IT may not be a bad idea to "track" the LSB and USB votlages BEFORE they get to IF mixing. If the jump occurs and it's DC is steady, then rule out power rails - but if intermittent - that means parts that are loose or bad routing or mounting.
I have dealt with SEVERAL SMD radios that got "epoxied" (sprayed) sealed from the factory only to see soldering "balls" and poor - cold joints in certain areas - again - looking for fresh work. It's a good clue as to what they were looking at before they sent it out.
The "dip" process is not as foolproof as many would think - the parts do fall off, and "cold spots" form when a board is "touched" by humans to re-align it from shifting or a simple flux wipe didn't cover the board well enough due to air pockets.
So I would not put it past them if several balls were laying inside the coils cans or on the main PCB to cause these jumps. OR the SMD caps for trimming were loose or pooly soldered into their "cubby" on the coil form.
Even the Epoxy can migrate causing issues - you've been dealing with it since day one...
Hope this helps!
:+> Andy <+:
I have dealt with SEVERAL SMD radios that got "epoxied" (sprayed) sealed from the factory only to see soldering "balls" and poor - cold joints in certain areas - again - looking for fresh work. It's a good clue as to what they were looking at before they sent it out.
The "dip" process is not as foolproof as many would think - the parts do fall off, and "cold spots" form when a board is "touched" by humans to re-align it from shifting or a simple flux wipe didn't cover the board well enough due to air pockets.
So I would not put it past them if several balls were laying inside the coils cans or on the main PCB to cause these jumps. OR the SMD caps for trimming were loose or pooly soldered into their "cubby" on the coil form.
Even the Epoxy can migrate causing issues - you've been dealing with it since day one...
Hope this helps!
:+> Andy <+: