Here we have a Marconi 2966A radio communicaitons test set, with AM, FM, Phase Mod & SSB Gen & Demod capability from 100KHZ to 1.05GHZ coverage. This came with a description of not working!, no other info, upon testing we find multiple faults, we also in the course of this video find evidence someone else has had a go at repairing this test set before me, infact they have caused a number of faults by damaging cables, circuit boards, connectors, plugs & sockets & Keyboard. We put these right only to find we go on a wild ride of our life time when we realise the TX Power doesnt read properly, & the FM TX DEMOD Modulation measurement is way out of spec & does not autorange, whilst the AM is reading correct, the RF Sig gen & Spectrum analyser shows incorrect levels & we embark on extensice factory level calibrations, resets & fault finding to component level. We start to swap boards from a known good service spare 2966A, in order to establish the suspect PCB once we prove the issue isnt related to the RF tray, we look at the i2c data bus & establish the x10 AE7 AF attenuators are being switched for the TX FM demod auto ranging bar chart & Scope readout for this RF demod measurement which points towards DSP & FFT issues. Reading the 1500 page service manual & carrying out adjustments as per instrucitons we eventually trace the FM demod issue to the Microprocessor board which shares its DEMOD measurements with the Diplay board FFT processor. we prove this by swapping it with a known good MCPU board from another 2966A to find the instrumnet now works correctly. We resolder the original MCPU PCB & its chips, sockets, & test supply lines, checked PCB fuses FS1 & 2, & microscope inspection of MCPU PCB on both sides to find no issue. we finnaly reset all parameters in the Factory calibration menu & load in the default manufacturer info. We complete all calibraitons one by one & restart the test set, we finnaly realise this has not resolved the issue, & we stop the repair due to cost & unavilability or replacment MCPU pcb. knowing where the fault is provides some reward as many hours spent trying to pinpoint the issue but you cant win them all, we are defeated, the situation was not helped by the fact somone else has been inside before me & i am sure this person had damaged the instrument MCPU pcb to such an extent it would be uneconomical to continue. What a shame, i was really looking forward to getting it fully repaired. but in the end its 99% done with only the TX FM demod issue outstanding.
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Marconi 2966A RF Radio Tester Repair, covers Marconi 2965, 2967, 2968 models, Multiple Faults.
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