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Philips NMS 8245 Capacitor Replacement Guide

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Philips NMS 8245 power supply board layout (service manual)
NMS 8245 power supply board (42 719 B12) and LED panel, from the service manual. The polarised capacitors C5 to C10 are marked with a plus sign

The Philips NMS 8245 has a separate power supply board, U101, with six electrolytic capacitors. Their values and voltage ratings are printed on the power supply circuit diagram in Philips's service manual, and three more on the main board side of the supply connector.[1][2] The parts list names the main board's tantalum capacitors but not its small electrolytics, so those have to be read from the board.[3]

Power supply capacitors

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Philips prints each electrolytic's voltage as a code letter on the diagram; the table gives it in volts.[2]

NMS 8245 power supply board (U101) electrolytics
Ref Value Voltage Position in the circuit
C5 3300 µF 25 V Reservoir after bridge D1 to D4, input of U1 (STR2005) and U2
C6 1000 µF 6.3 V +5 V output of U1, after L1 and L2
C10 10 µF 25 V Input of U2 (7812, +12 V)
C7 220 µF 16 V +12 V output of U2
C8 220 µF 25 V Reservoir after bridge D5 to D8, input of U3
C9 10 µF 16 V −12 V output of U3

[1][2]

NMS 8245 main board supply capacitors at CN12
Ref Value Voltage Rail
C57 220 µF 16 V +5 V
C58 220 µF 16 V +12 V
C59 47 µF 16 V −12 V

[1]

C6 is a 6.3 V part on a 5 V rail. Fit a replacement of at least the original voltage; a 10 V part of the same capacitance gives more margin if it fits the space. Check the polarity of C9 and C59 against the board: they sit on the −12 V rail.[1]

Tantalum capacitors

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The main board has eight 22 µF 16 V tantalum capacitors: C6, C9, C10, C13, C49, C52, C53 and C56.[3] They share designators with the supply board's capacitors (both boards have a C6, C9 and C10), so always say which board a part is on.

Other electrolytics

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The main board and the encoder unit carry further small electrolytics that the parts lists do not itemise. The main board's are on the circuit diagrams (PDF pages 13 to 18 of the manual), and the photograph of an NMS 8245 main board shows several on the encoder board at the top left.[4] Record them before ordering:

  1. Photograph each board from above, then each electrolytic close up so the printing can be read.
  2. Write down the designator, capacitance, voltage, diameter and height, and which side the stripe faces.
  3. Check each against the circuit diagram in the manual. Where the board and the diagram differ, go by the board.
Template for the main board and encoder unit
Board Ref Value Voltage Diameter × height Notes

Forum advice on Philips MSX machines is to replace the main supply's capacitors whatever their condition, to judge the audio and video capacitors by the picture and sound, and to leave the bypass capacitors round the board unless there is a reason.[5]

Procedure

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  1. Unplug the machine and open the case as described in the Philips NMS 8245 General Maintenance guide.
  2. Remove BT1 from the main board first if it is still fitted; see the same guide.
  3. Unplug the supply board's connectors (AC4 to the drive, AC5 to the main board, and the transformer leads at CN1), noting their positions, and lift the board out.[1]
  4. Replace one capacitor at a time, matching the polarity marks on the board layout.[5][6]
  5. Refit the board and its connectors.

After the recap

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Switch on and measure the rails at a cartridge slot against pin 41 or 43: +5 V on pins 45 and 47, +12 V on pin 48, −12 V on pin 50.[1] Then check that MSX-BASIC starts, that the drive reads a disk, and that the picture is stable. Remaining faults are covered in the Philips NMS 8245 Troubleshooting Guide.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Philips, Service Manual, Home computer NMS8245/00/16, CS 11 823, order code 4822 727 16027, PDF page 13 (sheet CS 11 836): power supply U101 circuit diagram and the main board end of connector CN12. Values with their voltage code letters: C5 3300 µF f, C6 1000 µF c, C10 10 µF f, C7 220 µF e, C8 220 µF f, C9 10 µF e; C1 to C4 10 nF across the rectifiers; on the main board, C57 220 µF e (+5 V), C58 220 µF e (+12 V), C59 47 µF e (−12 V). Hosted as File:Philips NMS 8245 Service Manual.pdf; the supply part is reproduced as File:Philips NMS 8245 power supply circuit (service manual).png.
  2. ↑ 2.0 2.1 2.2 Philips, Service Manual NMS8245/00/16, PDF page 28: "Symbols used in circuit diagrams" (39 301 A13). Electrolytic capacitors are ±20 %, with the voltage given by a letter: a 2.5 V, b 4 V, c 6.3 V, d 10 V, e 16 V, f 25 V, g 40 V, h 63 V. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  3. ↑ 3.0 3.1 Philips, Service Manual NMS8245/00/16, PDF page 22: main printed board parts list. Capacitors listed: C6, C9, C10 and C13, tantalum 22 µF 16 V (4822 124 10527); C15 mylar 220 nF 50 V; C19 mylar 10 nF 50 V; C35 and C39 mylar 22 nF 50 V; C37 and C64 mylar 3.3 nF 50 V; C49, C52, C53 and C56, tantalum 22 µF 16 V (4822 124 10527); TC1 and TC2 30 pF trimmers. Page 23: encoder unit C10 1 nF 50 V film, TC1 30 pF trimmer. Hosted as File:Philips NMS 8245 Service Manual.pdf.
  4. ↑ File:Philips NMS 8245 main board.jpg, photograph of an NMS 8245 main board uploaded to the MSX Resource Center wiki by Mars2000you, 10 March 2016: radial electrolytics on the encoder and modulator board at the top left and a few on the main board.
  5. ↑ 5.0 5.1 Recap recommendations, June 2018—link(accessed 2026-10-21) RetroTechie, 23 June 2018: bypass electrolytics round an MSX board can often be removed without the machine stopping; audio and video capacitors show their condition in the output; replace the main power supply's capacitors regardless of condition; compare the service manual's parts list with the board; replace capacitors one at a time. Wlcracks: use Rubycon, Chemi-Con, Nichicon or Panasonic parts.
  6. ↑ Philips, Service Manual NMS8245/00/16, PDF page 20: power supply board layout 42 719 B12 and LED panel 42 717 A12, with the polarity of C5 to C10 marked. Reproduced as File:Philips NMS 8245 power supply board layout (service manual).png.



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