Steve. My very limited involvement in circuit board soldering failure/dry joints suggests you check carefully where *thermally massive* components are attached.
Assembly may well have moved along from the *solder bath* technique where a wave of molten solder washes over the back of the assembled board, but, localised *chilling* can lead to poor quality connections.
I once bought an ex rental colour tv that required percussive maintenance to get the colour back
I discovered instead of through hole plating, it had some form of pop rivet connecting tracks on either side of the board. I soldered every single one. Both sides...took me a whole afternoon.
The TV was rock solid for years until it got destroyed by a direct lightning strike on the house phone line.
It wasn't worth repairing...
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