Showing posts from November, 2016

8640b Power Supply Repair

  8640b Power Supply Repair Filed in 8640b on Nov.02, 2016 Early in the repair cycle of the 8640b, when I had just finished the brass gearset installation, I ran into a problem during the first power up after reinstallation of the deviation and range module. When I powered up the unit, I saw a flash from under the main board, and the unit came up with no led frequency display. I suspected that I had lost one of the power supplies. After finding the manual for the generator, I saw that there were 3 power supply boards with led indicators on them to indicate the various voltages were being generated.   5v indicator I found that the 5v indicator was not lit. Looking at the schematic of the board, I tracked down that it should have some relatively high voltage DC coming in on pins 15 and 9 of the module ( or pins 1 & 2 of the rectifier module). It had nothing coming in. I saw in the schematic that it was fed from a rectifier board. Since this had easy access, I pulled t

8640b Fine Tune Repair

  8640b Fine Tune Repair Filed in 8640b on Nov.01, 2016 Another item on the 8640b refurbishment project was the broken Fine Tune control. I could rotate the control from the front panel, but it had no effect on the frequency generated. After removing the bottom cover, I could see the problem. The Oscillator Module was missing the shaft that connected the fine tube knob with the control on the rear of the main oscillator   Shaft missing The shaft should be near the top of the picture above. I started the repair by removing the Main and fine tune knobs.   Main and Fine Tune controls     Knobs removed There is a module beside the main oscillator that needs to be removed, as it is connected to the wires from the back of the main oscillator. I just removed the two nuts/washers securing it, and pulled it up out of its card slot (it has an edge card connector). Then, it will lift out with the rest of the main oscillator module.   Loose module Next, I loosened the 4 screws securi