Power supply design question 2 / 2 - 120V conversion

[metertech58761]

Here's the second question I have on this circuit.

Before continuing, as we're talking about mains voltage, I want to make it clear I have NO intention of doing ANY modification, but I want to get an idea of how it would have been done.

There is NO chance of the original manufacturer documentation surviving, as the original manufacturer sold the division that made this product in the late 1990s, a few years after they officially moved this particular product into 'end of life' status. Any information the buyer did not take in the transaction would have been discarded when the original manufacturer moved into a newer facility. Even so, the buyer did a major housecleaning some years back and purged any information on long-obsolete equipment (and their last remaining examples of same).

Anyway, if you look at the schematic, you can see it was designed to be powered from a 240V 3-wire circuit, the default voltage provided to residential services in North America.

Line 1 would connect at E22, the neutral at E21, and Line 2 at E24.

However, there are a few cases where the customer would have an older 120V 2-wire circuit, and looking at this circuit, it appears that this could be reconnected to configure the unit to work properly with just one hot wire and the neutral.

PW1 is a trace that could be severed if necessary, E11, E19, and E20 are pads on Panel B and D that are not connected. Also, W1 and W3 are jumper wire pads, with pin 1 being the larger of the two pads.

I could probably reason this out myself, but I want to see if anyone else would be able or willing to try and suggest how this would have been done.

Again, I have no interest in trying to do the conversion as some of the bespoke coils change value for 120V operation (I know this as I was looking up something else and chanced across a notation of parts values for the 120V / 240V versions of this product). I just want to know how it would have been done.