The main board can have only vertical hold regulation or vertical and horizontal hold potentiometers. In case there is only vertical hold regulator, the vertical hold potentiometer is missing, its terminals are shorted on the board and on SG module pin 1 is connected to pin 3. Such board also does not have pin 3 installed on the SG slot.
This is a power supply from 1981:
This is a power supply from 1985:
The photos of the modules are of the two manufactured versions: one from 1981 and another from 1985. Their design is no different between these years.
NF Module (X1301)
Probably this is a Negative Feedback audio power amplifier module.
SG Module (X1501)
Probably this is a Synchronisation Generator Module (Synchrogenerator Modul).
VAD Module (X1401)
Probably this is a Video-Audio Decoder module (Video-Audio-Decoder Modul).
VK Module (X1601)
Probably a Video Control Module (Video Kontrol Modul) – the three potentiometers are for regulating vertical linearity and size.
Intermediate Frequency Module (Zwischenfrequenz Modul)
RF Tuner Module
Composite Video Modification
My TV came with a mod that added composite video and audio inputs to it. The original mod looked pretty messy:
It adds 2xRCA inputs, a switch to choose between RF and AV and a potentiometer to regulate the input signal brightness. I took the modification apart and put it back:
Here is a reverse-engineered instruction how to make the modification: