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N5181a A3 unit

Question asked by Integrator on Apr 2, 2017
Latest reply on Dec 12, 2017 by jonathan.falco

Dear support team,


I have N5181A with problems on A3 unit. Once I have faced with Open loop and VCO test error. I spent hours in troubleshooting and checking, drawing on circuit diagram of VCO A3 unit (attached). I have found that if I remove resistor 4221 the VCO syntezer  test successfully passed. But phase control loop test (next one) of corse not. 

To be honest I do not completely understand how this part works and, as a result I can not find the root case of fault.

Could you help me with understanding or give me some advices about repair?