Don't forget to check the op-amps in the LV PS. Often, they are seated in bad sockets (TI) or their contacts have deteriorated with time. Reseating often helps in such cases.
I've seen dead ones as well. Since they're very cheap, you might choose to just replace them.
If you don't have any replacement available, you could swap/interchange U1418, U1454 and U1464, since they all are the same type.
+ 50 V is up, so U1418 should be OK. You may lose + 50 V if you swap in a defective chip in its position. Might be a good check for the others.
It's likely that you'd still be able to identify a bad chip in the absence of known-good r(new) replacements. Remember though that + 50 V needs to be up for any of the others to work.
Obviously, it's far preferable to just get a few new chips and put them in. Would cost you less than 1 USD for 3 pcs.