Hi

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?

--
Esa
http://www.amigazone.fi/contact/english