Hi,
Not sure whether this should be here or in the test-gear forum...
I've got an old Crotech 3132 20MHz scope that stopped working yesterday. After having it switched on for a couple of hours, it's released an acrid burning smell and isn't producing a trace on screen. I've taken the covers off and think that I've diagnosed that there's a fault on the EHT board (see page 4 of the attached diagram):
http://www.tjstephens.com/images/Crotech3132 _circuits(wm).pdfObservations:I've got the circuit diagram for the board after trawling the web, and I think that the board consists of an oscillator (a Wien oscillator?) and a two-stage (Cockroft-Walton ?) voltage multiplier. That's where my understanding kind-of ends.
The NPN transistor Q601 is on a heatsink and was very hot when I first checked it after unplugging the scope (and making sure that the various caps on this board were discharged).
The two resistors (R613, R614) on the output stage of the transformer have clearly been very hot. Their paint is peeling and the surfaces are charred, although they measure 5.8K and 6.1K, so they're still performing at about specification.
Can you suggest where I might look next? I'm not sure how to confirm whether these observations are a symptom or the actual fault (my guess is that something else may have failed upstream)? Is there anything else that I should be looking for?