[R-390] R-390 IF Deck

[Jim Whartenby]

Where is S504?  I see S501, S502 and S503 but no S504 in the schematic or parts list.
I personally think that the 8kc mechanical filter now has a high insertion loss due to the internal "rubber" isolator turning into goo or perhaps a weld connecting a wire to a disk has failed.  I have seen both.  If one has any mechanical skill and patients, the filter can be repaired by careful disassembly and replacing the "rubber" isolator.  If it is a broken weld, the filter is toast.  The filter repair info is in the Pearls of Wisdom, IIRC.Regards,Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy 

    On Sunday, January 12, 2025 at 11:20:20 AM CST, Jacques Fortin <jacques.f at videotron.ca> wrote:   

 Hi Jerry,
Yes: we do not know what happened before with these old modules...
A bad previous repair or a defective S504 contact can be involved.
A full check is in order, IMHO.

73, Jacques, VE2JFE in Montreal

Maybe something as simple as a cold solder joint on the switch?
Jerry NY2KW

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