The diode addition is around Q664, half of the slope comparator pair of transistors. (B-time base) There is also an extra resistor. The soldering looks very neat, as if it was done at the factory, but I suspect someone else added these.
I could post a photo, or a sketch, but maybe a brief description would be enough to jog someone memory.
The extra resistor is placed along R665, one end connected to R665, the other end to R653. The two diodes are connected in series, One end of this series is connected to R665, the other to D653 and R653. D653 has a fine wire coiled around it and soldered to each lead on the diode. One of the two extra diodes has the a mark in the middle of the body, but no cathode mark is visible; it is glass-bodied. The anode of the other one is connected to R665.
Any ideas on why this extra circuitry is there? The slope switch for the B-time base works as expected when the B-Sweep Mode switch is in the "Triggerable after Delay Time " position., but not when it is in "B-Starts after Delay Time" position. The manual is not specific on what position the B-Mode switch can be in (works both ways or not), but my guess is that the slope should change in either position using the Slope switch. Same goes for the level knob (for B) -- it only works while in the "Triggerable after Delay Time" setting.
Unless there is a good reason to leave it in, my plan is to lift the leads and see what happens. I'll leave the fine wire around D653 there.
