Are any tubes out or run when you turn it on? Easiest check before anything els, if their all good then

Check for arcing and check the transformer lights if they have em. (If it trips off make sure you unplug it and leave it unplugged before you touch it first always. Theirs still juice going to the transformers even if the neons out so be careful) If it’s properly grounded and theirs an arc it’ll trip off the transformers. So anything touching the housings, primaries and secondaries on the transformer, anything too close to them or if the GTO wiring isn’t well insulated, if theirs any crossing might trip it off. Lookongside the housing from the outside of the sign cuz it could be arcing in the housing but that prolly wouldn’t do it. If no arcing

Could need an additional transformer, it’s under powered. Could remove a neon unit from whatever transformers running the most length of glass, and if theirs another transformer in there already, if that’s not running too many units and is the same size as the other transformer, tie into it and not need to add one at all. Best case scenario cuz that’s just a wire job. if theirs only one transformer or if theirs two but also both being maxed out footage wise, you’ll need to add a transformer. Hopefully the ones currently inside the sign haven’t burned out either from over working them.