VHF90's and me!

[Yorkie]

Are the bulbs ok - have you tested them Rob? (The set will work just as well without them as there's a shunt resistor in parallel with the bulbs).

If the valves are alight that means that the heater chain is intact.

If there is no glow from the lamp limiter that's a good sign.

Have you checked the HT or any other voltages per the circuit diagram? As I said earlier, the excellent 10-page Bush circuit has several key points at which the voltages are stated. If the voltages are low (as they will be to an extent with the lamp limiter in series), as the lamp isn't glowing, it should be safe to switch the lamp out of circuit so that the full mains voltage is applied to the set.

You can check if the audio stage is working by applying your signal probe to the centre pin of the volume control to see if you get a tone at the speaker. If not, there is a problem in the audio stage. Using your RF probe apply it to the centre pin of the volume control and see if you get any tunable stations on any bands. If yes on AM but not FM, problem in the FM tuner stage. If no signals, can you substitute the valves with a working VHF90 to see if the valves are all OK? EG, if the frequency changer valve (mixer/oscillator), even if the IF and audio stages are fine, you won't get any signals.

You can work your way to the front end of the set with the signal tracer RF probe to see if you have any sigs at the IF stages output and input.

You can check if the oscillator stage is working by putting another (working) set alongside the one you're working on, and if you 'rock' the tuning of the set under test either side of the same point on the dial, you should hear the oscillator beating with that in the good set.

Just a few pointers which might help Rob.