вот описание работы всего узла

It is esentially an inverter circuit. TR5, TR4 and the coil forms the inverter. It generates a pulsating 12V signal at the collector pin of TR4 (it comes from the reactance discharging through transistor TR4). That signal is AC coupled by C80, so we have something similar to a 12V AC power supply, of about 110kHz, at the right side of C80.

D15, D17 and C44 form a simple rectifier and a simple filter. As frequency is much higher than 50Hz, no full rectifier or big capacitors are needed in order to have a steady power supply. The junction at D15 and C44 carries a 12V DC signal suitable for DRAM chips.

The same voltage is passed through a PI filter formed by C44, R62 and C45 to give another 12V supply rail, isolated from the first one. This isolation (achieved in some way because of the PI filter) is needed to avoid high frequency switching noise coming from DRAM chips to enter the video circuit section, which would make it to display on screen, degrading picture quality.

To generate -5V, a similar circuit is used: from the same point the 12V supply is got, another capacitor, C46, gives a 12V AC signal. Diodes D11, D18 and capacitor C79 play a similar role to D15, D17 and C44. Only that this time, diodes are arranged in the opposite direction, so the output signal is negative (with respect to ground). D19 is a 5.1 zener diode, which is used to lower the voltage from -12V to -5V. In order to not to destroy the zener, a current limiting resistor R79 is used. The -5V supply is very weak and only used to polarize the substrate of DRAM chips.