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To convert the TuxScreen wall wart power supply (PSU) to 220v. Change the 220uF/200v cap to 68uF/450v and the MOV to a 275v version. Mount all in a new box with a IEC male connector, now you've got a universal 110/220v PSU.

SquarT says: I used a 100uF/450v cap, because 68uF isn't available here. I took the chance to just try it, and no flames burst out when I plugged it in the wall. I did make sure the voltages on the pins were still correct, and they were. The tux is running for almost an half an hour without problems now. The MOV gets warm and the little heat-sink gets quite hot (not able to touch it). I assume it is normal for this heat-sink to get hot. I did not bother to check the temperature on a 220v/110v converter (converter is lying at the office), although the case is getting quite warm on the outside of an unhacked power supply. Oh well, it is still running... [Next day]: Checked the temperature with my multimeter. It reads 60 degr. celsius. Might be slightly higher, but seems to be within limits.

At first I did not change the MOV and it blew up taking the fuse with it!

The PFI seems to work, but I've not checked it with a CRT, my TuxScreen phone key pad works!

The main IC is a (Fairchild) KA1M0280R (labeled 1M0280R) switch mode PSU controller, for which Fairchild have a couple of application notes detailing universal PSU's. The circuit of the PSU seems to be very similar to the reference design on page 10 of http://www.fairchildsemi.com/an/AN/AN-4106.pdf (see also http://www.fairchildsemi.com/an/AN/AN-4105.pdf), but with the addition of the PFI circuit.

In the following image, the MOV is the blue object to the left behind the 2 black wires and the 220uF/200v cap is the large capacitor to the right.

http://tuxscreen.net/img/mvc-634f.jpg

AdeDavey would like to known the part number/manufacturer of the MOV used.

AndrewYourtchenko comments - MOV is an optional device if you want to protect yourself from power surges - in normal conditions it is unneeded. Yesterday I've hacked my 110v power supply by installing 2x220uf/200v capacitors chained together, instead of the one that sits there. seems to work fine. ...And I've burned the MOV that came with the power supply and just had to cut it away.



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