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Philips NMS 8245 Troubleshooting Guide

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Philips NMS 8245 power supply circuit (service manual)
NMS 8245 power supply U101, from sheet CS 11 836 of the service manual

Philips's service manual for the Philips NMS 8245 has adjustments, drive alignment, circuit diagrams and parts lists, but no fault-finding chart. The MSX Archive's collection of service manuals has no Philips repair method for the NMS 8245, though it holds one for the NMS 8250 and NMS 8255.[1][2] The NMS 8250's repair method is for a different main board and its IC numbers do not apply here.

First checks

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  1. Remove any cartridges and disconnect everything except the monitor or television.
  2. Switch on and watch the lamps on the panel above the keyboard: power, caps and FDD busy.[3][4]
  3. Open the case and measure the three rails at a cartridge slot, using pins 41 or 43 as ground: +5 V on pins 45 and 47, +12 V on pin 48, −12 V on pin 50.[5] Philips gives no tolerance for these rails.
  4. Look at the main board around BT1, the blue cylinder at the bottom right, for leaked electrolyte. A leak there can damage tracks nearby.[6]

Power faults

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NMS 8245 power faults
Symptom Probable cause Action
No lamps, nothing happens Mains switch, transformer, or F1 on the supply board Check the mains lead and switch. Unplug, then check F1 (T 3.15 A) and the transformer windings for continuity.
+5 V and +12 V missing, −12 V present F1, bridge D1 to D4, reservoir C5 Measure across C5. No voltage there with F1 good points to the bridge or the transformer winding.
Voltage across C5 present, +5 V missing or low U1 (STR2005), L1, L2, C6 Check U1's output and the coils. Disconnect AC5 to see whether the main board is pulling the rail down.
+12 V missing, +5 V present U2 (7812), C10, C7 Measure the input and output of U2.
−12 V missing F2 (T 315 mA), bridge D5 to D8, C8, U3 Check F2 first, then the bridge and U3.
Drive dead, computer works AC4 connector or the drive's own supply Check +5 V and +12 V at AC4.

[5]

Display faults

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NMS 8245 display faults
Symptom Probable cause Action
Power lamp on, no picture on any output Supply, CPU or video processor not running Check all three rails first. Then check the VDP clock at pin 8 of U15 (V9938): 3,554,685 Hz ±200 Hz, trimmed with TC2.
No colour, or unstable colour, on the composite or RF output Encoder unit (MC1377) or its crystal Measure the subcarrier at pin 17 of U1 on the encoder unit: 4,433,619 ±20 Hz, adjusted with TC1 on the encoder unit.
No picture on RF only Modulator on the encoder unit, or tuning The RF output is on UHF channel E36. Tune the television to it before suspecting the modulator.

[7][3]

Disk drive faults

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NMS 8245 disk drive faults
Symptom Probable cause Action
Short rattle at switch-on, then "Disk offline" Broken drive belt; drive connector not seated Open the case, fit a new belt (Philips 4822 358 20269) and reseat the drive connector.
Drive spins but reads unreliably Spindle speed, FDC data separator, or head alignment Check the index period at pin 1 of J1: 200 ±0.5 ms. Then check the FDC read-pulse width (pin 29 of U8, 400 ±100 ns) and VCO (pin 16 of U8, 255 ±5 kHz).
Reads its own disks, not disks from other machines Head alignment Philips's alignment uses the alignment disk 4822 395 30274 and the FDD test cartridge 4822 397 30171 (CALL FDDTEST): radial alignment, track 00 sensor, azimuth within ±30′ and index burst 400 ±200 µs.

[8][9][7] General drive care is in Floppy Drive Repair.

Clock and settings

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NMS 8245 clock faults
Symptom Probable cause Action
Date, screen width and colours lost at every switch-off BT1 flat, removed or leaking Inspect BT1 and the board round it. Replace or remove it as described in the Philips NMS 8245 General Maintenance guide.
Clock keeps running but gains or loses time RTC crystal trim Set the frequency at pin 17 of U13 to 32.768 kHz with TC1.

