I’ve finally got it working. I decided to give it a thorough clean on both sides, before I progressed any further, and while doing so noticed R636 had broken away from its solder joint. I finished the clean, resoldered the resistor and tried the voltages again. All was now clear. Tbh I don’t know if R636 was always the problem, or if I damaged it while cleaning and the cleaning itself fixed the problem. 
Either way I’m chalking it up as a fix!
Thanks again to all who gave advice and tried to help. No doubt I’ll be back soon!
Either way I’m chalking it up as a fix!Thanks again to all who gave advice and tried to help. No doubt I’ll be back soon!
