Grundig music boy universal 206 local osc problem

[Goldieoldie]

Hi
The radio works ok on vhf except below about 92 m/cls it stops oscillating
I have changed the af125 and sub most of the components incl the v/c ( no it's not shorting )
I have tried other transistors with the same result
It calibrates ok just won't oscillate below 92 megs !
When I tune it at 92 m/cls with a scope attached it's like a switch going on/ off
Not graduly decreasing in amplitude
Has any body with experience of these radios had this fault !
Circuit attached of osc section
Cheers Pete

[JohnBHanson]

I have seen this before but with a different circuit. Turned out to be low gain on the feedback to the oscillator caused by a low power supply to the oscillator circuit.

As the radio calibrates correctly it is not likely to be the caps or inductors in the circuit. Check that the voltages on the transistor pins match what is on the circuit diagram and how these voltages are derived.

[Goldieoldie]

There is about 7 v between the c and e
Bias seems ok too

[JohnBHanson]

Also check the base de-coupling caps. Try adding another cap in parallel with each as a quick test.

If any of these are oc it can result in a loss of gain. Around the osc circuit this could well have the same effect.

[Leon Crampin]

Check for a bent plate in the tuning capacitor - osc section.

Leon.

[Leon Crampin]

Just realised what "vc" refers to. Best not to use undefined abbreviations unless standard. A check on supplies, bias (check the bias diode carefully) and decouping is next.

Leon.

[Goldieoldie]

I have added some de couplings caps to the base ,still the same
The bias is fed from a 1.4 v source which is correct
I'm stumped !