Editing Sinclair ZX Spectrum +2 Troubleshooting Guide (section)

=== Finding failed chips ===

* '''Shorted RAM''' pulls down the 5 V rail. On a current-limited supply the board goes straight into limiting and the offending chips get hot — remove the hottest first. It is common to find several.<ref name="tyne" />
* '''Diagnostic ROMs''' are far quicker than manual probing. Brendan Alford's '''ZX Diagnostics''' runs from the ROM socket, tests the lower 16 K, and indicates faulty bits with beeps and coloured bars even when the display RAM itself is bad. Paul Farrow's '''128K RAM tester''' then exercises all the banks.<ref name="tyne" />
* Mixed RAM speeds and types on one board cause instability — a mixture of parts of different speed grades is not ideal.<ref name="tyne" />
* Where many chips in a bank have failed, replacing the whole bank (and socketing it) is often faster than chasing them individually.<ref name="tyne" />