Hello, from viewing your video I would suggest that there a number of component parasitics which possibly are causing adverse effects of the operation of the PLL. I note that you are using IC sockets and that would cause additional capacitive loading (and extra inductance) on the Motorola PLL IC. My suggestion is to avoid the use of the IC sockets. Solder the IC direct to the copper pads of the PCB. The PLL PCBs need to be super clean - so my suggestion is to immerse the boards in IPA and agitate the surfaces with an unused clean stiff paint brush, till all traces of the hardened flux residue are removed. Stubborn flux residue may be pricked with a small sharp tool to start the process. It was very common in the 1990s not to remove flux during manufacture. Flux however adds additional parasitic capacitance to the pins of the board. To remove the flux, use a bath of IPA solution in a container. Do not use nail remover (acetone) as this will soften the plastic mouldings and have an adverse effect on switches, coil formers, plastic fixings, adhesives and such like. After the pcbs are cleaned, blow dry using a compressed airline or spraycan. Perform a visual inspection under a microscope of all solder joints for more flux and dry solder joints - high impedance points. Resolve as necessary. The VCO cans will also need to be removed so that the IPA can make its way in the enclosure and the flux residue can easily flow out. If you have difficulty in removing the VCO cans, you could also use an aerosol type spray of IPA to drive the hardened flux out but this may not give a consistent fix. Careful use of a hotplate or hot air gun will help. (You may need some practice though.) When resoldering the cans, it would be necessary to clean off the flux residue as well. Whilst the boards are soaking in the IPA, spend a few minutes cleaning up the mounting pillars of the main enclosures ensuring that the mounting faces are clean of flux residue and finger grease. All surrounding metalwork should be bright and clean. Use metal polish if you wish but degrease the metalwork with IPA afterwards. Before reassembly , check the components of the PLL boards for abnormal swelling of the capacitors and inconsistencies. Check and renew any board mounted batteries. When reassembling the PLL boards (actually any high gain pcb), avoid skin finger contact with the mechanical screw down pads or any of the components as this may transfer the finger grease. Check that the undersides of the screws and washers are also clean of paint and flux. When tightening down the screws of the PCB, use sufficient torque (not excessive!) to ensure that the resistance of the bond between the pcb copper and the mounting pillar is no greater than 25 milliohms. (Use a 4 wire milliohmeter for this.) Further perform a pcb to pcb ground check and confirm that the bond resistance is of the same order. Also do this check for the pcb to metal work for the enclosure and then for the pcb return to the power supply negative. If you find this to be excessively high then you could substitute a ground strap in. However, be careful not to induce an earth loop causing more issues. Ensure that all the interconnecting cables forms are held down as close as possible to the vertical walls or horizontal floors of the radio. Use nylon tie wraps. Finally check and confirm that all the sheet metal work is clean and is screwed down correctly. This is to avoid high impedance paths for the return currents. Good luck in this worthwhile exercise. Please do be aware that your experiences may be different to mine.

Check the details voltage to the vco and is within range. If not you can cheat by increasing the dc voltage to the vco by lifting g the ground lead on the voltage regulator and fit a diode between the the ground lead and the ground connection. Thus increases the vco voltage range and might help lock the vco. Also check the decoupling capacitors in and around the vco circuit as this will destabilise the vco locking.