That is my guess as to the problem. Mine did exactly the same thing. I have a very old one and a very late model one as well. The old one had the Brown transformer, the new unit has the Black one. I found the power in wire to the HV transformer and put an ammeter in-line to read the current draw. I will look at the schematic and tell you which wire I used. What mine did was started out at a low current draw , the unit worked fine, and as it heated up, the draw slowly increased until the power supply finally tripped. I don¡¯t remember the exact current draw numbers. BTW, I have a prototype transformer in the works to replace the brown transformers. I will put you down on my list as potentially needing a replacement for yours.
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Michael Lynch
Dardanelle, AR
Mlynch001