Broken Scope Update: Transistor testing? Replace blown ones with commonly available equivalents? or BER? Answered
So in a previous question, https://www.instructables.com/answers/My-oscilloscope-died-How/ I have stated that my oscilloscope died, and listed the symptoms. Since then, I have popped the cover off, had a look inside, and was I found inside what certainly appears like a "mod," it goes off to the 3 by 3 connector I have mentioned also. I forgot to mention a small blueish purplish wire was next to it, similarly just sticking out the scope. I figure it is a MOD because it is:
A) precariously mounted to the transformer with only one small nut on the transformer
B) Has so many bodge wires crawling around on it, that it looks more like a cobweb (and w/o silastic or hot glue for vibrations/stress)
C) Sloppy soldering and flux residue left behind indicating hand soldering
D) The PCB has a very different appearance than the rest of the boards inside; No solder mask, greyish white, and no silkscreened values, parts, or numbers.
I traced both the wire and the connector and ribbon cable to the same mod board, which clearly got toasted. There was a small orange wire tangling off that board, it it broke off before I even realised it. Luckily the pictures show roughly where it was connected. Tracing the blue wire back to the board, I discovered it is connected directly to one of the cooked resistors, and I think the other cooked one was in series with it.
The only connection found to the main board is the orange wire, and there are ceramic capacitors in series on that crappy looking PCB, indicating it is capacitively coupled. I was Hoping that what had happened was the blue wire came into contact something it was not supposed to, and shorted the output of that chip causing it to catastrophically fail, knocking out power to some of the boards. Unfortunately did not appear to the the case, and the supply voltages seem OK.
Nothing appears obviously burned out on any of the other boards from what I can tell. However, just today I have discovered that some driver transistors, which are mounted to heat sinks, are getting unconfortably hot to touch. I suspect they may be blown, by the blackening and discoloration around them on the PCB.They themselfs do not appear to have any physical damage. I will desolder them and connect them to a transistor tester I have to see if they register as operational.
As for some additional questions, can I replace those weird looking obscure transistors with standard ones? I am not sure of their exact specs, the only datasheets I can find for "2SA818" and "2SC1628" are some scanned PDF datasheets that are not in english, and I certainly could not find replacements online for them. I have the gut feeling radioshack is not going to carry them either. :P
I hope this is not Beyond Economical Repair (BER), but used analog scopes can be bought used for around $30-$70, and of course I am on the verge of getting something better than that.