PSU and Modulator Issues
The SAM power supply housing contains two circuit boards, one is the actual power supply board and the other is the RF modulator board.
The cable to the SAM has 6 wires, some of them terminate on the power supply board and some on the the modulator board.
From the power supply board red (+ 5V) and black wire (ground) cable go to the modulator board to power it, these then connect via the DIN plug to the SAM using the yellow (+ 5V) and white (ground) wires.
Warning: SAM's have been found in the wild with different coloured wiring so please make sure you check with a continuity meter that the below assignments match!
The assignment of the on-board SAM DIN connector (rear view) :
1: +5 V yellow
2: 0 V signal white (connects to 5V ground on modulator board)
3: 0 V digital black (connects to 12V ground on power board)
4: Comp. Video red
5: + 12 V purple
6: Mono Audio Out blue
See attached schematic PDF (in German) from Search: “Dieter Hucke” originally from http://www.8bit-wiki.de/index.php?id=3&filt=MGT_Sam-Coupe/diagram/&cid=15472&mode=dl&tx=adb32890000 [defunct]
Replacing the 12V Diodes and resistor is highly recommended, see Hardware Bugs and External PSU Modification.
There are two large 4700uF capacitors for smoothing the 5V and a 1000uF for the 12V, these are also recommended for replacement due to the load and heat factors inside the PSU case.
The two 5V regulators may need replacing (and uprating to 1.5A L7805CV units) especially if you find they have been left unattached to the heatsink shield.
A common failure point is the RF modulator, especially with the sound output, new-old stock replacements can be found, see the Replacement Parts List but again using an RGB SCART is always recommended.