Editing Sinclair QL Maintenance Guide (section)

== Keyboard ==

The QL keyboard is a membrane under a rubber bubble mat, in an 8 × 8 matrix with partial diode isolation, connected to the board by two flex tails at J11 and J12.<ref name="sm" /> It is a wear item, and the usual failures map cleanly onto symptoms:

{| class="wikitable styled-table" style="width:95%; text-align:left;"
|+'''Keyboard symptom to remedy (Service Manual)'''
! Symptom !! Remedy
|-
| Keyboard does not respond at all || Check connectors J11 and J12 and the ribbon cable
|-
| Multi-character printing, key bounce, keys sticking down, a key does not register || Renew the membrane
|-
| A key does not ''always'' register || Renew the bubble mat
|-
| "Sticky" keys || Clean the key surfaces; renew the bubble mat
|-
| Continues to fail the keyboard test || Renew IC24 (IPC), then IC18 (CPU)
|-
| Keyboard locks up after prolonged use || Renew IC23 (ZX8302), then IC24, then IC18
|}

Source: Service Manual fault-finding guide.<ref name="sm" />

'''Membrane tail repair.''' A common fault is a break in the membrane close to the connector. If the break is near the tail end, the ribbon can be removed from the connector, a short section sliced off above the break, and the shortened tail plugged back in.<ref name="sm" /> Cleaning the tail ends and the sockets is worth doing routinely — dirty or damaged tails cause lock-ups and dead keys.<ref name="tfs" />

Individual keycaps can be pulled for cleaning. When refitting a membrane, make sure both tails are fully inserted and not kinked.<ref name="sm" />