All I saw was board schematic for Jackson II and Jackson - but not like the board in SP5IT photos. That was in 1995 - so went on what I would approach on this.
Low Boy...
ASC is Automatic Squelch Control.
A really simple circuit - a Diode, Resistor and or maybe a cap - but in an HR2510 it's the AUTO on the Squelch control - turn it all the way to the left, it'll click. When on, it works like you set squelch - takes care of some noise on the frequency, but any loud noisy RF area - it'll pop open and all you hear is the noise - it's not perfect - just a convenience. (HR2510 - Look for D175 ) - it sends 8 volts "pre-set" by a 2.2K resistor into the Squelch circuit - so that is the "preset" and it also uses the "SQ Trimmer" feeder line - so any air noise the radio generates as part of the tune up SQ setting is adjusted for - is already added in.
RF Gain affects it too.
IT "pre-sets" for FM hash noise - in helps silence the speaker when you're in FM mode. Works on AM too in the earlier Jackson versions - but not as well. Not very effective on SSB. It'll work on all modes in the HR2510 - in the 2010 Jackson - it's CPU triggered - and only works in FM - so when you set "Auto" it isn't silencing a speaker in the other modes you would not normally need it.
There's an LED lite that turns on so when the radio is too quiet, check the S/RF meter - you may be missing a call.
ASC is a neat feature, not perfect, but neat.
:+> Andy <+: