AnsweredAssumed Answered

ESG-DP Cooling Problem?

Question asked by swperk on Jul 6, 2011
Latest reply on Aug 10, 2011 by tabbott
I've been working on an E4436B ESG-DP that works fine when cold but loses PLL lock at the whole GHz frequencies (1 GHz, 2 GHz, and 3 GHz) once it's warmed up a bit. The PLL unlock range extends only a few MHz lower than the whole GHz frequency, i.e., below about 980 MHz, 1.98 GHz, 2.98 GHz the output is again locked and clean. Even the smallest frequency shift (e.g., 10 millihertz) above 1 GHz and 2 GHz causes immediate PLL lock with clean output. I thought this was a temperature-induced problem with the synthesizer, since cooling off the side card cage with freeze spray got rid of the problem, albeit temporarily.

On further investigation, it seemed to me as though the two 12 volt cooling fans were not moving a lot of air, and, in fact, when I measured the voltage across the fans, it was only 7.5 volts, increasing if I disconnected one or both fans (12 volts with both disconnected). The 12 volt side of each fan connector is at 12 volts WRT chassis ground, but the negative terminal of the fan connector floats up from 0 volts to around 4.5 volts with both fans connected.

It seems as though the 12 volt fans ought to be getting 12 volts, but could this in fact be normal behavior? Is there some sort of temperature-based regulation of the fan voltage? If not, is there a simple fix?