Been trying to repair the 2235 got at an auction. Repaired a number of these many, many years ago when a bench tech in metrology dep't. Most had power supply issues.
This scope brings back the aargh I got back at that time only worse. Some parts can no longer be found. Found Sphere sold the last C906 in stock. Allied is a good source for semiconductors.
Allied Electronics But back to this scope. I replaced R926, the 150k resistors that C925 charges through. Strange thing is that when I measure the replacement resistor it seems to discharge through the meter even before the scope is turned on. Measure in the meg ohms then after a few minutess settles in around 150k.
Found the 6.2 v zeners. out of tolerence or even open. The mosfet IRF710 has blown several times. Replaced Q930, 928, the 51 v zener in the crow bar and scr. Finally got the power led and the uncal'd leds to blink as if the 5 vdc as trying to turn on. Seems like it's trying to operate. Disconnected the links from the all the power supplies. They blink once about every 2 seconds.
Q928 sms8512 is not readily available. Subst. 2n2222, 3407, 4401 made no difference. Removed some of the caps. Ran them up to just under the breakdown voltages with an ammeter in series and found none with any leakage I'd be concerned about. Then measured them on a capacitance meter where they checked ok. What else can I do without putting the scope under the wheels of my truck.
Errors on the board include Q928 which is marked as Q944. The spot where Q944 really is is not marked at all. The serial # is B70418 option 1 and is the AN/ASM 448 mil version. Have the repair manual for the civilian model and found the mil version in pdf format. Both have the same errors.