Unfortunately delays on this - a display for one of the radar systems needs urgent repairs!

The main 24 volt DC input regulator is working - 24v DC input and a regulated 24v out with all LEDs on showing Aok

But the unit is basically 'dead' - checks reveal that the main system power supply unit had failed :(

IC 1 SG3524 (PWM powercontrol circuit) and IC2 TL111 (optocoupler) had both blown - none were socketed so dud chips carefully removed and IC sockets put in to assist any further servicing needs in the future should these chips blow anytime again!

Unfortunately there's no servicing manual for this unit anymore, so it's a step-by-step process to get it working again. Currently replacing the two IC's I've managed now to get all supply lines reactivated again - and the front controls and display digits power up - but nothing on the CRT...

In operation however zener (D3) is getting VERY hot, so something is causing a very high current, way over what is should be!

Maybe that's what blew the Pulse-Width Modulator chip? Not sure, as the chip has onboard current limiting and shutdown circuitry, but more work needed......