Repair of a Collins 651S-1 receiver. The 65-95 mhz vco module is bad, but if you over damp the pll loop filter it does eventually lock and receive properly. I found a similar but not identical replacement from a different model receiver. It lacks one of the two DC tracking signal outputs but I added an op amp based circuit to simulate the missing signal.

The loop is stable and responsive when receiving from 17 to 29.9999 Mhz, but not much below that... Almost got it