Hello, after some weeks of inactivity our HP8703B network analyser got a serious failure.
It shows a warning like: Phase lock cal failed.
As the equipment has get obsolete it seems impossible to repair it, so i will try that here at our university department.
I measured the output in CW with an oscilloscope and one dominant frequency around 2GHz appears.
with an spectrum analyser it can be seen the contributions of other several frequencies like about:
CW= 200MHz --> the output has= 950MHz, 1.46MHz, 1.5MHz, 2.2G, 2.4GHz contribuitions
CW= 1GHz --> the output = 990MHz, 1.45MHz, 2.4G, 3.8GHz and other small contributions
CW= 2GHz --> the output = 950MHz, 1.46MHz, 1.5MHz, 2.2G, 2.4G, 4.7GHz,..
CW= 9GHz --> the output is dominated by a 7.18GHz component
I have no idea which the problem could be, perhaps the controller ?, the oscillator or the reference parameters?
Unfortunatelly I have only the user manual and did not found a service manual for that HP8703B, to check.
but I have seen one post about a similar problem with a HP8753 NA which gives some hope to recover the NA.
I would appreciate very much any recommendation to fix the problem and to find a similar service manual.
Performing the calibration tests of the NA I measured the waveform of the 0.5V/GHz signal to the YIG oscilator. The test showed problems with the controller waveform (attached file, expected = black curve, measured= red curve). According to the test manual, this stands for "Broadband Phase Lock Problems". Following the next tests to isolate the failure, it was noticed a hardware problem in the controller card: the card began smelling because a component was getting heated too much, probably related to the phase lock fail ?
I wonder if is it possible to find any cause-effect relation between the failures?
I will appreciate any help,
By checking the hardware it was concluded that controller card is ok, the smelling was from a capacitor in the power supply.
From new tests regarding the phase lock fail :
-Microwave source pretune correction constants test (43) passed (ok)
-VCO tune adjustment test passed (ok) at A12 reference assembly.
at A12 reference assembly, Frequency accuracy adjustment (VCXO) NOT PASSED, the >14GHz expected tone was not continuously present, sometimes a 7GHz tone appears while sometime appears the expected 14GHz, and potentiometer adjust does changes anything --> Manual recommends replacing the A12 reference assembly.
-Source oscillators test NOT PASSED, neither Dac Num HIGH, MEDIUM nor LOW band. It is expected -3dBm but No power appears, while DW10 connector voltages (Microwave test set bias voltage) are correct. Manual claims for A51 is faulty.
-the 0.5V/GHz signal for the YIG oscillator driving was measured again: figure one is the expected to pass the test, and figure 2 and 3 are two measures, both not passing the test. The measurement varies with the sweep, so faulty is strongly related with that waveform generator?.
So with the NOT PASSED TESTs, two faulty lines are open, but as the system seems working in the range from 8 to 12GHz when the 0.5V/GHz waveform signal driving the YIG oscillator is active, and it is difficult the three oscillators to fail together. I could consider the faulty is in A12 reference assembly. Is there any A12 internal part to be the candidate for that fail and which can be replaced ? Which particular component into the 0.5V/GHz waveform generation part can be involved in that faulty?