Amstrad CTM-640 Maintenance Guide
The Amstrad CTM-640 is the CPC 464's colour monitor and contains the system's only mains power supply. Its circuit, presets and alignment procedure are those of the later Amstrad CTM-644, whose maintenance guide has the full opening, supply-check and alignment procedures. The figures and lists below are the CTM640's own, from the CPC464 service manual.[1]
Safety
[edit | edit source]Warning: the CTM640 has mains voltage on its main board and a charged CRT, which can hold its charge after the set is unplugged.
- Unplug the monitor and discharge the CRT before working inside; see CRT Discharge Procedure.
- The alignment is done with the set running and the back off. Work with one hand, insulated tools and an isolation transformer.
- After any repair, Amstrad's CPC464 manual specifies a 4 kV flash test between the mains lead (live and neutral joined) and all accessible metal, and an insulation test showing at least 4 MΩ.[1] The CPC6128 manual gives 3 kV for its monitors.[2]
Opening and supply checks
[edit | edit source]Remove the four screws holding the rear cabinet, as on the CTM644.[3] The mains fuse is F501, 2 A time-lag. The only output is 5 V to the computer, set with VR501 to exactly 5 V measured across C518; Amstrad's note says this setting should not be disturbed under normal conditions.[1] Amstrad's fault chart for a dead CPC 464 checks the monitor's mains fuse, then the DC output and lead, then the computer.[1]
Alignment and voltages
[edit | edit source]The CTM640 alignment instructions on p. 23 have the same eight steps and figures as the CTM644's, with the monitor connected to a CPC464: Q802 collector at 120 V, a 145 mm paper edge with VR406, focus on the line output transformer, 5 V across C518 with VR501, and VR404 to 14,500 Hz then VR403 to 15,625 Hz.[1] The step-by-step table is in the CTM644 guide.
The voltage chart on p. 24 gives the same readings as the CTM644 chart for IC401 (LA7800), IC402 (printed as µPC1378H), IC502 (18 V in, 5.0 V out), Q404 and Q405 (collector 98.8 V).[1]
Capacitors
[edit | edit source]| Value | Circuit reference | Amstrad part no. |
|---|---|---|
| 1000 µF / 25 V | C424 | 170425 |
| 470 µF / 35 V | C402 | 1422262 |
| 470 µF / 25 V | C435, C519 | 20044 |
| 470 µF / 10 V | C518 | 170424 |
| 220 µF / 35 V | C507 | 20055 |
| 100 µF / 400 V | C505 | 170423 |
| 100 µF / 160 V | C515 | 1400246 |
| 100 µF / 35 V | C425 | 1422157 |
| 100 µF / 16 V | C412 | 20028 |
| 47 µF / 160 V | C401 | 170422 |
| 47 µF / 50 V | C512 | 170421 |
| 47 µF / 16 V | C405, C418 | 1400244 |
| 47 µF / 10 V | C436 | 170420 |
| 22 µF / 250 V | C430 | 170419 |
| 22 µF / 10 V | C437 | 170418 |
| 10 µF / 16 V | C520 | 20024 |
| 4.7 µF / 50 V | C407, C420 | 1400240 |
| 1 µF / 250 V | C506 | 1422152 |
| 1 µF / 160 V | C419 | 1422151 |
| 1 µF / 50 V | C414 | 20062 |
The CTM640 list gives C515 once, as 100 µF 160 V; the CTM644 list in the CPC6128 manual gives both 100 µF and 220 µF for that position, and its circuit diagram 220 µF.[1][4] Read the part on your own board. C505 is the reservoir on the rectified mains and must be a 400 V part. The high-voltage film capacitors are C431 (0.012 µF 1600 V), C432 (270 pF 2 kV), C513 (2200 pF 4 kV), C510 and C514 (0.0015 µF 2 kV), C511 and C801 (0.001 µF 2 kV) and C502–C504 (0.0022 µF 2 kV).[1]
Other parts
[edit | edit source]| Ref | Part | Amstrad part no. |
|---|---|---|
| IC501 | STK7308 | 170445 |
| IC502 | L78MG | 170446 |
| T501 | Switching transformer 8142004 | 170465 |
| FB401 | FB/LOPT 3714004 | 170467 |
| V001 | CRT 3701B22-TC20 | 170307 |
| F501 | Fuse 2 A (T) | 1400253 |
| TH501 | Degauss element ERP.F5BOM180H | 1400195 |
| L502 | Degauss coil | 170461 (electrical list); 170310 (cabinet list) |
| D501–D504 | Rectifier 1N4007 (printed "IN4007") | 170457 |
The two lists give different part numbers for the degaussing coil.[1]
Related pages
[edit | edit source]- Amstrad CTM-640 · Amstrad CTM-644 Maintenance Guide · Amstrad CTM-644
- Amstrad CPC 464 Maintenance Guide · Amstrad CPC 464 Service Manual
- CRT Discharge Procedure · Capacitor Failure Symptoms · Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Amstrad Consumer Electronics plc, CPC464 Micro Computer / CTM640 Colour Monitor / GT64 Green Monitor Service Manual. Described at Amstrad CPC 464 Service Manual. Safety test and specification p. 2; CTM640 cabinet drawing and parts list p. 22; electrical parts list pp. 23–24; alignment instructions p. 23; voltages p. 24; circuit diagram and PCB on the back pull-out.
- ↑ Amstrad Consumer Electronics plc, CPC6128 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual, p. 2 "Safety Test". Described at Amstrad CPC 6128 Service Manual.
- ↑ Jörg Gurowski, "Hinter Glas – Ein Blick in den Farbmonitor des CPC", CPC Amstrad International (1992). Transcribed at CPCrulez. Retrieved 2026-10-01. In German. Covers the CTM644 and CTM640.
- ↑ Amstrad Consumer Electronics plc, CPC6128 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual, CTM644 electrical parts list p. 27 and circuit diagram pp. 29–30. Described at Amstrad CPC 6128 Service Manual.