Editing Amstrad CTM-644 Maintenance Guide (section)

== Safety ==

'''Warning: the CTM644 contains mains voltage on its main board and a CRT charged to several kilovolts, which can hold its charge after the set is unplugged.'''

* Unplug the monitor from the mains before removing the back. Discharge the CRT as described in [[CRT Discharge Procedure]] before touching the board or the anode lead.
* Amstrad's alignment steps are made with the set running and the back off. ''CPC Amstrad International'' warns that contacts on the board carry mains voltage during this work.<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. Opening the set, the home alignment procedure with BASIC test programs, the 5&nbsp;V tolerance and the convergence magnets.</ref> Use one hand, insulated tools and an isolation transformer; Amstrad's later Plus-range monitor manual calls for an isolation transformer for any service on its monitors.<ref name="smplus">Amstrad plc, ''464 PLUS / 6128 PLUS / GX4000 / MM 12 / CM 14 Service Manual'', MM12 and CM14 electrical adjustments, pp. 37 and 44. Described at [[Amstrad 464 Plus / 6128 Plus / GX4000 Service Manual]].</ref>
* After any repair, Amstrad's manual specifies a 3&nbsp;kV flash test between the mains lead (live and neutral joined) and all accessible metal, and an insulation test showing at least 4&nbsp;MΩ between the same points.<ref name="sm6128" /> Parts marked with a warning triangle on the circuit diagram are critical for safety and must be replaced with the parts listed.