Editing Amstrad CTM-644 Maintenance Guide (section)

== Supply checks ==

{| class="wikitable styled-table" style="width:70%; text-align:left;"
|+'''CTM644 supply'''
! Rail !! Expected !! Source in the set
|-
| Mains input || 240&nbsp;V AC 50&nbsp;Hz through F501 (2&nbsp;A time-lag) || SW501, F501, line filter L501, bridge D501–D504, reservoir C505 (100&nbsp;µF 400&nbsp;V)
|-
| 5&nbsp;V to the computer || Exactly 5&nbsp;V across C518, set with VR501 || IC502 (L78MG); IC502 pin 1 at 18&nbsp;V, pin 4 at 5.0&nbsp;V in the voltage chart
|-
| 12&nbsp;V to the disc drive || 11.8&nbsp;V at the regulator output in the circuit diagram || IC503 (µPC78M12), 16.5&nbsp;V at its input
|-
| CRT drive || 120&nbsp;V at the collector of Q802 with brightness at maximum, set with VR402 || Alignment step 7
|}

Amstrad's note on the 5&nbsp;V adjustment says it should not be disturbed under normal conditions.<ref name="sm6128" /> ''CPC Amstrad International'' measures the 5&nbsp;V at the monitor's 5&nbsp;V supply socket and allows a deviation of no more than −0.1&nbsp;V.<ref name="cpcai" /> If the 5&nbsp;V is missing but the screen works, check the 5&nbsp;V lead and plug before the supply. If the computer runs but the drive does not, measure 12&nbsp;V at the jack J501.