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We have two Sinclair ZX Spectrum+ computers with REALLY bad video image quality. This is a pretty frequent fault and is usually caused by bad electrolytic capacitors generating unstable voltages inside the computer. Here we learn how to diagnose and fix the bad video quality caused by the capacitors.
We take a good look at the voltage-generating circuitry inside the Spectrum (it generates +12V, +5V, and -5V from a 9V DC power supply) and try to understand how it all works. Then we take a look at the voltage signals with the oscilloscope and confirm that the electrolytic capacitors are most likely faulty.
Finally, we replace all the electrolytic capacitors, measure everything again, and test the final image quality and compare it to how it was at the beginning.
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