Uploaded June 2026 | Updated September 2026, 2 weeks ago

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I built a ZX Spectrum diagnostic ROM cartridge using a 27C512 EPROM, a 74HCT32 logic chip and a two-switch ROM bank selector.

This external ROM board lets a ZX Spectrum boot from four different 16K ROM images, selected with DIP switches, so it can be used for diagnostics, repair testing and a few small cartridge games as well.

In this build I solder the PCB, modify the edge connector, prepare the ROM image, program the EPROM and test it on a rubber-key 48K ZX Spectrum.

Sponsored by PCBWay, who supplied the PCB for this video.

PCBWay:
pcbway.com

PCBWay Instant Quote:
pcbway.com/orderonline.aspx

PCBWay Shared Project:
pcbway.com/project/shareproject/ZX_Spectrum_diagnostic_ROM_173af101.html

Project credit:
Skoti / ZX External ROM
github.com/konkotgit/ZX-external-ROM

ROM credits mentioned in the video:
ZX Diagnostics by Brendan Alford, based on work by Dylan Smith
Retroleum DiagROM by Phil Ruston
Mag the Magician by Radastan

CHAPTERS:
00:00 ZX Spectrum diagnostic ROM cartridge
00:22 PCBWay sponsor and project credit
00:45 Parts for the build
01:48 Edge connector problem
02:13 Soldering the first components
03:05 LED resistor and pull-up resistors
03:38 What flux does
04:29 DIP switches and power LED
05:07 EPROM socket
06:31 74HCT32 logic chip
07:02 Fitting the edge connector
08:31 Preparing the ROM image
09:27 Programming the EPROM
10:03 Installing and testing the chips
10:51 Testing on a 48K ZX Spectrum
11:16 ZX Diagnostics ROM
11:53 Jetpac from ROM
12:22 Retroleum DiagROM
12:55 Mag the Magician
13:19 Fixing the power LED
13:37 Patreon and wrap-up

#zxspectrum #retrocomputing #electronicsrepair