Any advice appreciated
Did it work ok before changing the caps?
Did you change all of the caps in one go or did you do a couple and then test, and repeat until all are done? I.e. do you know changing which caps caused the issue? If so then look for damage / unwanted solder in that area.
Obvious one but have you fitted them all using the correct polarity? Its easy enough to put one in the wrong way round. I know this from experience.
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Rule #2 of modding: if after that you find machine doesn't work anymore, it will be because of whatever was modified just now. Double-check, triple-check, or undo if necessary.
Sure there's ESD, pcb tracks where a crack develops while you're working on the board, etc. But in practice, I have yet to encounter a case where the above doesn't hold. Don't modify a machine which you don't know whether it works. Unless it helps to make a repair easier (composite video mod comes to mind).