On the last three weekends tried to fire up the LTN72 using my 1500W inverter and a separate supply for the accumulator 28V input. The power supply alone if supplied with 115VAC starts drawing 20W above a certain voltage (100VAC approx.) and it also creates a "switch mode typical" sound, but no voltage shows up at its outputs. You may see and hear it here:
and I may be missing some other input to the supply to actually create its outputs.
Back within the unit itself and with input of even 125VAC, the
LTN72 unit does not start up, too -
(0:12 Inverter on, 0:20 switching from Off to StBy, 0:30 back to Off). Again only around 20W of power drawn on the INU 115VAC input, no power drawn on the 115VAC heater input and no power drawn on the battery input. Checking the battery input I can measure that there is a cap inside the LTN72 that is getting charged upon applying power.
Last weekend I checked the supply's internals (everything looks OK, no blown up caps etc) and the power rails do not seem to have shorted caps on them (checked the 5V digital and the supply for the OpAmps within the LTN72RH).
So for the moment I will set this project to the pause state and reach out to some people - maybe someone out there has got SCHEMATICS at least of the powersupply or input section of that unit. That would save lot of time over reverse-engineering that beast without knowing whether there is more trouble ahead with broken gyros/accelerometers etc.
Stay tuned...