Philips NMS 8250 Troubleshooting Guide
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Philips wrote a fault-finding guide for the Philips NMS 8250 and NMS 8255: the Repair Method (order code 4822 727 15847). It works from what the machine shows at switch-on with Philips's service test cartridge fitted, then from the error numbers the cartridge's tests report, and names the IC pins to check for each.[1] Without the cartridge (4822 397 30138), the screen colours, error descriptions and check points still show which part of the board each test covers. Community reports on the power supply and the video board are added where they apply.
First checks
[edit | edit source]- Remove any cartridges, connect a television or monitor and switch on. The power LED should light; if it does not, check the power supply and the LED.[2]
- Open the case and measure the rails at the supply connector or a cartridge slot: +5 V, +12 V and −12 V.[3] Daemos on the MSX Resource Center forum puts it first: "check voltages first".[4]
- Check that SW101, the service switch on the main board, is in its normal position.[5][4]
Power supply faults
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Power LED off, nothing happens | Mains switch SW901, fuse F1001, transformer T901 | Check the mains lead and switch. Unplug, then check F1001 (2 A) and the transformer windings. |
| +5 V missing | F1050 (6.3 A), bridge D1050 to D1053, C1050, IC1050 | Check F1050. Measure across C1050. If it is present there, check IC1050 (SI-3052V). |
| Picture and sound level rise slowly, then drop; occasional hang | Overheated rectifiers D1050 to D1053 | Look for dust on the diodes and a darkened board under them. Replace the four diodes and clean the supply. |
| +5 V correct off load, high (about 5.8 V) with the board connected | IC1050 or its solder joints | Reflow the regulator's joints. If the fault remains, replace the regulator. Do not run the machine on the high rail. |
| +12 V missing | F1051 (1 A), bridge D1054 to D1057, C1052, IC1051 | Check F1051 first, then the bridge and IC1051. |
| −12 V missing | R1050, C1054, IC1052 (AN79M12) | R1050 carries a safety warning triangle on the diagram, and Philips requires identical parts in such positions: replace it only with the same part. |
Screen colour at switch-on (service cartridge)
[edit | edit source]With the service test cartridge fitted and SW101 set for service mode, the screen colour at switch-on shows how far the machine gets.[2]
| Screen | Meaning | Check |
|---|---|---|
| Black, no picture | CPU not running, or no video output | CPU IC145: clock, supply, data, address and control bus before and after the buffers IC130, IC132, IC144, IC166 and IC156. Video at 6-IC143, IC106 pins 22, 23, 24, 30 and 31, IC301, IC148, Q316, the RF modulator A301 and the SCART connector. |
| Blue | Start-up tests passed or failed | An error number, or the memory map. Press RETURN and choose the test closest to the complaint. |
| Green, then dark blue | Video data line error, D0 to D3 | IC103, IC105 (pins 2, 3, 15, 17) and IC106 (pins 41 to 44) |
| Green, then pale blue | Video data line error, D4 to D7 | IC102, IC104 (pins 2, 3, 15, 17) and IC106 (pins 45 to 48) |
| Green, then red | Video address bus error | IC106 pins 49 to 56; IC102 to IC105 pins 6 to 8 and 10 to 14 |
| Green, then yellow | Video RAS, CAS or R/W error | IC106 pins 30, 31, 57, 60, 61, 62; IC102 to IC105 pins 4, 5, 16 |
On one NMS 8250 with a black screen and a drive that kept seeking, Repair-Bas found the PAL encoder on the video board broken.[4]
Error numbers
[edit | edit source]The service cartridge's tests report these numbers. The page numbers are the repair method's printed pages.[7]
| Error | Meaning | Where to look |
|---|---|---|
| ERR 001 | Several keys pressed at once, or characters appear without a key | IC101 column lines (pins 66 to 73) and row lines (pins 74 to 82) |
| ERR 002 | A key stays closed | Replace the keyboard |
| ERR 101 | Joystick direction wrong | Switch held closed in the joystick; IC101 pins 48 to 51 and 55 to 58 |
