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Philips NMS 8245 General Maintenance

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Philips NMS 8245 main board
NMS 8245 main board. The blue cylinder at the bottom right is the NiCd backup battery BT1 (MSX Resource Center wiki)

The Philips NMS 8245 is a one-piece MSX2 computer from 1987 with its power supply and a belt-driven 3.5-inch disk drive inside the case.[1][2] The two jobs that matter most on a machine of this age are removing or replacing the NiCd backup battery on the main board before it leaks, and replacing the drive belt.

Safety

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Mains voltage is present at the AC inlet, the mains switch and the primary of the transformer whenever the lead is plugged in. The power supply board itself works from the transformer's secondary windings.[3] Unplug the machine before opening it. Philips's manual also warns that cartridges must be changed with the computer switched off and that the ICs are sensitive to static: work on an earthed wrist strap.[4]

Inside the case

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Philips gives no written dismantling procedure, but the exploded views show how the machine is built. The top case carries the reset knob and the LED panel, with the keyboard underneath it on a cable. The bottom case holds the power supply board with the mains switch, the transformer, the main board, the encoder unit and the disk drive on its bracket, and the case screws go in from underneath.[5]

  1. Unplug the mains lead, any cartridges and all cables.
  2. Turn the machine over on a soft surface and remove the screws from the bottom case.
  3. Turn the machine back over and lift the top case a little. The keyboard and the LED panel are on cables.
  4. Note where the keyboard and LED panel cables go, unplug them, and lift the top case clear.

Backup battery

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The real-time clock (RP5C01, U13) keeps its settings on BT1, a NiCd accumulator (Philips part 4822 138 10235) on the main board.[6] It is the blue cylinder at the bottom right of the board. The MSX Resource Center gives it as a GB150H-2, 2.4 V, 150 mA, with 17 mm between its pins, and says it is prone to leaking; forum members say the 8245's batteries seem more likely to leak than those of the VG-8235, and that the blue sleeve holds two coin cells.[1][7]

  1. Open the case and find BT1 at the bottom right of the main board.
  2. Look at the board under and around it for green or white deposits and darkened tracks. If there are any, the cell has already leaked; see Battery Explosion, Capacitor or Corrosion Damage.
  3. Desolder BT1. Without it the computer still works, but the clock and the settings held in the RTC (screen width, colours, date) are lost at switch-off.[7]
  4. To keep the clock, fit a rechargeable cell of the same voltage. Forum advice is to mount it on wires away from the board and insulate it, so that a future leak cannot reach the board.[7]
  5. After fitting a new cell, set the clock and check that it keeps time. The RTC crystal is trimmed with TC1 to 32.768 kHz at pin 17 of U13.[4]

Disk drive

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The drive's spindle is driven by a belt.[2] A broken belt is a known cause of a drive that rattles briefly at switch-on and then reports "Disk offline"; one owner who opened a machine with that symptom also found the drive connector not pushed fully home.[8]

  1. Remove the drive with its bracket.
  2. Fit a new belt. Philips's part number is 4822 358 20269.[2]
  3. Check the drive's connector and seat it fully when refitting.
  4. Check the spindle speed: the index pulse at pin 1 of J1 should repeat every 200 ±0.5 ms, set at the adjustment point on the spindle motor.[2]

For head cleaning and general drive care see Floppy Drive Repair.

Power supply checks

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With the case open and the machine running, measure the rails against ground at a cartridge slot or at CN12 on the main board.[3] Philips's manual gives no tolerance for the rails.

NMS 8245 supply rails
Rail Regulator Fuse Slot pins
+5 V U1, STR2005 F1, T 3.15 A 45 and 47
+12 V U2, 7812 F1, T 3.15 A 48
−12 V U3, 7812 in a floating circuit F2, T 315 mA 50
Ground 41 and 43

[3][9]

The supply's electrolytic capacitors are listed in the Philips NMS 8245 Capacitor Replacement Guide. Forum advice on Philips MSX machines is to renew the main supply's capacitors whatever their condition and to leave the rest unless there is a reason.[10]

Adjustments

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Philips lists five adjustments on the main board and the encoder unit. Make them only after the supply is known to be good, and only if the symptom points to one of them.

NMS 8245 adjustments (service manual)
Circuit Measure at Adjust Target
VDP clock Pin 8 of U15 TC2 3,554,685 ±200 Hz
FDC read-pulse width Pin 29 of U8, with pin 22 of U8 linked to ground VR1 400 ±100 ns
FDC VCO Pin 16 of U8, with pin 22 of U8 linked to ground VR2 255 ±5 kHz
RTC clock Pin 17 of U13 TC1 (main board) 32.768 kHz
Encoder subcarrier Pin 17 of U1 on the encoder unit TC1 (encoder unit) 4,433,619 ±20 Hz

[4] Remove the link from pin 22 of U8 to ground after each FDC adjustment.[4] The drive alignment needs Philips's alignment disk (4822 395 30274) and FDD test cartridge (4822 397 30171).[2]

Cleaning

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  1. Blow dust out of the case, the power supply board and the drive with dry, low-pressure air.
  2. Clean the cartridge slot contacts with isopropyl alcohol on a lint-free swab and let them dry before use.
  3. Check the board for corrosion near BT1 every time the case is open.
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References

