Just suppose one TTL IC is shorted in a mess of 35 or so. When you turn on power the 5V supply goes into current limit. How would you find the bad chiP.
I told you about binary searching without telling you the term. Linear means you start at stage one and continue incrementing by a "stage" until you reach 10. Bisecting or binary searching is all about bisecting the faulty sections.
If you guys are troubleshooting a lot of similar boards, you should have some of these on the bench:
https://www.huntron.com/products/2800.htm
With a good and bad board side by side, it should be easy to find the faults, unpowered even.
Multi-voltage supplies typically have dependencies. You have to be aware of them.
You guys should also invest in an IR camera that can be shared. A very expensive, but useful piece of equipment.
If your troubleshooting the same stuff and see lots of the same stuff, then you should be doing some sort of failure analysis with those boards. The symptoms should suggest possible failures even before you start.
You might want to take a look at some older Keithley, Tektronix or HP/Agilent service manuals to get an idea as to how they should be written.
When I was troubleshooting an early Scanning Electron Microscope, the most useful thing was the card extender. It was mostly 741 OP amps, but it was really easy to fix.
When I was dealing with a Kevex Auger mass Spectrometer, that was WAY different. Only schematics.
When i was dealing with DC power supplies and vacuum gauges, nearly everything could be fixed by knowing the symptoms. Relamping was done last. If the guage didn't turn on, there were 1 of 2 problems: ripple on the -15 V supply or a bad relay for the filament. It's like, those were the only issues unless someone spilled acetone on the meter face. Then there was calibration.
A DC power switching supply would basically get very noisy. Replacing about 8 or 9 capacitors would fix it every time.
A lot of other recurring problems were due to surges that were either power line related or loose internal connections. One had to do with non-isolation of a 100 kV power supply. Those I had to engineer fixes.
Many of the maintenance issues I had to deal with were also mechanical. Disk drives, fans, slidewires, potentiometers etc.
I did a fair number of repairs to high powered audio amplifiers. That takes some skill, because not catching a bad part takes out all of the new parts.
One of the most stupidest problems I had to deal with was a SBC (Single Board Computer) that would not reset when using a linear power supply. It worked fine with a switching power supply for power. Annoying, for sure. I just replaced an IC with a Schmidt Trigger version and fixed.