Nanao MS9-29

Nanao (1994)

A 29" monitor featured in many machines, including the Sega New Astro City and Taito Egret II, in addition to many dedicated machines.

The biggest feature this monitor has over the MS8-29 is a unified Contrast adjustment, which adjusts gain of all three channels in unity. In addition, changing gain will not offset the bias level, so color tracking is not distorted in proportion to the bias levels.

This monitor supports 15KHz and 24Khz horizontal refresh rates.

B+ Voltage


The main DC supply voltage, B+, can be checked using the TP2 test point. It is located in the center of the PCB, in the corner of the "U" shaped side of the heatsink next to the empty inductor location L505.

The correct B+ voltages are:

Factory Bodges


'Rev. D "05A00585D1'

Known Games🔗

No known games for this hardware.

Known Parts🔗

Images and Diagrams🔗

Repair Manuals🔗

Repair Tips🔗

Pincushion and horizontal width adjustments do not work 🔗

Test or replace the transistor at Q508, which is a 2SD1944.

"Dead" 🔗

If it's dead, and the fuse at F901 is good, then your problem lies in the primary power supply. Almost always this is a defective MOSFET at Q901.

If Q901 has a silicone insulator around it, it is a Toshiba 2SK1531. Otherwise, it is a K1723.

Chirp, minutes after powering it down 🔗

If a monitor is dead, or has shut off, you may hear a chirp minutes after removing power from the chassis. This is the protection of the primary power supply being removed. this is a hint to check the primary power supply transistor at Q901.

Poor horizontal linearity 🔗

Horizontal S correction is provided by a switchable set of S-capacitors. A jumper labeled "E" connects to either CN507 ("Normal") or CN505 ("Wide"). This jumper connects or disconnects C531.

Horizontal blurriness, or trailing RGB lines 🔗

If a recap and adjustment of the focus knob on the LOPT doesn't make the image sharp, and you're sure it isn't the tube's condition, the video amp at U201 may need to be replaced. This is an M51387P.

MS9 shotgun chip repair list 🔗

Replacing these chips might be a good move in desperation if a solution has not presented itself.

  • Power MOSFET: either 2SK1531 in silicone sleeve or 2SK1723 with mica insulator @ Q901
  • HOT: 2SC4692 @ Q506
  • Diode: ESC021 @ D502
  • Width / pincushion amp: 2SD1944 @ Q508
  • 12V supply for RGB amp, etc: LM7805 @ U951
  • RGB Amp: M51387P @ U201
  • H-size IC: AN5551 @ U450
  • Synchronization IC: LA7853 @ U550
  • Vertical deflection IC: LA7838 @ U401

Heater Circuit and resistor 🔗

The heater resistor limits current going to the heater filament, which is on pins 9 and 10. As the filament can also be modeled as a resistor, the polarity is unimportant, and DC or AC voltage may be used. As the name suggests, it heats up.

Like many tubes, the A68KJU96X is designed to have a heater voltage of 6.3V. This voltage is a function of the resistance of the heater filament as well as the current-limiting resistor.

The heater resistor for the MS9-29 is located at R532, and is tucked between the LOPT (Flyback) and the heatsink.

On the MS9-29N22, MS9-29T, and other submodels that are intended for use with the A68KJU96X tube, the heater resistor is a 3.3 ohm resistor.