Follow-up: as several time-nuts noted, there was a lot of corrosion on parts of the lamp module. Oddly, there was no corrosion on the rest of the PRS10, or on the TS2500 which it came out of. The resistor lead was severely oxidized and partly melted. It's possible that the inductance of the wire-wound resistor helped sustain an arc. Alternatively, the grounded lead may have arced to the hot end of the lamp drive coil, although the coil itself showed very little damage. Perhaps ozone from an arc accelerated the corrosion. Dunno, it's a mystery.
The resistor is specified at 2W, but it's much smaller than a typical 2W resistor. I removed the damaged lead and replaced it with a bit of 16 AWG magnet wire. This gave mechanical support as well as an electrical connection. Buttoned it all back up and applied power, and the lamp lit almost immediately (it wasn't lit before) and it locked quickly. Tuned it to match a GPSDO, and it seems to be working fine. A note on tuning: the documentation says that the "SF" tuning command has a resolution of 1E-12. That's true, but the actual available tuning resolution seems to be more like 1E-11. The actual tuning is done by adjusting the C-field with a 12-bit DAC. The "MR?" command gives the present value of that DAC. Unfortunately, the full range of the SF command (4000 counts) only moves the DAC about 600 counts. You can increment the SF command several times before seeing a response. Anyone planning to use a PRS10 inside a control loop should be aware of this quirk. Cheers! --Stu _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.