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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

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) — 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).
  3. Reflow the joints (neck, flyback, connectors).
  4. 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

See also

The values, surveyed board by board ✅

ⓘ PM-1745, 29E31S and PFX KW0606A — this wiki now carries cap maps: location by location, the value and the voltage as a contributor read them off their own board. → PM-1745, 29E31S and PFX KW0606A

⚠️ 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.