[Radio Wrangler]

It's quite a common issue with PLLs in amateur radio rigs. Many people assume that if the right frequency comes out, then all must be OK.

In reality this gives you no information about whether the adjustments are still good and that the loop is in lock with decent margins. It could be close to dropping out.

Every several years, it's worth sticking a voltmeter (high Z) or scope on the tuning line of each loop and spinning the tuning across its range to check the voltage is within the correct limits. It's an excellent health check, and no other test reliably tells you how safe their lock is.

David