I used to work as a line tech on these back in 1980.? The things I most remember about them was the .01dB level accuracy and the millihertz frequency resolution were just amazing.? I also remember they were sometimes a nightmare to turn-on and calibrate on the line as they would have spurious oscillation and "wandering spur" issues that sometimes required adding additional ferrite beads that weren't on the schematics or BOM as most units didn't need them.? Also the fractional-N digital circuitry was a real bear to troubleshoot.? The good part was once you worked out the occasional issues, they were a very solid machine.? But there would be one now and then that was your nearly invincible enemy.
? The 3325A later came out with a lot of the Fractional-N circuitry on a single ASIC, I really envied the guys that worked on them.
? I would not call this unit hard to service or a poor mechanical design.? Pull the big aluminum hunk and you have lots of access!? The synthesizer module has 3 long bolts holding it in.? Remove the SMA Semi-rigid coax cable from the module's backplane then pull the 3 screws in the middle and you can lift the synth module and set it aside with the other cables plugged in IIRC.? There are even legs to set it on!? Don't block the honeycomb vents or run it flat out of the chassis, there is some power hungry digital in there.? Then you can much more easily access the power supply to probe more of it.? I only worked on new units for the most part so I don't know what fails after 40+ year.? I'd suspect wear out / age related issues and cracked solder joint failures on power devices.
? We had a test fixture with some load resistors for testing the supplies when there was a problem.? I would tend to do the power supply diagnostics (rarely needed) with the synth module disconnected to avoid damaging it while working the supplies.??
? There was a series of 4? troubleshooting videos, too long for me to want to watch but I think he had some power supply issues.? Search YouTube for 3335A repair if interested and you should find them.
? The 3335A was the unit that convinced me to move to the Integrated Circuit Wafer Fab later in 1980 and tackle high vacuum systems and all the dangerous voltages and chemicals.? I liked that work more than that wonderful but sometimes really hard to repair aluminum block of bleeding edge tech.? I also worked on the 3551A, the 3312A, and in the R&D lab on the 3314A for a while, plus some temporary work on other sources as needed.
Clay Scott
