Re: My first foray into Old model TV repairs.
The switch off spot is quite normal, nothing to worry about.
The tuning cores break away from the threaded brass rods connected to the tuning plate that carries the tuning control. All visually looks OK but the cores are usually stuck in the coils and will require pushing out through the bottom of the chassis with a thin tool once you have eased out the spring metal clips that have the brass adjusters threaded through.
I have built some new tuning cores with some radio types but the threaded rods are a bit short. I have cut one of the brass threads off one core and super glued it to another threaded core. They are spot on. I can let you have some spares if you need them FOC.
A tuning tool can be made from a cheap screwdriver and a hacksaw.
The 991T is very high gain and when working correctly it should be possible to obtain complete white out overload with the gain and contrast controls advanced.
The pictures show: Attenuator in aerial input 12DB. Attenuator 30db and aerial direct with gain and contrast advanced. Complete overload with direct aerial connection with controls advanced. Remade tuning cores and modified cheap screwdriver for tuning and finally the switch off spot.
All the caps in the frame stage will be shot. The linearity should be 100% with plenty of free adjustment.
Incidentally I had to realign my I.F. strip to the makers data. It had been aligned for maximum gain. It must have struggled with a very weak signal.
John.
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