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  1. ↑ 1.0 1.1 Philips NMS 8245, MSX Resource Center wiki, 11 August 2026—link(accessed 2026-10-21) Released September 1987; built-in double-sided drive; internal GB150H-2 NiCd battery for the RTC, 2.4 V, 150 mA, 17 mm pin spacing, described as prone to leaking and to be removed.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Philips, Service Manual, Home computer NMS8245/00/16, CS 11 823, 4822 727 16027, PDF pages 2, 3 and 5: floppy disk drive alignment and the FDD parts list (spindle motor 4822 535 92418, holder assembly 4822 404 60409, front 4822 432 10645, belt 4822 358 20269, complete PCB 4822 212 22884, bracket 4822 404 60411, stator and rotor of the stepper motor 4822 362 10265 and 4822 362 20234). Spindle speed: oscilloscope on J1 pin 1 (index) with the probe earth on TP3; adjust the index period to 200 ±0.5 ms with a screwdriver at alignment point A of the spindle motor (figure 7). Hosted as File:Philips NMS 8245 Service Manual.pdf.
  3. ↑ 3.0 3.1 3.2 Philips, Service Manual NMS8245/00/16, PDF page 13 (sheet CS 11 836): power supply circuit. 220 V mains through U106, L100 and the switch SW1 in U107 to the transformer T1; on board U101, winding CN1-1/CN1-2 through F1 (T 3.15 A) to bridge D1 to D4 (S2V10), reservoir C5, STR2005 regulator U1 with L1, L2 and C6 for +5 V, and 7812 regulator U2 with C10 and C7 for +12 V; winding CN1-3/CN1-4 through F2 (T 315 mA) to bridge D5 to D8 (MPG06G), C8, and 7812 U3 with C9 for −12 V. Outputs: AC4 to the drive (+5 V, ground, ground, +12 V) and AC5 to CN12 on the main board (+5 V, ground, ground, +12 V, −12 V), with C57 (220 µF), C58 (220 µF) and C59 (47 µF) on the main board side. Cartridge slot pins: +5 V on 45 and 47, +12 V on 48, −12 V on 50, ground on 41 and 43. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  4. ↑ 4.0 4.1 4.2 4.3 Philips, Service Manual NMS8245/00/16, PDF page 2 (CS 11 824): caution notes (change cartridges with the set switched off; ESD precautions with a wrist strap) and adjustments. VDP clock: frequency counter on 8-U15 through a 10:1 probe, adjust TC2 for 3,554,685 ±200 Hz. FDC read-pulse width: oscilloscope on 29-U8, connect 22-U8 to ground, adjust VR1 for 400 ±100 ns, then remove the link. FDC VCO frequency: counter on 16-U8, 22-U8 to ground, adjust VR2 for 255 ±5 kHz, then remove the link. RTC clock: counter on 17-U13, adjust TC1 for 32.768 kHz. Encoder unit: counter on 17-U1, adjust TC1 for 4,433,619 ±20 Hz. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  5. ↑ Philips, Service Manual NMS8245/00/16, PDF pages 24 and 25: exploded views (CS 11 842 and 42 786 D12); PDF page 26: mechanical parts list (1 reset knob, 2 LED panel, 3 cabinet top case, 4 keyboard /00 or /16, 6 power supply, 7 mains switch, 8 cabinet bottom case, 9 encoder unit, 11 PCB support, 12 SCART connector, 13 slot guide, 14 transformer, 16 and 22 50-way connectors, 17 AC inlet, 18 floppy drive, 19 printer connector, 21 recorder connector, 23 main panel /00/16, 24 joystick connector). Hosted as File:Philips NMS 8245 Service Manual.pdf.
  6. ↑ Philips, Service Manual NMS8245/00/16, PDF page 22: main printed board parts list (U13 RP5C01; BT1 Ni-Cd accumulator 4822 138 10235; X2 32.768 kHz; tantalum capacitors C6, C9, C10, C13, C49, C52, C53 and C56, 22 µF 16 V). Hosted as File:Philips NMS 8245 Service Manual.pdf.
  7. ↑ 7.0 7.1 7.2 Any danger for Philips VG-8235 / NMS-8245 mainboards?, July 2017—link(accessed 2026-10-21) Replies of 26 to 31 July 2017 by meits ("In the 8245 you should remove the battery"), Louthrax (the 8245's battery is the big blue cylinder at the bottom right; removing it loses the RTC settings such as screen width, colours and date; it can be replaced with an equivalent battery or two batteries; the 8245's batteries look more likely to leak than the VG-8235's) and hardwaremaker (two coin cells inside the blue cylinder, which has to be desoldered; a battery fitted on wires away from the board and insulated with heat-shrink is safer).
  8. ↑ Broken drive on Philips NMS8245, March 2021—link(accessed 2026-10-21) Micha, 25 and 26 March 2021: the 8245's drive gave a short rattle at boot and "Disk offline" on FILES; when opened, the belt was broken and the drive connector was not plugged in properly. Another member, ray2day, suspected the belt and pointed to Bas Ditta's parts site.
  9. ↑ Philips, Service Manual NMS8245/00/16, PDF page 23: power supply parts (U1 STR2005, U2 µPC7812HF, U3 MC7812CT, D1 to D4 S2V-10, D5 to D8 MPG06G). Hosted as File:Philips NMS 8245 Service Manual.pdf.
  10. ↑ Recap recommendations, June 2018—link(accessed 2026-10-21) Thread started by an NMS 8250 owner, 23 June 2018. RetroTechie: supply-bypass electrolytics round the board can often be removed without the machine stopping; audio and video capacitors show their condition in the output; the main power supply's capacitors are worth replacing regardless of condition; use the service manual's parts list against the board and the schematic for each capacitor's function; replace one at a time. Wlcracks: use Rubycon, Chemi-Con, Nichicon or Panasonic parts.



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