I must have an older design Duratool zd-917 .
Mine has a single 50hz transformer for both sides , powered by two opto coupled boards ,each one using a mosfet behind a bridge rectifier to control the ac power to the element. Controlled by two boards with a silabs 8051 for the logic and a holtek driving the display.
It looks like two d000673s in one box.
Nippon - zhongdi make the Duratool models ..they seem aimed/designed to be more hobbyist that professional.
Yes they replaced the transformer with two SMP modules 240vc to 18v @ 20A (bit optimistic I think) and added the Mosfet circuit to the same pcb.
The front panel and the 8052 control & display are the same.
In use they are very good and take less space than my old Weller DS900 and I use the ZD-917 as its easier to keep clean (maybe I will put the Weller on e-bay) just seen one sell for £82
My old boss just phoned he must be following this topic, and has said I can have 3 of the old 917 units, they only repaired one, plus 5 soldier stations using the same modules.
Bet he don't give me the gun & iron to go with them.