Philips NMS 8255 General Maintenance
.png)
The Philips NMS 8255 shares its main board, analogue unit and power supply with the Philips NMS 8250, so the full procedures for the shared parts (opening the case, the alignments, the service switch and the clock battery) are on Philips NMS 8250 General Maintenance.[1] The sections below cover what is particular to the two-drive machine and what NMS 8255 owners have reported.
Safety
[edit | edit source]The power supply board carries mains voltage: the line filter, the 2 A mains fuse F1001 and the transformer primary are on it, with the mains switch wired to it. An experienced forum member warns that parts of the NMS 8250/55 supply are not safe to touch.[2][3] Unplug the machine before opening it. Change cartridges only with the computer switched off.[4]
Dust and the supply rectifiers
[edit | edit source]On Wild_Penguin's NMS 8255 the rectifier diodes D1050 to D1053 had a coat of dust that he likened to a thermal insulator, and the board was darkened round them. Removing the dust and fitting new diodes reduced the brightness and sound level drift he had been seeing.[3]
- With the case open and the machine unplugged, look at the four diodes beside the 6.3 A fuse F1050 on the supply board.[2]
- Blow or brush the dust off the supply board and out of the case.
- If the board under the diodes has darkened, replace the four diodes. Forum members fitted larger diodes than the originals.[3]
- Check the solder joints of the +5 V regulator IC1050 while the board is out.[3]
The board has wire links marked J220V and J240V.[2] The NMS 8255 in the thread was set for 220 V. Check which link is fitted before use, and set it to suit your mains.[3]
Rail checks with two drives
[edit | edit source]| Rail | Regulator | Measured load on an NMS 8255 |
|---|---|---|
| +5 V | IC1050 (SI-3052V) | About 1.50 A; 1.56 to 1.60 A with a drive working |
| +12 V | IC1051 (L7812-RA) | About 0.22 A; 0.3 A with a drive working |
| -12 V | IC1052 (AN79M12) | Not measured |
Measure at the supply's output connector PC (pin 1 +12 V, pin 2 +5 V, pin 3 ground, pin 4 -12 V) with everything connected.[2] A +5 V reading that is correct off load but rises once the main board, analogue unit and drives are connected points at the regulator; see Philips NMS 8255 Troubleshooting Guide.[3]
Disk drives
[edit | edit source]The NMS 8255 has two drives of the same type (Philips part 4822 693 91114).[1] Drive alignment uses Philips's FDD test cartridge and alignment disk; the procedure is described on Philips NMS 8250 General Maintenance. For general drive care see Floppy Drive Repair.
Repair-Bas publishes a preventive modification for this drive, which was also used in the NMS 8250 and NMS 8280 and in several Sony, Panasonic and Sanyo MSX machines. It is for drives that still work. A small white part of the eject mechanism is removed and a small cam on it is cut away with a knife, so that the mechanism grips more firmly and does not spring back while a disk is being removed; the aim is to stop the head catching on the disk's shutter.[5] Follow the photographs in Repair-Bas's document.
