WB0SMX

  8640b FM Deviation Pot Repair Filed in 8640b , Test Equipment on Oct.17, 2016 After replacing the gearset in my 8640b signal generator, the next item on the list was to repair the FM Deviation potentiometer, which had the shaft broken off where the knob would attach to the front. Since the pot is still electrically good, and I cannot locate another pot with the same value and length of control shaft, I thought that I could somehow repair the shaft. My first attempt at this was to remove the old shaft at the potentiometer body, and replace it with a longer one. It looked like I could remove the retaining clip near the pot’s body, and perhaps the shaft would pull out. Unfortunately, after removing the retainer clip, the shaft remained held to the body, so that did not pan out.   FM Deviation potentiometer I put the retainer clip back on the shaft and proceeded with Plan B. Plan B was to add a section of 1/8″ rod to the front of the shaft, using some mechanical fitting an

  HP 8640b Signal Generator Gear Set Replacement Filed in Test Equipment on Oct.09, 2016 Back in April of 2016, I bid on a Hewlett Packard 8640b signal generator to upgrade my test bench at home. This was from a local seller, and I won the bid for $115.00 + $20.00 shipping, for a total of $135.00. I figured for that price, I couldn’t go wrong. In working condition, these typically run about $500.00, depending on condition. When the unit arrived, it was not packed great (they used packing peanuts, instead of snug foam), but it was double boxed, and there appeared to be no damage in shipping. I plugged in the unit and brought it up slowly on the variac, in case there were shorts that might cause further problems in the unit.  To my surprise, the unit came up and appeared to mostly work. I could not turn the FM Deviation knob through all of it’s ranges, and the generator indicated that the deviation was out of allowed limits when I turned the FM modulation on. Also, the F