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Power Supply Fabrication

Fabrication Info

DifficultyRating: 6 / 10

Components 33
Resistors 7
Capacitors 4 Ceramic, 6 Electrolytic
Diodes 8
Transistors 0
ICs 4
Other 1 Trim Pot, 9V AC WallWart, TO-220 Heatsink, 2.2mm Power jack

The power supply is the most important part of the x0xb0x. Take your time and do this right! If you get stuck, download the schematic, and follow along with the PowerSupply page so you can understand what the circuit is doing. This will give you an idea of what went wrong where.

Solder with the power disconnected, and test with the power connected. Also, the 2200uF caps are going to need to be discharged. Ideally you should use a 100 Ohm resistor to touch the 2 terminals of the capacitor together. A screwdriver also works, but it may cause problems later. With a screwdriver, you will see sparks!

Power, 5V and 6V Rectifier, and SmoothingCaps

Solder in the power jack first, and make sure you use lots of it. If you are going to mod in a power switch, now is the time to do it. Then solder in the four 1N4001 diodes (D40-D43), and the 2200uF caps (C3, C5). Then test that the voltage across the jack terminals is roughly 12V AC. Note that it could be as low as 10, or as high as 14.

The voltage across each capacitor should be about 15 Volts DC. Again, this has give. Finally test that the voltage across the middle pin of where IC20 will go, and the left pin (with the white dot) is higher then 8V DC. (probably around 13, but YMMV)

Next, you need to bend the pins of IC20 back, because the heatsink needs breathing room. Solder it in (mind orientation!) and then solder in the .1uF capacitors (C4, C6). Now, test what you have done, by checking that the voltage across C6 is 5V (+/- .5 V).

Solder in the 7806 (IC21), again watching for orientation, and solder in the other .1uF caps (C1, C2). To test, verify the voltage across C1 is 6V (+/- 1 V)

The 5.333 Voltage reference

Does it have to be exact?

If your multimeter doesn't have the thousanths decimal place, you should be fine with 5.33 Volts. See if you can find one later on down the road and recalibrate later.

Solder in the rest of the components of the power supply. Next, power it up, and calibrate the 5.333 supply. This is done by attaching your multimeter to Pin 1 of J4, grounding it (A good place to ground is R179, on the side opposite of where the power jack plugs in) and adjusting TM6 until you get 5.333 Volts.

Finally verify that the voltage at pin 3 of J4 is around 12 Volts. The voltage should actually be 11.851V. (there is probably some tolerance here as well)

Common Mistakes

/home/ladyada/public_html/wiki/data/pages/x0x/psfabrication.txt · Last modified: 2016/01/28 18:05 (external edit)