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Repair: Nanao MS8 monitor

A Nanao colour CRT monitor chassis, fitted in Sega candy cabs (including the Sega Astro City). Dual-frequency 15/24 kHz. The #1 fault: tired capacitors → recap.

Identification

Field Value
Manufacturer Nanao (EIZO)
Type Colour CRT monitor chassis
Sizes MS8-26 (26"), MS8-29 (29")
Frequencies 15 / 24 kHz (auto-sync)
Cabinets Sega Astro City and other candy cabs

Level & risks
Difficulty Intermediate → Advanced
Risks CRT high voltage (lethal), fragile traces/joints
Time Recap: 2-4 h

High voltage — discharge the tube

A CRT holds very high voltage (~20-30 kV) even unplugged, for a long time. Discharge the anode (via a resistor to the chassis ground) before any work. Don't work alone if untrained.

Common faults

Symptom Likely cause Lead
Image shrinks / breathes / shakes Dried-out caps (power/deflection) Recap
No image (HV present) Caps, cold joints, flyback Recap + reflow, test flyback
Blurry image / lack of focus Focus adjustment, aging flyback Adjust focus; flyback if dead
Washed-out colours / shrinkage G2 (screen), caps Adjust G2; recap
Intermittent cut-outs Cold joints (flyback, deflection, connectors) Reflow the suspect points
Lines / fold Deflection stage, caps Recap; deflection diagnosis

Recap (the main repair)

The remedy for most faults on this chassis.

  1. Unplug, discharge the anode, remove the chassis.
  2. Photograph before removal (polarity/orientation).
  3. Replace the electrolytic capacitors with quality 105 °C equivalents, low ESR for the switch-mode power. Respect µF, V ≥ original, polarity.
  4. Check / reflow the joints around the flyback, deflection and connectors (classic hot spots).
  5. Adjustments: focus, screen (G2), geometry via the chassis pots.

Capacitor list — MS8-26SU ✅

Source: arcademonitor.com. 30 capacitors (+ a separate 680 µF / 200 V filter, generally not replaced). Shopping list:

Value Voltage Qty
1 µF 50 V 6
1 µF 100 V 1
4.7 µF 100 V 1
10 µF 25 V 1
10 µF 50 V 1
10 µF 100 V 1
10 µF 250 V 1
22 µF 160 V 2
33 µF 16 V 1
33 µF 100 V 2
47 µF 16 V 2
47 µF 25 V 1
47 µF 50 V 1
100 µF 50 V 1
100 µF 200 V 1
120 µF 50 V 1
220 µF 35 V 2
220 µF 50 V 1
470 µF 16 V 2
470 µF 50 V 1

Check the sub-model

This list applies to the MS8-26SU (26"). The Astro City often uses an MS8-29 (29"); other sub-models (MS8-25…) differ. Confirm the exact sub-model of your chassis (seller kit / schematic).

Per-reference list (C332 → C913) — expand

NB = neck board, VB = vert board.

Ref µF V Ref µF V
C332 (NB) 10 250 C537 4.7 100
C401 1 50 C561 10 100
C420 (VB) 1 50 C563 1 50
C422 470 50 C570 22 160
C431 33 100 C572 47 16
C432 33 100 C573 470 16
C433 10 25 C574 10 50
C437 120 50 C576 470 16
C451 100 50 C579 1 50
C452 1 100 C906 100 200
C454 47 50 C908 47 25
C501 1 50 C909 22 160
C521 33 16 C910 220 50
C522 47 16 C912 220 35
C532 (VB) 1 50 C913 220 35

→ Alternative kits: Console5 · arcademonitor.com

Verification

Stable image, correct geometry, sharp focus, no hot cut-out, colours OK.

Pitfalls & common mistakes

  • Forgetting to discharge the tube (danger + hardware risk).
  • Reversing the polarity of an electrolytic.
  • Neglecting cold joints: a recap alone won't fix a mechanical break.

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.

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