24-11-2016, 11:50 AM
Hmm - 0.6V on the collector of Q24 simply confirms that Q24 is switched on. Which we know because the LED is on 
If a 15V rail is missing, that would certainly explain some weirdness. Having said that, I can't immediately guess how that gives the symptoms, but either way, let's see what we've got once it's been replaced.
For testing, if you had a 7812 in stock, that might do the job while you wait for the correct replacement. Or a 7805 with a 10V zener in the ground terminal. Or a bench PSU?
In the meantime, I wonder why that regulator failed? Sometimes they jump, but often they're pushed
If a 15V rail is missing, that would certainly explain some weirdness. Having said that, I can't immediately guess how that gives the symptoms, but either way, let's see what we've got once it's been replaced.
For testing, if you had a 7812 in stock, that might do the job while you wait for the correct replacement. Or a 7805 with a 10V zener in the ground terminal. Or a bench PSU?
In the meantime, I wonder why that regulator failed? Sometimes they jump, but often they're pushed