| ERR 102 | Two action switches on one joystick | Q104 and IC101 pins 52 and 53 (port 1); Q105 and IC101 pins 59 and 60 (port 2) |
| ERR 103 | The other joystick responds | IC101 pins 48 to 53 and 55 to 60 |
| ERR 211 | No RAM from C000 to FFFF | CAS, RAS and WE lines to IC133 to IC136; RSEL at pin 8 of IC115 |
| ERR 212 | Memory mapper fault | IC149 and its connections |
| ERR 215 | Address selection fault | ASEL at pin 8 of IC115; IC147, IC149, IC150 |
| ERR 221 | Open RAM data line | Bank 1: D0 to D3 on IC134, D4 to D7 on IC133. Bank 2: D0 to D3 on IC136, D4 to D7 on IC135 |
| ERR 241 | Slot selection fault | Pin 8 of IC115, pin 9 of IC101, A14 and A15 at IC101 |
| ERR 261 | Faulty RAM chip | The data bits reported; IC146, IC147, pin 44 of IC101 |
| ERR 271 | Open or shorted address line A0 to A7 | IC133, IC134, IC146, IC147 (bank 1); IC135, IC136 (bank 2) |
| ERR 281 | Refresh error, or open A8 to A15 | IC146, IC147, IC150, IC111; the RAM chips of the bank reported |
| ERR 301, 311, 312 | Cassette header or data not read | Signal path from pin 5 of MD to pin 1 of IC101 when reading, and from pin 2 of IC101 to pin 4 of MD when writing |
| ERR 400 | Sound generator registers | The S-3527, IC101 |
| ERR 711 | RTC RAM not available | IC162, IC159, IC127, IC175, IC172, IC171, IC161 |
| ERR 715 | RTC mode selection | Pin 10 of IC162 |
| ERR 721 | RTC data lines | IC162, pin 12 of IC159 |
| ERR 771 | RTC address lines | IC162, IC172, IC161 |
| ERR 799 | RTC time function | Pins 16 and 17 of IC162, crystal X102 |
| ERR 801 | Printer bit lines | IC101, the printer cable, the printer |
| ERR 810 | No communication with the printer | Printer connected; pins 91 and 100 of IC101 |
| ERR 990 | Interrupt length not 20 ±2 ms | IC145, IC110, IC125, pin 25 of IC106, IC156 |
| ERR 999 | No interrupt from the VDP | Pin 16 of IC145, IC110, IC125, pin 25 of IC106 |
The sum check test reports a checksum for each ROM. The repair method gives D41F for the test cartridge (version 090187); for the BASIC ROM 8223 (/00), BF2E (/16) and 6EF7 (/19); for the expansion ROM CF9D (/00), 0748 (/16) and CBFF (/19); and 293E for the disk ROM, or 2788 for the "fast version".[8]
Disk drive faults
[edit | edit source]The floppy interface has its own error numbers, reported by Philips's FDD test cartridge (service code 4822 397 30135). The same number can come from the drive or from the interface, so swap the drive first to see which.[9]
| Error | Meaning | Where to look |
|---|---|---|
| ERR 001 | Disk off line | IC153 pins 27 and 34, IC163, IC140, IC154, IC164, IC142, IC139, IC124, IC137, IC128 |
| ERR 101, 110, 111, 201, 210, 211 | Track 00 errors | Pin 34 of IC153, IC163, IC140; the drive's track 00 sensor |
| ERR 106, 206, 306 | Write protect errors | The disk's write-protect slide; IC153, IC163, IC140 |
| ERR 301 | Index error | Pin 35 of IC153, IC163, IC140 |
| ERR 305 | Write error | IC153, IC110, IC148, IC164 |
| ERR 307 | Disk not ready | Pin 32 of IC153, IC163, IC140 |
| ERR 308 | Wrong side | IC142, IC152, IC126 |
| ERR 401, 402 | Data request, lost data | Pin 38 of IC153, IC110, IC148, IC124 |
| Other ERR 3xx to 5xx | FDC errors | IC153 (WD2793A) |
[9][5] Drive alignment is in the service manual and needs the alignment disk 4822 395 30274.[10] See also Floppy Drive Repair.
Cartridge problems
[edit | edit source]If the machine misbehaves only with a cartridge fitted, the repair method points to the bus buffers IC165 to IC170.[9] Change cartridges only with the power off.[10] The MSX Resource Center describes poor mixing of SCC and other sound cartridges with the internal sound as a known trait of the model, with several modifications that cure it.[11]
Related pages
[edit | edit source]- Philips NMS 8250
- Philips NMS 8250 General Maintenance
- Philips NMS 8250 Capacitor Replacement Guide
- Philips NMS 8250 Documentation
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ Philips, Repair Method, Home computer NMS8250/00/16/19, NMS8255/00/16/19, order code 4822 727 15847, cover CS 7 946 and contents. Hosted as File:Philips NMS 8250 and NMS 8255 Repair Method.pdf.
