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

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

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

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

**CTM640 electrolytic capacitors (CPC464 service manual p. 23)**
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

**CTM640 parts (pp. 22–24)**
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

References

↑ ^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.

[sm464-1] 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.

[sm6128-2] 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.

[cpcai-3] 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.

[sm6128b-4] 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.

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