[G0HZU_JMR]

I can dig out my TR4172 and try a few tests but I don't think my analyser IF1>IF2 block is the same as yours. I think both of my TR4172 analysers are the same as each other with similar serial numbers but I don't think they have the same 206MHz BPF technology as shown in the service manual. I assume mine is newer (but it could be the other way around).

When I had the original IF1 failure mode I did trace the signal path from the input to the 3.3MHz IF output at the back of the RF unit. Looking at the old internal images of my analyser the 206MHz filters are vertical with top adjuster screws. The filter cans stick out through the main lid, i.e. the RF block lid has square holes in it to allow these filter cans to poke out. In other words, my filters can be adjusted without removing the metal covers of the RF/IF block. I'm not sure my analyser has the two switched 30MHz BPFs at the 3rd IF either. It looks like the signal path of my analyser is quite different here.