I need help with Tektronix 2710 spectrum analyzer...
It's having some frequency domain fault above 1 GHz. Infact there are no exact point where the fault begins: sometimes it will work even to 1.3 GHz but there's a days when even 800 MHz is too much for it... However with lower frequencies (below 700 MHz) it always works.
Firmware version is 01.15.90 and installed options are 300 Hz RBW filter, phase lock, tracking generator, centronics and frequency counter.
When the fault kicks in there's something going wrong with center frequency control. Frequency domain of the spectrum is shifted about 26 MHz lower, for example is center frequency of 1.2 GHz is set and that signal is fed to the analyzer the peak will be found at 1174 MHz. Some times it may "jump" between correct and wrong frequencies when the center frequency knob is turned. Amplitude is measured correctly.
When changing to narrow spans (20 kHz/div or less) and the phase lock option is turned on it will sometimes even lock to the wrong frequency! When this happen the frequency counter option (which can be used to count any displayed peak's exact frequency) will also show about 26 MHz wrong.
However it's quite common situation that when the frequency domain fails the phase lock and frequency counter options won't work anymore. Error message "FREQ NORM SUGGESTED (1ST LO)" or "FREQ NORM SUGGESTED (FIND SIDE)" is displayed instead. Of course running that normalization process does not help and the normalization process will be passed without any errors.
This unit has YIG local oscillator. I have service manual and I'm already done the reference normalizations, span attenuator and center frequency accuracy adjustments, LFVCO and HFVCO adjustments and counter level adjustments to fix the fault - no help. Service manual won't help with those error messages for example what's the "FIND SIDE" is meaning?
The center frequency control system is quite complex (it's 80's technology) and infact there's 26 MHz VCO on center frequency board, which controls the YIG's coil currents/center frequency. This could somehow explain the 26 MHz frequency error but how - and why this problem only happens on higher frequencies?