Last week, I was refurbishing this ZX Spectrum for my personal collection and had just finished a composite video mod. When I went to test it, I accidentally fed 24V into the board with reversed polarity. Watching a capacitor violently blow up right in front of your eyes is certainly an unforgettable experience!
Tonight, I finally sat down to resurrect the dead Speccy. I replaced the voltage regulator, fully recapped the board, and swapped out TR4, TR5, TR7, and D1. Amazingly, it is back to life! It is currently running perfectly through a ZXHD converter. How the RAM managed to survive that voltage spike, I will never know. I even ran a full test with 48K Computer Scrabble, confirming all the memory is completely intact.
I did run into a temporary roadblock where the composite mod wasn’t outputting a picture, and I initially suspected TR1 or TR2 had blown during the power surge.
Update: I tracked the video issue down to a faulty 22µF capacitor at C25 in the video circuit. After replacing it, everything is 100% sorted and working beautifully!