How to ground a wire programatically with MDBT42Q?

Sun 2020.05.03

Thank you for making the observations and taking the time to poke around a bit. Three points to review, and to make sure we are both communicating.

Is the voltmeter an analog needle type or a digital LCD type? Black ground and Red positive probes?

Regarding R18
If one takes a look at the schematic upper right, R18 connects one side to the positive rail 11V and the other to supposedly the end of a potentiometer. The trace exiting to the left runs down to X2-4 MK where the drawing of the emitter is now connected. I say supposedly, under the assumption the resistor running E-W just above KE and below the silk screen C16 is the 180 ohm (brown-grey-black with black zero multiplier - color too off to be sure) appears to connect to the wiper of PK2, as it is immediately centered between the tabs of PK2, those being just North of the pot itself. Having access to the underside would be nice to verify but isn't necessary. So, electrically, the screw terminal MK is the same point as where the vertical trace in the schematic connects to R18. Then placing the black ground probe to MASA and red positive probe to MK should provide est 6-9V which is actually the drop across the pot, but would provide the value at R18. Would like to confirm so that we know what the transistor is connected to and the range it will be swinging.

'Just to confirm, the X2-1 will be the black slot with label "1" on top'

I'm glad you pointed this out, as I didn't double check the schematic terminal block X2. The schematic seems to be for the board with the blue terminal block as it has eight pins. The photo with the black terminal block only has seven. It appears that is a variant or a knock off of the original. Double checking the schematic, I missed that X2 has eight pins, but the board only has seven screw terminals. The big mystery, where is the positive 11V X2-1?

Glad you pointed that out, but don't have a good idea where to get at the 11V yet. I'll continue to study.

Now the two black wires dropping down from the transformer are the input to the AC section which is mostly the parts to the lower right of that circuit board. D1-D4 are the bridge rectifier converting the AC to DC. The labeling 1 and 2 are likely what we see on the left side of the schematic as X1-1 and X1-2. (also not exactly matching) Putting the voltmeter in the AC position on a 20-50VAC scale and on each of the black wires will probably show est 12-24VAC as a S.W.A.G. (silly wild arse guess) and would a connection bewteen MASA and that pin 1 been made, wouldn't have been wise and we might have seen you in the next ElectroBoom episode as we would have been grounding one side of the inbound AC wave. Electrons would not have been happy. Very excited though! Depending on the meter type and which scale it was on, might have damaged it.

It's likely that C16 and R17 are part of the five second delay you mentioned with PK2 adjustable for that delay interval.

Curious, what is the voltage between MASA and X2-7 MU ? (11V ? maybe)
As that pin is connected to R15 180 ohm and then to the other side of the LED, (which by the seems to be labled backwards as the anode side is to ground, so I don't see how it could ever illuminate - me thinks schematic backwards) we may be able to use that as the trigger point for our base resistor input. For an NPN we will need a positive voltage greater than the drop across it's emitter to turn it on, the equivalent of when you were just using the jumper. The emitter would need to connect to MASA though and it's collector to MK at around 6-9V When the transistor is on, we'll have 11-0.7V / 180 ohm or 57 ma current through it. Just over a half watt, but a brief interval, shouldn't be an issue. But R18 in the photo looks like just a quarter watt, can't be sure size wise.