Editing Amstrad CTM-644

{{Infobox computer peripheral
| name         = Amstrad CTM644
| image        = [[File:Amstrad CPC 664 with colour monitor.jpg|260px|frameless]]
| caption      = CTM644 colour monitor with a CPC 664
| manufacturer = Amstrad Consumer Electronics plc
| type         = Colour monitor and system power supply
| interface    = 6-pin DIN (RGB and sync), 5&nbsp;V DC lead, 12&nbsp;V DC socket
| compatible   = [[Amstrad CPC 664]], [[Amstrad 6128|Amstrad CPC 6128]], [[Amstrad CPC 464]]
| power        = 240&nbsp;V AC 50&nbsp;Hz
| dimensions   = 375 × 340 × 365&nbsp;mm
| weight       = 10.6&nbsp;kg
| predecessor  = [[Amstrad CTM-640]]
| model        = CTM644
}}
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The '''Amstrad CTM644''' is the colour monitor Amstrad sold with the [[Amstrad CPC 664]] and [[Amstrad 6128|CPC 6128]]. Like the [[Amstrad CTM-640]] it holds the whole system's mains power supply: the computer has no mains input and takes 5&nbsp;V from the monitor on a lead. The CTM644 adds a 12&nbsp;V output for the disc-drive models, on a socket that takes the computer's 12&nbsp;V lead.<ref name="sm6128">Amstrad Consumer Electronics plc, ''CPC6128 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual''. Described at [[Amstrad CPC 6128 Service Manual]]. Safety test p. 2; CTM644 cabinet drawing and parts list p. 26; electrical parts list and alignment instructions p. 27; parts list and voltages p. 28; circuit diagram pp. 29–30; main PCB pp. 31–32; technical specification on the back page.</ref><ref name="wpcpc">Wikipedia, [https://en.wikipedia.org/wiki/Amstrad_CPC "Amstrad CPC"], section "CPC 664". Retrieved 2026-10-01. The 664's disc drive needs 12&nbsp;V, supplied by the updated GT-65 and CTM-644 monitors.</ref> A 1992 article in ''CPC Amstrad International'' describes the CTM644 and CTM640 as differing only in that 12&nbsp;V supply.<ref name="cpcai">Jörg Gurowski, "Hinter Glas – Ein Blick in den Farbmonitor des CPC", ''CPC Amstrad International'' (1992). Transcribed at [https://cpcrulez.fr/hardware_dossier-ctm-ein_blick_in_den_farbmonitor_des_CPC_AI.htm CPCrulez]. Retrieved 2026-10-01. In German. Construction of the CTM644, the difference from the CTM640, and a home alignment procedure.</ref>

The CTM644 contains a CRT and a mains switch-mode supply. Read [[CRT Discharge Procedure]] before opening it.

== Specifications ==

{| class="wikitable styled-table" style="width:70%; text-align:left;"
|+'''CTM644 (CPC6128 service manual)'''
! Item !! Value
|-
| Mains supply || 240&nbsp;V AC 50&nbsp;Hz, double-pole switch SW501
|-
| Mains fuse || F501, 2&nbsp;A time-lag (part 1400253)
|-
| Outputs || 5&nbsp;V to the computer (adjusted with VR501); 12&nbsp;V for the disc drive from IC503
|-
| Video input || 6-pin DIN lead: red, green, blue, sync and ground
|-
| CRT || V001, 3701B22-TC20 (part 170307)
|-
| Line output transformer || FB401, 3714004 (part 170467)
|-
| Line frequency || 15,625&nbsp;Hz (H. hold alignment)
|-
| Dimensions, weight || 375 × 340 × 365&nbsp;mm, 10.6&nbsp;kg
|}

The figures are from the parts lists, the circuit diagram, the alignment instructions and the back-page specification of the CPC6128 manual.<ref name="sm6128" /> The CPC 664 manual covers the same monitor.<ref name="sm664">Amstrad Consumer Electronics plc, ''CPC664 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual''. Described at [[Amstrad CPC 664 Service Manual]].</ref>

