Okay, here's the thing: Zenith servicers hated that toilet. There, I said it...
I remember getting two bad 186 modules in a row from Zenith. If you can find a new (yellow label), grab it. Any red label version was "rebuilt" using questionable techniques.
Take a look a the board/metal plate assy the 186 sweep board is mounted to. There are three TO-92 start-up transistors on the small board near the top edge. See if they are blown. If they are, replace all the electros on the 186 board as well as the transistors (and IIRC, a resistor or two will be scorched). There is a lot of voltage on those transistors so choose your subs wisely.
On the main 181 board there is a dual section PC mount electro. Good probability one side is bad if it's never been changed. If one side is bad, it causes all sorts of collateral damage when it opens including tormenting that start circuit and blowing those transistors.
If all those are good, turn the main board over and resolder every heavy resistor on the board. They usually are mounted in small metal grommets before soldered. What causes many guys to miss this is that the connections look fine, even under a loop, but they go bad. Put some liquid flux on them and reflow them with a decent wattage iron.
If you had the boards out, don't overlook the possibility of getting a connector crossed. The boards are printed so carefully check the legend on the board to the connector number. Fortunately, Zenith was good about clearly labeling those connectors.
John