / 20I16DU cap kits (series, separate filter) — https://www.arcadepartsandrepair.com/
- Arcade Otaku Wiki — Monitor Chassis Equivalents (PM-1745 ↔ Nanao/Rodotron/Wei-Ya; 29E31S ↔ Wei-Ya) — https://wiki.arcadeotaku.com/w/Monitor_Chassis_Equivalents
- Museum of the Game — Sanwa 29E31S & fold-over/recap logs — https://forums.arcade-museum.com/
- Sanwa Denshi — service manuals (PM / 29E31S) — to reference
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.
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