[6][7]

Other faults

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  • No picture, sound or drive activity with a cartridge in either slot, but normal without it: the cartridge or the slot contacts. Philips's manual says cartridges must be changed with the power off.[7]
  • No sound: the sound generator is inside the S-3527 (U11) MSX controller. Check the cable and the output in use before suspecting the board.[10][11]
  • Electrolytic capacitors in the supply age like any others; the values are in the Philips NMS 8245 Capacitor Replacement Guide. General signs of failing capacitors are on Capacitor Failure Symptoms.
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References

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  1. ↑ Philips, Service Manual, Home computer NMS8245/00/16, CS 11 823, order code 4822 727 16027: 28 pages of specification, adjustments, drive alignment, diagrams, layouts and parts lists. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  2. ↑ Index of /pub/msx/docs/service_manuals, MSX Archive—link(accessed 2026-10-21) Directory listing: philipsnms8245sm.pdf (NMS 8245 service manual), philipsnms8250rm.pdf (NMS 8250 repair method), and repair methods for the VG-8235; no repair method for the NMS 8245.
  3. ↑ 3.0 3.1 Philips, Service Manual NMS8245/00/16, PDF page 23: LED panel U103 (LD1 yellow, LD2 and LD3 green, SW1 reset switch); power supply U101 (U1 STR2005, U2 µPC7812HF, U3 MC7812CT, D1 to D4 S2V-10, D5 to D8 MPG06G); encoder unit U102 (IC1 MC1377, X1 4.433619 MHz, DL1 400 ns delay line, modulator, CN2 monitor connector); floppy disk drive U104 4822 212 22883. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  4. ↑ File:Philips NMS 8245 top view.jpg, photograph from the MSX Resource Center wiki: the lamps above the keyboard are labelled POWER, CAPS and FDD BUSY.
  5. ↑ 5.0 5.1 Philips, Service Manual NMS8245/00/16, PDF page 13 (sheet CS 11 836): power supply U101 circuit (F1 T 3.15 A, bridge D1 to D4, C5 3300 µF, U1 STR2005 with L1, L2, R1 3.3 kΩ and C6 1000 µF for +5 V; U2 7812 with C10 10 µF and C7 220 µF for +12 V; F2 T 315 mA, bridge D5 to D8, C8 220 µF, U3 7812 and C9 10 µF for −12 V); output AC4 to the floppy drive (+5 V and +12 V) and AC5 to CN12 on the main board (+5 V, +12 V, −12 V); cartridge slot pins +5 V 45 and 47, +12 V 48, −12 V 50, ground 41 and 43. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  6. ↑ 6.0 6.1 Any danger for Philips VG-8235 / NMS-8245 mainboards?, July 2017—link(accessed 2026-10-21) Louthrax, 27 July 2017: if the batteries start leaking "that can really damage the board"; the 8245's battery is the big blue cylinder at the bottom right and seems more likely to leak than the VG-8235's.
  7. ↑ 7.0 7.1 7.2 7.3 Philips, Service Manual NMS8245/00/16, PDF page 2 (CS 11 824): adjustments. VDP clock: counter on 8-U15, TC2 for 3,554,685 ±200 Hz. FDC read-pulse width at 29-U8 with 22-U8 grounded, VR1, 400 ±100 ns. FDC VCO at 16-U8 with 22-U8 grounded, VR2, 255 ±5 kHz. RTC clock at 17-U13, TC1, 32.768 kHz. Encoder unit: counter on 17-U1, TC1 for 4,433,619 ±20 Hz. Page 1: RF output on UHF channel E36. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  8. ↑ Broken drive on Philips NMS8245, March 2021—link(accessed 2026-10-21) Micha, March 2021: a short rattling sound at boot and "Disk offline" on FILES; the belt was broken and the drive connector was not plugged in properly.
  9. ↑ Philips, Service Manual NMS8245/00/16, PDF pages 2 and 3: floppy disk drive alignment with a dual-trace oscilloscope, alignment disk 4822 395 30274 and FDD test cartridge 4822 397 30171 (CALL FDDTEST); radial alignment by the cat's-eye pattern on track 40; track 00 sensor (62.5 kHz pattern on track 00 only, or 3.5 V, 1.5 V and 0.5 V across the sensor on tracks 00, 01 and 02); azimuth ±30′, not adjustable; index burst 400 ±200 µs; spindle speed by the index period of 200 ±0.5 ms. PDF page 5: FDD parts list including the belt 4822 358 20269. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  10. ↑ Philips NMS 8245, MSX Resource Center wiki, 11 August 2026—link(accessed 2026-10-21) PSG integrated in the Yamaha S3527 MSX-Engine; connections are the RF output, an 8-pin CVBS monitor connector, SCART RGB, data recorder, Centronics printer port, two general-purpose ports and two cartridge slots.
  11. ↑ Philips, Service Manual NMS8245/00/16, PDF page 22: main printed board parts list (U11 S-3527, U13 RP5C01, U15 V9938, U8 2793, BT1 Ni-Cd accumulator). Hosted as File:Philips NMS 8245 Service Manual.pdf.



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