Philips NMS 8255 Capacitor Replacement Guide
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The Philips NMS 8255 has the same power supply, main board and analogue unit as the Philips NMS 8250, drawn in one Philips service manual. The supply's electrolytics and the three at the main board's supply input are printed on the circuit diagram with their voltage codes, and they are tabulated with their circuit positions on Philips NMS 8250 Capacitor Replacement Guide.[1][2] The sections below add NMS 8255 owners' experience and the audio capacitors involved in the known sound faults.
Supply capacitors, briefly
[edit | edit source]| Ref | Value | Voltage | Rail |
|---|---|---|---|
| C1050 | 22000 µF | 16 V | +5 V reservoir |
| C1051 | 1000 µF | 10 V | +5 V output |
| C1052 | 4700 µF | 25 V | +12 V reservoir |
| C1053 | 220 µF | 16 V | +12 V output |
| C1054 | 470 µF | 25 V | -12 V, after R1050 |
| C102 | 47 µF | 10 V | +5 V at the main board |
| C103 | 47 µF | 16 V | +12 V at the main board |
| C101 | 22 µF | 16 V | -12 V at the main board |
On Wild_Penguin's NMS 8255, whose +5 V rail rose to almost 6 V on load, C1051 was replaced with a 1000 µF 10 V part. It did not cure the fault, which pointed to the regulator IC1050; replace C1051 anyway when recapping, but check the regulator if the rail is high.[3] The large reservoir C1050 sits beside the rectifiers D1050 to D1053, which run hot; clean away any dust and look at the board round them when the capacitor is out.[3][1]
Audio capacitors on the main board
[edit | edit source]| Ref | Value | Voltage | Position |
|---|---|---|---|
| C119 | 100 µF | 10 V | PPI beep (PPISND) into the audio mix, after R169 |
| C121 | 100 µF | 10 V | PSG output of Q102 into the mix, after R170 |
| C122 | 470 µF | 10 V | Decoupling of the Q102 collector supply (R171, R172) |
Fit C119 by the circuit, not the board print. The article translated by Hans Otten says the print for C119 is reversed and the capacitor is often found fitted the wrong way round.[5] Note the orientation of the existing part before removing it, then compare it with the circuit diagram: on Wild_Penguin's machine it was already correct.[3]
Analogue unit
[edit | edit source]The article also replaces the two 100 Ω resistors R428 and R429 on the NMS 8250/8255 analogue board with 100 µF 10 V electrolytics, negative lead towards connector AB.[5] This adds two capacitors that a standard board does not have. Wild_Penguin made the change on his NMS 8255 and heard no difference, so treat it as optional.[3]
The analogue unit's other electrolytics are drawn on PDF page 16 of the service manual, but the scan's shading makes many values hard to read; record them from the board.[6]
| Board | Ref | Value | Voltage | Diameter × height | Stripe side |
|---|---|---|---|---|---|
Procedure
[edit | edit source]- Unplug the machine and open it as described on Philips NMS 8250 General Maintenance. The supply carries mains voltage.
- Start with the supply board: C1050 to C1054. While it is out, clean the dust from the rectifiers and inspect the board under them.[3]
- Replace the main board's supply-input capacitors C101 to C103, then the audio capacitors C119, C121 and C122, checking C119's polarity against the diagram.[1][4]
- Replace one capacitor at a time.[7]
- Before reconnecting the main board, measure the supply outputs off load, then on load. +5 V must stay within about 5.0 ±0.25 V with everything connected, including both drives.[3]
Other faults are on Philips NMS 8255 Troubleshooting Guide.
Related pages
[edit | edit source]- Philips NMS 8255
- Philips NMS 8255 General Maintenance
- Philips NMS 8255 Troubleshooting Guide
- Philips NMS 8250 Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 Philips, Service Manual, Home computer NMS8250/00/16/19, NMS8255/00/16/19, PDF page 20 (sheet CS 7 580), power supply U101: C1050 22000 µF (code e), C1051 1000 µF (d), C1052 4700 µF (f), C1053 220 µF (e), C1054 470 µF (f, faint in the scan); main board end: C102 47 µF (d) on +5 V, C103 47 µF (e) on +12 V, C101 22 µF (e) on -12 V. PDF page 32: board layout 41 674 B12. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 2.0 2.1 2.2 Philips, Service Manual NMS8250/NMS8255, PDF page 40: symbols used in circuit diagrams, with the capacitor voltage code (c 6.3 V, d 10 V, e 16 V, f 25 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 Philips NMS-8255 power (?) supply question and modding, July and August 2010—link(accessed 2026-10-21) Wild_Penguin's NMS 8255: +5 V at 5.78 to 5.94 V on load; RetroTechie suggested replacing C1051 (1000 µF) first as cheap and easy, then the regulator; Wild_Penguin replaced C1051 with 1000 µF 10 V on 10 August 2010 without change; RetroTechie then put it down to the +5 V regulator. The rectifier diodes D1050 to D1053, beside the large reservoir, had been coated in dust over a darkened board. C119 on his board was already fitted the right way, opposite to the print; he converted R428 and R429 to electrolytics.
- ↑ 4.0 4.1 Philips, Service Manual NMS8250/NMS8255, PDF page 22: sound circuit of IC101 (S-3527) with Q102 (2SC536NP); C119 100 µF (d) after R169 12 kΩ on PPISND; C121 100 µF (d) after R170 1 kΩ on the collector of Q102; C122 470 µF (d) between R172 and R171; C120 1 nF; output AUDIO on connector MB. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 5.0 5.1 Verminkt geluid bij NMS 8250/55/80 (Distorted sound for NMS8250/55/80), from Digital KC, scanned and translated with comments by Hans Otten (2001 and 2002), 4 pages. https://download.file-hunter.com/Technical/Hans%20Otten/nms82xxgeluid.pdf (retrieved 2026-10-21). C119 on the main board is an electrolytic whose board print is reversed and which is often fitted the wrong way round: turn it. On the 8250/55 analogue board, R428 and R429 (100 Ω) should be 100 µF 10 V electrolytics with the negative lead towards connector AB.
- ↑ Philips, Service Manual NMS8250/NMS8255, PDF page 16: analog unit U102 circuit diagram with its component index; the shaded background makes small values hard to read in the scan. Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ Recap recommendations, June 2018—link(accessed 2026-10-21) Thread about recapping a Philips NMS 8250. RetroTechie: replace the main power supply's capacitors regardless of condition; judge audio and video capacitors by the output; replace one capacitor at a time; Rubycon, Chemi-Con, Nichicon or Panasonic from established distributors.