Really interesting piece, thanks for sharing this series! The build is very HP-'ish and obviously high quality. No service manual is a big impediment to understanding it obviously, but your approach is solid from where I sit. I can't offer too much experience, but I have saved a couple pieces of a similar nature and era. One particular puzzle on an HP signal Generator, taught me that even if the rails seem to test good, a regulator could have a failure mode that only occurs when it's under load from the circuit. That condition can cause all kinds of seemingly unrelated effects. I'd test each one under load to verify it's in spec. Looking forward to seeing you get this in working order! Thanks again for great content. - jrh
