I got the HP 1607A, which was previously non-functional, up and running!
I opened up the machine today and poked around looking for faults in a power rail, but upon first look every rail seemed ok. The voltage rails +5v, +12v, and -12v all looked fine.
The next step was to understand why the Z-blanking signal which is output at the rear of the machine was missing… I spent the next fifteen minutes or so tracking backwards until I found the source of the problem which was a missing 100 khz clock. The issue was some issue in this circuit:
It turns out that 5Vf was missing. I tracked it back to an earlier schematic page and it appears to be sourced from an inductor.
I grabbed my soldering iron and swapped this guy out…
That was it!
The HP 1607A was back in business!
MicroCore Labs 