I have repaired a few dozen of AS-2518-16, AS-2518-22, SDU-100 boards.
Most of them I fixed with ease.
Now I have two boards which got me puzzled.
The 5V section is no problem, fairly simple the fix.
The solenoid driver section also no problem.
The High Voltage section is a bit harder.
When this section is broken it is very easy to notice the burned R51 (22K) resistor.
I replace the 2N3440 transistors and the expencive 2N3584 gets replaced with a BUX85G transistor.
When all the transistors are off the board, I check the diodes and the resistors for correct value.
Check the potmeter for correct working order and replace when nessesary.
On the two problem boards I can't get the voltage regulated.
It will stay at a low 100V and does not change when adjusted via the potmeter.
It looks like the 140V zener diode is working correctly (240V-140V=100V output).
Can someone send me in the correct direction to search for the broken/incorrect part?
Can someone explain exactly how this high voltage regulating section works?