Hard to find a fault like that, and resistors don’t often fail. Can’t really test them in circuit, by the time they are removed for test it’s faster to just replace them. I’ll bet it was a good moment to get this working! Nothing like that “ah” after a battle hard fought.finally after a lot of work i discovered the defect in the audio that was causing problems in the sound of kicks, voices etc. after changing oki chip, z80, all capacitors, 4 ci 5218a, ci yamaha ym2151, chip ym3012 among others, I found that the defect was simply resistor R47 (2.2k). problem solved and sound working perfectly.