Marconi 2022 10KHz - 1GHz Signal generator attempted repair OM345 RF Hybrid issues low RF output.

Here we embark on a repair of a Marconi Instruments 2022 RF Signal Generator boasting a frequency range of 10KHz to 1GHz FM, AM & Phase mod, we firstly look at the history of Marconi instruments, & look at the production environment where the signal generator was made, we look at the spec & technical info then porogress onto confirming the fault using a HP Agilent spectrum analyser, We also find that not only is the RF level way out of specification being of a very low level when compared to where it should be & we also establish the RF ALC circuit is not allowing 1db increments of the RF level or (fine adjustment of the RF level) We also find the signal generator is unable to produce a signal below 17MHz & thus three faults exist. We then look at the theory of operation & learn how the instrument circuits work in the functional description & examine the signal path in the circuit diagram exploring the different modules & VCO circuits & associated amplifiers. We measure RF signal levels to the hybrid high gain amplifiers & fault find to component level using an HP Agilent 8920 radio test set with receiver. Having found a defective OM345 RF hybrid IC we need to find parts & look at spares sourcing remembering this product is 40years old.