[Red to black]

The reason I said look at the TX100 manual circuit description for this Psu was because this chassis was the first that used the novel scr fast Thorn start up version of this circuit.
The later TX99, 98 also used it but their manuals already assumed that Dealers were familiar with it by then, and so didn't need such a comprehensive introduction to it in the later manuals, the earlier MK3 TDA4600 TX9 chopper version never used it, the TX100 was the first,

Ps. the TX98 posistor was also used as the surge limiter resistor too (a first for Thorn) similar in operation to some versions of the Philips 2A chassis and all of the later Philips CP110 chassis