- ↑ 2.0 2.1 2.2 Philips, Repair Method NMS8250/NMS8255, printed page 3, "Repair method NMS8250/NMS8255": remove external cartridges, connect a TV or monitor, switch on; power LED off: check the power supply and the power-on LED. Switch off, fit the service test cartridge 4822 397 30138, switch the computer into service mode with the test switch on the main unit, switch on, and note the screen colour. Black (no picture): check the CPU (IC145) primary conditions (clock, supply voltage, data, address and control bus before and after buffers IC130, IC132, IC144, IC166 and IC156) and the video signal at 6-IC143, 22-23-24-30-31-IC106, 9-3-4-5-IC301, 13-14 IC148, Q316, the RF modulator (A301) and the SCART connector. Blue: an error message, or the memory map, then select a test; with problems in the initial screen format or colours, the key click or the password an RTC test is recommended. Green, then dark blue: video data line error D0 to D3 (2-3-15-17-IC103 and IC105, 41 to 44-IC106; 5-IC156 MREQ, 13-IC180, 4-IC175, 5-IC170, 36-IC101). Pale blue: video data line error D4 to D7 (2-3-15-17-IC102 and IC104, 45 to 48-IC106). Red: video address bus error (49 to 56-IC106; 6 to 8 and 10 to 14 of IC102 to IC105). Yellow: video control bus error, RAS, CAS, R/W (30-31-57-61-62-IC106; 4-5-16 of IC102 to IC105; 60-IC106, 16-IC103, 16-IC105; 9-IC156, 7-39-IC101). Hosted as File:Philips NMS 8250 and NMS 8255 Repair Method.pdf.
- ↑ 3.0 3.1 Philips, Service Manual, Home computer NMS8250/00/16/19, NMS8255/00/16/19, PDF page 20 (sheet CS 7 580): power supply U101. +5 V from F1050 (6.3 A), bridge D1050 to D1053, C1050 22000 µF and IC1050 SI-3052V, with C1051 1000 µF; +12 V from bridge D1054 to D1057, F1051 (1 A), C1052 4700 µF and IC1051 7812, with C1053 220 µF; −12 V through R1050, C1054 470 µF and IC1052 AN79M12. Mains through L901, F1001 (2 A) and SW901 to T901; R1050 marked with a warning triangle. Cover page: "Safety regulations require that the set be restored to its original condition and that parts which are identical with those specified be used." Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ 4.0 4.1 4.2 NMS 8250 broken, February and March 2023—link(accessed 2026-10-21) rolandve, 20 February 2023: at switch-on the drive made noises, the screen stayed black and the cycle repeated; later the drives stayed dead. Daemos: check the voltages first; the power supplies "are notorious for long term failures"; "the diodes are your usual suspects"; check for ripple with a scope. larsthe18th: the white switch SW101 in the centre of the main board, left of the floppy connector, may have been pressed. Repair-Bas, 14 March 2023: "Pal encoder was broken"; rolandve: "a new video board".
- ↑ 5.0 5.1 Philips, Service Manual NMS8250/NMS8255, PDF page 36: main printed board parts list (SW101 service switch 4822 276 12227; IC101 S-3527; IC102 to IC105 and IC133 to IC136 81464-12; IC106 V9938; IC145 Z80A; IC153 WD2793A; IC162 RP5C01; X102 32.768 kHz). Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ Philips NMS-8255 power (?) supply question and modding, July and August 2010—link(accessed 2026-10-21) On an NMS 8255, which shares the NMS 8250's supply. Wild_Penguin, 16 and 17 July 2010: picture brightness and PSG level rose gradually and then dropped, with a pop and once a hang; the rectifier diodes D1050 to D1053 were coated in dust with the board darkened round them, and replacing them solved it. 10 August 2010: +5 V within 0.1 V off load but about 5.78 V with the main board connected, and about 7.4 V with the drives disconnected as well. RetroTechie: check the +5 V regulator's solder joints (a loose ground pin, for example); "has all the signs of a dodgy +5V regulator"; do not use the supply until it is fixed; the rectifier diodes "regularly fail".
