Hi Mike and ALL here and I wish you all a Happy New Year from Australia.
Some of the diagnostic tools I use on older Motherboards and PCBs apart from a Trusty old MOVING POINTER AVO Multimeter, its way more valuable at times than a modern digital one, are
1. HP 545A Logic Probe switchable for either TTL or Cmos
and
2. HP 546A Logic Pulser that has 3 variation pulses 1 pulse at 10hz. then 100Hz burst of 10 pulses, or 100 pulse burst at 1Hz duration. Runs from 3 to 18volts DC
Both have power leads that have socket ends that can have fine spring loaded clips to go around IC legs, or can plug on to pcb pin headers to get their needed power.
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1976-12.pdf
3. is a small Tektronix AC current probe P6022 that connects to one of my Oscilloscopes or a multimeter using a suitable BNC to pin and inductance adaptor
4. an even smaller Tektronix Current Probe CT-2 that has a tiny hole to pass a resistor or capacitor leg though.
Ok it requires unsoldering one end of said type components and add a tiny flying lead. if I am worried about desoldering a PCB, I may choose to very carefully snip the component leg and use flying lead to both ends. Then after test carefully repair the cut with small length of spare 1/4w resistor leg soldered across the cut.