Editing Sinclair ZX Spectrum+ (section)

== Which board is inside? ==

The Spectrum+ case was used with several different 48K board issues, and knowing which one you have matters for fault-finding:<ref name="sfe" />

{| class="wikitable styled-table" style="width:70%; text-align:left;"
|+'''48K board issues found in the Spectrum+ case'''
! Issue !! Notes
|-
| '''4A / 4B''' || The first issue widely available in the Spectrum+ case. Uses the 6C001E-7 ULA, incorporates earlier DC-DC converter service modifications directly on the PCB, and routes /RAS through spare inverters to delay the signal — which is why Issue 4A and 4B boards '''will not work with IC24 removed''', unlike earlier issues. Some were made on yellow SRBP laminate. Includes provision for the aborted US FCC certification (modulator channel switch, EM suppression coils, case grounding points).
|-
| '''4S''' || Samsung-manufactured, almost identical to Issue 3B (it does not route /RAS through IC24). Green solder mask both sides, extra solder pads for alternative components. Serial numbers begin '''S01'''. The keyboard membranes supplied with these machines are of noticeably better quality and many still work today.
|-
| '''5''' || Only about 1,000 made, and none were known to survive until recently. Has a layout error requiring a PCB modification and patch wiring. First issue to use the ZX8401/PCF1306P, which replaced six 74-series logic ICs but introduced timing problems needing an extra 74LS04.
|-
| '''6A''' || The final 48K PCB issue — effectively a bug-fixed Issue 5. Supports the AMI SAGA-1A ULA as an alternative to the Ferranti part, though only one surviving machine with an AMI ULA is known. Has dedicated provision on the PCB for the reset switch, instead of the switch being wired across C27 as on earlier issues fitted in Spectrum+ cases.
|}

[[File:Sinclair ZX Spectrum Plus main board Issue 6A.jpg|center|thumb|620px|A Spectrum+ Issue 6A board in its case. The Astec modulator is top left, the 7805 regulator and its heatsink centre, with the ULA, Z80A, ROM and the two rows of RAM below. The white wires are the reset switch.]]