I have had an Apple IIe for several years now that I power up and play around with from time to time, but not on a regular basis. I went to power it on one day recently and found it be completely dead. I decide to open it up and check for power coming out of the main harness from the power supply, but get nothing on either the 12v and 5v rails.
Tearing into the Power Supply I see no obvious signs of failure. I check the fuse, it's still intact, not blown. The electrolytics look pristine on the outside, so before I blindly replace them I wanted to get to the bottom of the failure, although I do start with replacing the RIFA capacitor(low effort to do so) near the mains input as they are well known components that fail in numerous electronics. A new film capacitor made by TDK installed, no change in the output, still dead.
I manage to pull the large Q2 transistor off the board to test it out of circuit. No shorts there, all voltage flows in the correct directions (or doesn't) between Base, Emitter, and Collector.
I test the resistance in the windings of the transformers. The main, largest transformer, T2, checks out on all it's windings. The smaller Transformer, labeled T3 however has a high resistance on what I can only assume are its primary windings. I manage to remove it from the board and test it out of circuit. The set of 4 pins are completely open it seems on both sets of the windings at those pins. No continuity at all and no reading when checking Ohms. I know this transformer has to do with the PWM control, which is likely why I am not getting any output from the main connector harness.
This problem seems to be similar to the situation described in this persons blog: https://www.jammarcade.net/tag/apple-iie/ Clearly, there is a break in the windings on this transformer, but I CANNOT see them visually on either of the pins, so they must be inside the windings, or somewhere I just can't see yet.
Has anyone else encountered this problem and found a suitable replacement transformer? Does anyone have a clue what it's specifications are? I imagine this component is custom made by Astec many years ago. Best I can find is a Vendor No. 852-10200680 from an Apple information PDF on these power supplies.
If I have to determine what the number of windings on either side should be, I'll go down that route and try to report back here with my findings for the next guy.