Clock battery
[edit | edit source]The real-time clock keeps its settings on a NiCd accumulator on the main board (Philips part 4822 138 10213).[6] An MSX Resource Center member who has removed these cells from NMS 8250 and NMS 8255 machines says they are sealed and not known to leak, though by now they have usually discharged; he still recommends cutting them out.[7] Look at the cell and the board round it; if it has leaked, see Battery Explosion, Capacitor or Corrosion Damage. Without a working cell the clock and the settings it holds are lost at switch-off.[7]
Front panel
[edit | edit source]The plastic front panel becomes brittle with age and breaks easily under pressure, particularly in shipping.[8][7] Pack the machine so that nothing presses on the front. The MSX Resource Center links a source of 3D-printed replacement panels.[8]
Related pages
[edit | edit source]- Philips NMS 8255
- Philips NMS 8255 Troubleshooting Guide
- Philips NMS 8255 Capacitor Replacement Guide
- Philips NMS 8250 General Maintenance, for the shared procedures
- Philips NMS 8250 Documentation
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 Philips, Service Manual, Home computer NMS8250/00/16/19, NMS8255/00/16/19, PDF page 38, mechanical parts list: one list for both models, with floppy drives U104 and U103 (4822 693 91114), analog unit U102, power supply U101 and main panel U100. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 2.0 2.1 2.2 2.3 2.4 Philips, Service Manual NMS8250/NMS8255, PDF page 20 (sheet CS 7 580): mains through L901, F1001 (250 V, 2 A) and SW901 to the transformer; +5 V from F1050 (6.3 A T), bridge D1050 to D1053 (DSB15C), C1050 22000 µF and IC1050 (SI-3052V) with C1051 1000 µF; +12 V from bridge D1054 to D1057 (DSF10C), F1051 (1 A T), C1052 4700 µF, IC1051 (L7812-RA) and C1053 220 µF; -12 V through R1050, C1054 470 µF and IC1052 (AN79M12). PDF page 32: board layout 41 674 B12, with J220V and J240V links and output connector PC (1 +12 V, 2 +5 V, 3 ground, 4 -12 V). Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Philips NMS-8255 power (?) supply question and modding, July and August 2010—link(accessed 2026-10-21) Wild_Penguin's NMS 8255: dust coating the rectifier diodes D1050 to D1053 and darkened board round them, cured by cleaning and new diodes; a soldered wire link set for 220 V; +5 V rising to 5.78 to 5.94 V on load; currents measured on a PC supply of about 1.50 A at +5 V (1.56 to 1.60 A with a drive working) and 0.22 A at +12 V (0.3 A with a drive working). RetroTechie, 8 August 2010: NMS 8250/55 power supplies are not safe to touch, some parts carry mains voltage.
- ↑ Philips, Service Manual NMS8250/NMS8255, PDF page 2: caution, cartridges are to be exchanged with the set switched off; the ICs are sensitive to electrostatic discharge, so work connected to the set's ground through a wrist strap. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ Repair-Bas, Modificatie dubbelzijdige diskdrive (preventive modification for the double-sided disk drive), 2 pages, in Dutch, created 15 October 2010. https://repairbas.file-hunter.com/docs/drives/Preventieve%20modificatie%20dubbelzijdige%20diskdrive.pdf (retrieved 2026-10-21). Lists the drive as used in the Philips NMS 8250, NMS 8255 and NMS 8280, Sony HB-F500, HB-T600, HB-F700, HB-F900, HB-D20W and HBD-30W, Panasonic FS-FD1 and Sanyo MPC-25; only for drives that work normally; tightening the eject mechanism stops it springing back while a disk is removed so the drive head does not catch on the disk shutter; remove the white part and cut away the small cam with a knife, as shown in the photographs.
- ↑ Philips, Service Manual NMS8250/NMS8255, PDF page 36: main printed board parts list, including IC162 RP5C01 and the Ni-Cd accumulator 4822 138 10213. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 7.0 7.1 7.2 NMS8280 recapping, October and November 2020—link(accessed 2026-10-21) meits, 10 October 2020: the battery has probably fallen below 1 V and is useless; it is sealed and not known to leak, and the cells he showed came from NMS 8250s and 8255s left off for about twenty years with no sign of leakage; cutting it out is still best; a CR2032 with a diode to prevent charging has been used as a replacement. Pac: check the internal battery for leakage. Grauw: the front panel plastic of the Philips desktop models is very brittle and breaks easily under pressure, especially in shipping.
- ↑ 8.0 8.1 Philips NMS 8255, MSX Resource Center wiki, 7 March 2026—link(accessed 2026-10-21) "The plastic front panel also gets very fragile with age. Special care must be taken when shipping that absolutely no stress is placed on the front panel." The page links a source of 3D-printed NMS 8250 front panels.