It occurred to me that I was measuring the resistance of the primary side of a step-down transformer, so the resistance will be rather high.
You're making DC measurements on the primary of a transformer. It doesn't matter what the secondary is.
Ed, I'm not sure how you measured only 3 ohms on the primary. That seems absurdly low...?
No, it isn't. I wandered around and made some measurements of the primary circuits of a few devices as follows:
HP 6622A Linear Power Supply (160W output) - 0R9
HP 6002A Linear Power Supply (200W output) - 0R8
Goldstar GP-505 Linear Power Supply (250W output) - 1R0 -- This is the unit I originally measured. Looks like the switch was a bit dirty when I made my initial measurements.
Then I measured a mil spec. hermetically sealed 360W isolation transformer. 110V in, 110V out. Nothing else. It measured 1R6. Note that unlike my initial measurement, these measurements do NOT include lead resistance.
Are you beginning to see the pattern, Matt? Your power supply has a total output of 195 watts so you should be seeing similar numbers.
That being said, there is continuity between all of the primary taps, there just seems to be a high resistance (higher than expected - ranging between 600K and 1M) between the hot "leg" of the transformer and the taps. Perhaps this is normal but it still strikes me as a little high. I'm a bit concerned that it may point to a damaged primary winding which I assume would be BER.
These devices that have 110/220 switches typically have two primary windings. They run in series for 220V or in parallel for 110V. Since the 3303 has 100/120/220/230 volt settings, you should have a total of 6 wires coming from the transformer to the voltage selector. That's consistent with your drawing showing J102 and J103. But the gray wire doesn't seem right. Can you recheck that? With J102 and J103 unplugged, is there continuity on the transformer side of J102 and J103 between them or is the continuity only within each connector?
Don't forget that you've never seen this thing working. Maybe someone else got to it before you and messed up the wiring.
Also, for the record, some of you seem to be talking down to me like I'm a complete newbie. I wanted to make it clear that I am an Electrical Engineer by profession and understand the basic concepts behind the design of power supplies. You can speak in technical terms and I will understand, you don't have to dumb it down for my sake. This is just the first power supply I have ever tried repairing, so it's a learning experience for me.
Oh, an Electrical Engineer. Okay, I'll take it easy on you. After all, we Engineers have to stick together!
Seriously, on a forum like this, there's no way to tell if you're talking to a kid in high school or a grey beard who's forgotten more than most of us will ever know. I really do have a grey beard, but I haven't forgotten everything ...... yet ..... I don't think.
Ed