Got a "garage sale" SA-6700 today. Fuses blow as soon as the power is turned on. Checked the transformers, as best I could. Doesn't seem to be a dead short in either primary...around 3 ohms resistance. Then I checked the diodes (D21 thru D24) all GP-20D. All of them were open and failed the test. I've ordered replacements from Digi-Key. With ALL the above mentioned diodes removed from the circuit, I can turn on the power and the fuse doesn't blow. That's progress. My question: OK, what are the chances I've found "the" problem, or have I just discovered one of the symptoms and as soon as I power up I'm going to get more blown fuses and/or blown GP-20D's, or other surprises? I will use a dim-bulb tester on power-up to lessen the flames that may result. Any insights? Any advice?