Winding the Transformer


Here's the diagram:


First step: Remove the transformer from the power supply and disassemble it.
You need to desolder the transformer from the power supply. If you don't have a solder sucker, this isn't going to be easy. I'd reccommend you get one, because it comes in handy.
Once you remove it, throw it in the toaster oven at 300F for a few minutes to melt the glue. After the glue is melted, grab some pliers, and it should slide apart without too much force. Be careful, the e-cores are very easy to break!



Next, you need to unwind what's currently on the transformer. The yellow stuff is just tape. You should be able to unwind it pretty easy, unless you cooked it too long and made a sticky mess. You need to take note of which coil starts on which two pins, and how many wraps it has.
Unwind it one layer at a time, there should be three layers, for the 3.3V, 5V, and 12V, each being a different number of wraps. Next you'll get down to the primary coils, which should have 40-50 coils.
Also, you might run into a middle layer, with a copper sheet like mine had. I just removed it, and everything worked fine.



Once you get everything off the bobbin, it's time to rewind it with new layers. The first layer is the new primary coils. There are 3 coils, each having 3 turns of 18 guage wire doubled up. Two of the coils are for the IFR540's, the other for the diode connected to ground. Once I wound them, I wrapped them in tape so they wouldn't move. Also, you'll have to use a razor or knife to strip the ends, so you can attach wires.



Next, you need to wind the secondary coils. These are the 3 coils for the 3.3V, 5V, and 12V. You'll need to double the number of wraps you unwound at the beginnging. Mind had 3 wraps for +5, and 4 wraps for +12 (it was AT, so no 3.3V), so I rewound it 6 times for the +5, and 8 for the +12. I used 21 guage wire, doubled up, which worked fine. If you're pushing a lot of current, you might want to triple up the wires, just in case.



Finally, put the e-cores back on the transformer, tape it up, and wire it up to the power supply. Hook up the wires to the two optocouplers, and the +12 and ground to a battery or another power supply. You'll need to throw a few fans or an old just hard drive or something to put a load on the power supply. Once you have everything hooked up, turn it on. If there's no smoke or fire, that's good!
You'll have to adjust the 10k pot until the voltages are right. Hookup a multimeter, and adjust the pot as nescessary. If one voltage is right, but another wrong, then you didn't wind the transformer properly. You'll have to redo the secondary windings, and add or take away wraps until you get everything right.
If your power supply doesn't do anything at all, check and double check your wiring, then e-mail me or presslab if you need to.



I wish you luck. If you have any questions or see any errors or anything, send me an e-mail.

- Robert Bean
arby@tamu.edu