- ↑ 7.0 7.1 Philips, Repair Method NMS8250/NMS8255, printed pages 4 to 20: keyboard test (TAB): ERR 001 several keys activated at once, ERR 002 a key held closed (replace the keyboard); joystick test (F1): ERR 101 incorrect direction, ERR 102 two actions on one joystick (Q104 for joystick 1, Q105 for joystick 2), ERR 103 another joystick activated; RAM test (F2): two banks of 64 KB, IC133 and IC134 bank 1, IC135 and IC136 bank 2; ERR 211 RAM not present from C000 to FFFF, ERR 212 incorrect memory mapper, ERR 215 incorrect address selection, ERR 221 open data lines (bank 1: D0 to D3 on IC134, D4 to D7 on IC133; bank 2: D0 to D3 on IC136, D4 to D7 on IC135), ERR 241 incorrect slot selection, ERR 261 incorrect RAM chip, ERR 271 incorrect address line (A0 to A7), ERR 281 refresh error or an open address line A8 to A15 on IC146 or IC147; cassette test (F3): ERR 301 header not read correctly, ERR 311 data cannot be read, ERR 312 data not read correctly; sound test (F4): ERR 400 sound generator registers in the S-3527 (IC101) defective; no sound at all: check 5-IC101, Q321 for SCART and Q322 for audio out and the RF modulator; I/O test (F5); pattern test (INS) with the video RAM test; sum check test (DEL); RTC test (CODE): ERR 711 RTC RAM not available, ERR 715 incorrect mode selection (10-IC162), ERR 721 incorrect data lines (IC162, 12-IC159), ERR 771 incorrect address lines (IC162, IC172, IC161), ERR 799 incorrect time function (16-17-IC162, X102); printer test (ESC): ERR 801 incorrect bit lines, ERR 810 no communication (100-IC101, 91-IC101); ERR 990 interrupt duration not 20 ±2 ms (16-IC145, 5-6-IC110, IC125, 25-IC106, 24-IC145, 41-IC101, IC156, 27-IC145); ERR 999 no interrupt signal from the VDP (16-IC145, 5-6-IC110, 8-12-IC125, 25-IC106). Hosted as File:Philips NMS 8250 and NMS 8255 Repair Method.pdf.
- ↑ Philips, Repair Method NMS8250/NMS8255, printed page 16, "Sum check test": the BASIC ROM (IC119) and the expansion ROM (IC118) have to be switched on with the test switch first; disk ROM IC117. Hosted as File:Philips NMS 8250 and NMS 8255 Repair Method.pdf.
- ↑ 9.0 9.1 9.2 Philips, Repair Method NMS8250/NMS8255, printed pages 21 to 23, "Floppy disk drive interface test": ERR 001 disk off line; ERR 101, 110, 111, 201, 210, 211 track 00 errors; ERR 104 and 204 track error; ERR 106 write protect error 1 (the disk's slide should be open); ERR 206 write protect error 2 (slide closed); ERR 300 busy; ERR 301 index; ERR 303 CRC; ERR 304 seek; ERR 305 write; ERR 306 write protect error 3; ERR 307 disk not ready; ERR 308 wrong side; ERR 400 FDC busy; ERR 401 data request; ERR 402 lost data; ERR 403 CRC error 2; ERR 404 record not found; ERR 405 record type; ERR 407 FDC not ready; ERR 500 media type; ERR 501 sector; ERR 503 drive data; ERR 504 track data; ERR 505 sector data; ERR 506 wrong data. Most point to IC153; the track 00, index and write-protect errors also name IC163 and IC140. Bus errors: find the faulty bus line with an oscilloscope, or put the computer in reset (tri-state) and use a voltmeter; with cartridge problems, the buffers IC165 to IC170 may be the cause. Hosted as File:Philips NMS 8250 and NMS 8255 Repair Method.pdf.
- ↑ 10.0 10.1 Philips, Service Manual NMS8250/NMS8255, PDF pages 2 and 3: FDD alignment with the FDD test cartridge 4822 397 30135 (after start-up type POKE &HFD9F,&HC9, then CALL FDDTEST) and alignment disk 4822 395 30274; FDC read-pulse width 0.5 µs (VR102) and VCO 250 kHz at TP102 (VR104). Hosted as File:Philips NMS 8250 and NMS 8255 Service Manual.pdf.
- ↑ Philips NMS 8250, MSX Resource Center wiki—link(accessed 2026-10-21) "This model is known for SCC (and other sound cards) mixing issues. There are several modifications fixing this."