If the VFD is actually bad, then it is beyond practical repair. The VFD is sealed. The red lines are the heater for the VFD. The heater usually runs on a lower voltage than the VFD itself. So if the VFD has red lines, the heater filament is drawing more current than it is supposed to. That means the heater filaments themselves or bad or the voltage driving the filaments is too high. One of those circuits on the climate control is probably in control of that.Wow, you clearly know a lot about electronics! I recently tried to fix one but kept getting the red lines and overheating R38. Is it true that it's possible it is beyond repair if the VFD goes bad? Information on repairing these is very scarce and sources often have differing information. Thanks!
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In my experience with a few of these, most problems come from C14 and C15's electrolyte eating traces. If you don't clean the corrosion and repair the traces, you will never have a working display.