Tektronix 495P Spectrum Analyzer Repair
I recently acquired two Tek 495P spectrum analyzers. One is in mint condition and performs in accordance with the initial checkout procedure in the user manual. The second unit came along with the first as a freebie “parts” unit. In booting up this unit I find that it is working to a substantial extent but has a couple of issues. Hoping the pros here can provide some insight into next steps for repair.
Both 495s are late serial number units (sn B030xxx in both cases). When the parts unit boots up, it posts a message on the screen identifying the firmware version as “492AP v9.7 panel v1.1,” not 495. In reviewing the service manual and other info from various online resources, I see that the firmware in the 49x series is somewhat generic, with DIP switch settings on the A54 memory board determining which model version of the firmware actually runs following boot up. I have verified that these DIP switch settings are as specified in the service manual. I have also verified that the DIP switches themselves are working properly, and that the correct EPROMs (v9.7) are installed on the board. (There are also DIP switches on the Z-axis board, which are verified to be in the correct positions.)
The seller reports that the memory board may have been damaged when removing the memory backup battery for replacement, or that the board may have been damaged by a leaking battery. I see no evidence of damage, however, the battery leads show some evidence of solder work and it appears that soldering on the plated through hole on one of the battery leads is questionable. In looking at the circuit diagram of the memory board, it is not apparent why a poor battery connection would produce the symptoms I am seeing. Unless someone here has a better idea, my next move is to try to purchase another memory board.
The other issue is an error message stating “Tuning failure – 1st LO.” The 492AP and 495 share a common controller architecture but differ significantly in the analog/RF circuitry, with the 492AP having a freq limit of 21 GHz, while the 495 is 1.8 GHz. It seems somewhat likely that the 492AP firmware in attempting to tune a 495 1st LO is having problems doing so. I would not be too surprised to find that this error goes away once the unit is running the correct firmware.
I have a long, strong electronics background, but am a newbie when it comes to SAs. Any insights much appreciated.
Rick
K8EZB