Sinclair QL Service Manual
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  1. Disassembly
  2. Assembly


1.1 Access to Internal Components

1.1.1 Unplug all input/output leads and turn the QL upside down to reveal eight self-tapping screws, 4 x 5/16-in along the front edge, below the over-hang, and 4 x 1.1/4-in along the rear edge. Remove the screws (CAUTION: do not remove the two screws visible on the base immediately below the microdrives). Hold the two halves of the case together and return the QL right-side up. The top half of the case, including the keyboard, can now be separated from the bottom half, although it remains connected to it by two flexible ribbon cables and the leads from three LEDs.

1.1.2 To separate the upper and lower case halves completely, free the membrane tails from the edge connector sockets on the board by pinching them between forefinger and thumb (adjacent to the socket) and then exerting upward pressure. Release six leads from the 'snapaction' wire post socket, adjacent to the TV modulator can, by pinching the black plastic moulding between forefinger and thumb and raising it up off the board until resistance is felt; the leads can then be pulled free.

1.2 Microdrive

1.2.1 Remove the heatsink adjacent to the microdrives by releasing the attachment screw for the +5V regulator IC35; retain the M3 x 10mm screw with brass plain and crinkle washers for assembly.

1.2.2 Remove three pan-head, self-tapping screws securing the microdrive to the lower case - two visible at opposite corners of the microdrive chassis (5/16-in and 1/2-in). CAUTION: not to be confused with the countersunk motor screws and a third (3/4-in) accessible from the underside of the lower case.

1.2.3 Lift the microdrive from its mounting position and free the two ribbon cables from sockets on the board by pinching them between forefinger and thumb (adjacent to socket) and then exerting upward pressure.

1.3 Circuit Board

1.3.1 Remove both microdrives as detailed in para 1.2. Remove the reset button.

1.3.2 Release the loudspeaker leads from the 'snap-action' wire post socket, adjacent to the TV modulator can, together with two pan-head screws securing the circuit board to the lower case. The screws are located in the vicinity of the external bus connector and the loudspeaker; retain the 1/4-in screws and fibre washers for assembly.

1.3.3 Remove the push-fit microdrive extension bung from the lower case, and carefully work the circuit board free from the locating dowels by lifting it at the bus extension connector end.

1.4 Loudspeaker

1.4.1 Remove the microdrives and circuit board as detailed in paras 1.2 and 1.3.

1.4.2 Using a scalpel or similar tool, break the adhesive seal between the loudspeaker housing and the lower cover and lift the speaker from the locating dowels.

1.5 Microdrive: Disassembly for Repair

1.5.1 Stripping for repair is limited to the p.c. board, motor assembly and the microswitch. Each is secured by screws, readily identified once the microdrive is removed from the lower case.

1.6 Keyboard: Disassembly for Repair

1.6.1 Separate the upper and lower case halves as described in para 1.1.

1.6.2 Release six 1/4-in pan head screws securing the keyboard backing plate to the upper case. This allows the plate, with membrane attached, to be lifted clear revealing the keyboard bubble mat below. The membrane is separated from the plate by carefully breaking the adhesive seal holding the ribbon cables in position; the bubble mat is simply lifted from its position revealing a set of keys below.

1.6.3 Individual keys can be removed for cleaning by holding the key depressed and gently prising the retaining sleeve off the underside of the key using a small screwdriver inserted under the rim.


2.1 Assembly of the QL and its component parts is generally the reverse of disassembly. Points worthy of note are given below.

2.2 Loudspeaker. Attach double-sided adhesive tape, locate base over locating dowels adjacent to grille in the lower case and apply pressure to effect an even bond.

2.3 Circuit Board. Locate RESET button end first and once secured, replace the microdrive extension bung and loudspeaker leads. Replace reset button.

2.4 Microdrives. The ULA on the microdrive fitted in the left-hand (MDV1) position is protected by an RF shield. Ensure that the shield is in place before starting re-assembly. Start assembly by straightening the bare wire-ends of the ribbon cables and then pushing them hone in their respective sockets. Care is required to ensure the connections are made satisfactorily.

2.5 Keyboard. The bubble mat, membrane and backing plate are perforated to accommodate six locating dowels moulded in the upper case. It may prove advantageous to release the adhesive bond between the membrane and the backing plate to aid alignment.

2.6 Case Assembly. Before screwing the case halves together, reconnect the keyboard ribbon cables and LEDs to their sockets on the circuit board. The LED connections are as follows:

PinDiodeWire ColourFunction
1D21kBlackMDV2 (red)
3D20kBlackMDV1 (red)
5D27kBlackPOWER (yellow)

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