Breaking and now trying to fix a sad Tektronix 2245 Oscilloscope

[Ferrix97]

Hi!

I recently paid another visit to the same recycling center where I scored the Keithley 2000. This time I found a Tek 2245 scope in a very sad shape: both front and back plastic covers have cracks in them, the metal chassis is all dented and to top it off one of the knobs (holdoff) is missing. It was also covered with a fine white powder.

When I got home I plugged it in and it started working: all four traces and readouts were present on the screen. I din't try feeding a signal into it.
Seeing it working I decided to take it apart to better remove all that white powder off of it. Upon opening it, the chassis snagged on Q702 heatsink's and partially pulled out one of it's legs... Doh!
At first I didn't notice the damage, but when I turned the scope back on, the display was "shifted" up: the readouts on the bottom were in the middle of the display.

Reading online this seems to be quite a common issue: https://bradthx.blogspot.com/2014/01/how-i-accidentally-destroyed-my.html

Upon desoldering and measuring it out of circuit, it became clear that one of the legs wasn't making contact with the silicon die inside, so having nothing to loose, I carefully cut it open and noticed that one of the bond wires was disconnected. I fixed that and soldered the can back on.

Soldered back the transistor to the board and turned it on: it worked again! I then reinstalled the heatsinks and powered it up again. This time around the screen was shifted again, but the other way around! now the trace would sit in the middle with the position set to the top.

Measuring the transistor again results in a collector-emitter short...

Does anybody happen to have a spare transistor lying around? In the meantime I'll get a 2N3866 to see how it behaves. The main difference between the two is that the base is tied to the case on the original 151-0846-00 part, while on the 2N3866 the case should be tied to the emitter. The pinout between the two is also different (it should be "flipped").
To alleviate that I was thinking about covering the case in thin kapton and then soldering a wire from the base to the heatsink. Is that a good idea?

Thanks!

[Ferrix97]

Fixed!

The 2N3866 works perfectly as a 151-0846-00 replacement. They just have a different pinout (https://groups.io/g/TekScopes/topic/7658065?p=,,,20,0,0,0::,,,0,0,0,7658065)

2n3866A
..B..
E...C
^


151-0846
..E..
C...B
^

[Terry01]

Nice fix! I hope it lasts and that you get the rest of it fixed up ok. Pretty cool!