My 89441A Vector Signal Analyzer has stopped working with its 89431A RF section, with an error message saying the reference oscillator is unlocked.? I have confirmed that there is no signal coming from the 89431A reference oscillator output that feeds the IF section.? The fault appears to be with the local oscillator (LO), and investigation shows a red overcurrent LED on the +8V supply with the voltage at the test point measuring about 4.8V.? Module A64 in the LO is drawing quite a bit of current, about 1 amp.? With the A64 module disconnected from the +8V supply there is a 10 MHz signal present at the reference oscillator output of the 89431A, although the overcurrent LED is still lit - the voltage reads about 7.5 V.? There could be multiple faults or perhaps a problem with the overcurrent detection circuit.
The A64 module is an amplifier containing two 1GG3-4205 devices, and each of them draws about the same amount of current.? I have been unable to find any information about this device and CLIP level diagrams are not available for the 89441A system from what I've found.? The 1GG3-4205 device now appears to be unobtainable.
Does anyone know if the 1GG3-4205 is supposed to draw about 500 mA?? If not, can anyone recommend a suitable substitution or workaround (I've read that someone has successfully substituted a Mini Circuits module on a different piece of equipment but which one isn't stated).? If it is normal for these devices to draw so heavily then it is possible that the overcurrent detection circuit in the power supply has a problem.? Without component level information all I have is HP house numbers and endless guesses as to what is actually going on.
Any suggestions would be appreciated - I just don't have enough information at this point to make any headway.? Thanks for reading :)
