National TC333G

[60 oldjohn]

This 14inch portable CTV is suffering low gain, like no or a very short aerial. Also the same with a STB. I do not have a circuit for it. Was there a stock fault? I have not removed the back yet. The picture is watcable, but far from right. The coax socket on rear seems firm. John.

[tiv48]

is this the one with a mechanical tuner? if so take the side off clean and regrease check the tension of the leaf springs where they contact the rotor and check the first rf transisistor. could be a fault in the earlie if stage or the agc line. ps whats on the screen with no aerial pluged in?
rob t

[60 oldjohn]

Hi Rob, Thanks for helping. Strange results, There are no less than 14 controls available through rear without taking back off, not including the normal vol col bright con ect.

Aerial disconected BBC1 BBC2 IT, B&W with snow not watchable. C4 in colour just watchable. Channel 5 always weak nothing.

With aerial. AGC seamed to be at max when I alterd it possibly slightly improving 1 2 itv1 not much different on 4, but nothing on C5 until I removed aerial then fait C5!

The tuner has 8 buttons with preset for each and AFC swich.

The set is 240v and 12v.

Thanks John.

[tiv48]

ah a later varacap tuner!can you find the agc pin? if so conect an external voltage source of between 0 and 9 volts if no or small inprovment at any volts tuner is suspect.take off sides and check for solder dry jonts ect, some of thease tuer came back to life by simply removing the sides.
rob t

[Electrical]

Hello John
Please find attached a PDF copy of the service information for your National TC333G, from the 1978-79 volume of Radio and Television Servicing. The fault sounds like there is a fault with the RF amplifier in the tuner, but there is a vision IF preamp TR101 between the tuner and the IF amp IC101. It may be worthwhile checking the voltages around TR101 first to see if is amplifying and the voltages on the tuner and the AGC line to the tuner and at IC101.
Regards Stan.

[60 oldjohn]

Thank you Rob and Stan, I have the R&TV servicing but missing that one, so thank you very much very welcome. I cleaned the service swich and AGC pot picture may be slightly better. I will be back when I get time. John.