This is an SG613 set, actually SG264 that IIRC subs to an SG613.
If the SG is shorted I would STRONGLY suggest not trying to fix it.
The regulator transistor & fuse are blown with it along with a few resistors.
Trouble is something else caused it almost always. If you dont find the cause
it will blow again right away or sometimes run perfect a while then blow.
In the day almost no shop would fix one. The ones that did charged flat rate $120 - $140 about double the usual rate. That was real $$ back then, see the price of cars !
73 Zeno
LFOD !