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Ozan,

I'm not sure, but I may have made some mistakes in those voltage measurements (conflated one resistor with another) because I checked the voltage across L267 and it is nearly zero.

I just did a bit of looking further down the signal path and found that the base of Q305 is about -0.5V instead of +0.27V as shown on the schematic. I suspected Q293 might be responsible (in part) for that and I pulled it. It checks "ok" on my component tester; however, with it out of the circuit, the base of Q305 is now a bit closer to the positive value on the schematic. I think it's around 0.5V but I didn't write that down so I'd have to check for a more precise value.

At any rate, with Q293 out, I now get what appears to be a single-shot trace. At a slow sweep speed (e.g. 1s/div) I can switch the display mode to AMPLIFIER and then back to TIME-BASE and can see two dots moving across the screen (using the calibrator as input so two dots makes sense). This isn't the case with Q293 in place.

Am I chasing a ghost or is it possible there's a problem with Q293 that my component checker doesn't reveal? Note that CR299 is also at play at the base of Q305 and I'm now wondering if that might be part of the problem.

BTW, I put a 220-ohm across R394 which brought it down to 50-ohms but that didn't seem to change anything. I'm wondering what the true values of the decoupled voltages should be. The schematic simply shows them as their standard values (e.g. +15, -15, etc.) and I'm not sure what should be the correct values. I haven't found anything in the manual that defines that either.

Thanks,
Barry - N4BUQ