Well, if you've already opened it up, and you have a meter, you can carefully check for transformed power. The power cord connects the transformer to the wall outlet, so there is always AC power to the bridge rectifier/capacitor and small main-board connector (34 and 18 VAC, I think) when it's plugged in to the mains. The DC from the bridge rectifier/capacitor connects to the main-board screw terminals and is fed out to the cell by the power relays. The 18 VAC is rectified on the main-board, and feeds 12 and 5vdc regulators for the relays and micro-controller ( mine had a SONIX mcu.) You have probably had a component failure in the 5vdc circuitry.
Check the small fuse on the 18VAC in feed for continuity, if it opened, replacing it may allow it to work for a while, but probably not.
If the transformer and rectifier/capacitor are still good, there are several "hacks" that will allow you to power the cell and generate chlorine by bypassing the control board. Not for the feint of heart, as most will bypass the flow detector too, leaving open the possibility of a hydrogen gas build-up and possible catastrophic explosion, should a spark occur in the gas bubble inside the water filled piping. It has, apparently, happened before.
The easiest "hack" is to land the cell wires on top of the rectified output wires. Now, when ever the unit is plugged in, the cell is powered ON. Plugging into a lamp timer gives you some control of ON/OFF timing. If you want to reverse the cell polarity to "self-clean" (the unit did that every 20 hours, according to my manual) you can unplug the cell power cord and turn it over, every 5 days if you run it 4 hours per.
Or, just buy a new unit and keep the spare parts from the broken one.
I'm still waiting to hear from anyone that has plugged an "old" large Intex cell into one of the new units. I think that the controls will fault on a high or low salt measurement, do to the difference in cell plate area. If it works, that would be a sweet way to upgrade the controls and output.
Anyway, be careful, and good luck!