== Power supply ==

The supply is on the main board. The circuit diagram shows the mains entering through SW501, the time-lag fuse F501 and the line filter L501, a bridge of four 20E10 rectifiers (D501–D504) charging C505 (100&nbsp;µF 400&nbsp;V), and a switch-mode converter built around the STK7308 hybrid (IC501) and the switching transformer T501 (8142006). The degaussing coil L502 is fed through the thermistor TH501.<ref name="sm6128" />

The 5&nbsp;V output is regulated around IC502 (L78MG) and set with VR501, measured across C518, to exactly 5&nbsp;V. The 12&nbsp;V output comes from IC503, a µPC78M12 regulator; the circuit diagram shows 16.5&nbsp;V at its input and 11.8&nbsp;V at its output, with C522 (470&nbsp;µF 35&nbsp;V) and C523 (100&nbsp;µF 16&nbsp;V) either side.<ref name="sm6128" /> The CTM640 has neither IC503 nor the 12&nbsp;V socket.<ref name="sm464">Amstrad Consumer Electronics plc, ''CPC464 Micro Computer / CTM640 Colour Monitor / GT64 Green Monitor Service Manual'', pp. 22–24. Described at [[Amstrad CPC 464 Service Manual]].</ref>

== Controls and connections ==

* User controls: the power button (SW501) and the brightness control (VR401, 500&nbsp;Ω).<ref name="sm6128" />
* Leads: the 5&nbsp;V DC cord (CD005) and the 6-pin DIN cord (CD007) to the computer; the 12&nbsp;V jack J501 for the computer's disc lead.<ref name="sm6128" />
* Inside: the vertical hold VR405 (20k), the service/normal switch SW401 used during alignment, the focus and screen controls on the line output transformer, and the presets listed in the [[Amstrad CTM-644 Maintenance Guide]].<ref name="sm6128" />

== Board revisions ==

Amstrad's amendment manual reissues the CTM644 parts list for a later chassis. It lists a different CRT (A34JLL70X10, part 170307-A), a different line output transformer (3714009, part 170468), IC protectors ICP501 and ICP502, and changes several capacitor values (C518 from 470&nbsp;µF to 1000&nbsp;µF at 10&nbsp;V, C405 from 47&nbsp;µF to 470&nbsp;µF at 16&nbsp;V, C512 from 47&nbsp;µF to 100&nbsp;µF at 50&nbsp;V), and raises the sub-brightness setting from 120&nbsp;V to 123–124&nbsp;V.<ref name="amd">Amstrad plc, ''CPC464 / CPC6128 / GT65 / CTM644 / MP3 / CT1 Amendment Service Manual'', CTM644 section pp. 27–30. Described at [[Amstrad CPC 464 / CPC 6128 / GT65 / CTM644 / MP3 / CT1 Service Manual Amendment]].</ref> Its alignment remarks refer to the monitor connected to a CPC464, and the manual's title groups the CPC464 with the GT65 and CTM644.<ref name="amd" /> Check which parts list matches your board before ordering parts.

== Faults ==

Amstrad's basic hardware analysis for the CPC 6128 starts with the monitor: no power LED on the computer means checking the monitor's mains fuse and the 5&nbsp;V on the cable from the monitor; a computer that starts but shows no picture is tried on another monitor, and if it works there the suspects are the monitor's cable termination, internal connectors and brightness control.<ref name="sm6128" /> Diagnosis, the voltage chart and the alignment procedure are in the [[Amstrad CTM-644 Maintenance Guide]].

== Documentation ==

* [[Amstrad CPC 6128 Service Manual]] – CTM644 parts lists, alignment, voltages, circuit diagram and PCB (pp. 26–32)
* [[Amstrad CPC 664 Service Manual]] – the same monitor with the CPC 664
* [[Amstrad CPC 464 / CPC 6128 / GT65 / CTM644 / MP3 / CT1 Service Manual Amendment]] – the later chassis

== Related pages ==

* [[Amstrad CTM-644 Maintenance Guide]] · [[Amstrad CTM-640]]
* [[Amstrad 6128|Amstrad CPC 6128]] · [[Amstrad CPC 664]]
* [[CRT Discharge Procedure]] · [[Capacitor Failure Symptoms]]

== References ==
<references />

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[[Category:Amstrad]]