Apple Multiple Scan 15AV CRT monitor repair

[tony359]

Update.

I swapped the transistor and checked things around.

The monitor powered up and stayed in standby happily (Yay!). When I applied VGA signal, the monitor fully powered up, I had HV, a weird image on screen and then The Magic Smoke!

The same transistor shorted (Base with Collector) and a resistor connected to it went on fire.

I've looked around and here are my notes:

- The transistor seems to be generating +70V for the neckboard. On the Neckboard there is a CVA2422TL CRT driver. I've noticed that I've got 90Ohm between GND and the 70V line on the neckboard - my other neckboard reads some Kiloohms and climbing.

CVA2422TL datasheet: https://pdf1.alldatasheet.com/datash...CVA2422TL.html

Shall I move my attention to the neckboard? Could it be the reason why the 70V rail fails every time?

Could a bad CRT cause this issue on the neckboard? Please note I read 90 Ohm with the neckboard disconnected from everything (but the Flyback)

I don't want to give up know. The area which went up in smoke seems pretty simple - I'm sure some of you can recognise the topology, I suspect it's some voltage regulation?

When the screen came up it was pretty weird, white with blotches. Maybe someone can recognise the symptom of something? See video below.

Also, I cannot assume that the trimmers around the PCBs haven't been touched. Still, I wouldn't expect components to go up in flame if something is misadjusted?

Here is the video of the accident (I have a small youtube channel where I publish my repairs):

https://www.youtube.com/watch?v=YqpgZc0HX2M

Attached some pictures - the main PCB is single layer so the circuit can be easily followed there!

Thanks so far!