Aircraft? It makes sense now.
Anyway, I looked at the U19 and U20 stuff and I'll bet the transistor goes to leds and to a +24 V supply.
So, you really have one easy test to make. Do a lamp test with lamps present and check the B-E junctions of the transistors. Without the LED's, it's gonna be tough to troubleshoot.
The S/R FF's have some sort of Reset and they latch an error condition.
That should be relatively easy to troubleshoot, although R is a pulse and is common, so any fault on that line could mess up all of the IC's. S is a momentary input.
The inputs on R & S have to have nice edges.
Anyway, I looked at the U19 and U20 stuff and I'll bet the transistor goes to leds and to a +24 V supply.
So, you really have one easy test to make. Do a lamp test with lamps present and check the B-E junctions of the transistors. Without the LED's, it's gonna be tough to troubleshoot.
The S/R FF's have some sort of Reset and they latch an error condition.
That should be relatively easy to troubleshoot, although R is a pulse and is common, so any fault on that line could mess up all of the IC's. S is a momentary input.
The inputs on R & S have to have nice edges.