Blow 270 ohm 1 watt resistor in power supply with every turn on

[ashura]

Hi. I have had my crack with speedball up and running for a while. I upgraded to film caps and bypassed them with no problems. I also added the Cree diodes with no problems. Then I decided to repaint and rewire the whole thing with cloth covered wire. Now with every turn on I blow the 270 ohm 1 watt resistor in the power supply on the last cap. Help. Also, should I have 120v at terminal one or two on the transformer. It seems like it should be terminal two as it is labeled 120 on that terminal but I am getting 0 volts there and 120 at terminal 1 in the transformer. I verified that the wiring is correct.

[Paul Birkeland]

Hi. I have had my crack with speedball up and running for a while. I upgraded to film caps and bypassed them with no problems. I also added the Cree diodes with no problems. Then I decided to repaint and rewire the whole thing with cloth covered wire. Now with every turn on I blow the 270 ohm 1 watt resistor in the power supply on the last cap.

That resistor is not supposed to be 270 Ohms.

-PB

[Rocketman248]

Should be 270K ohms if I remember correctly.

[ashura]

Thanks! I suppose such a large difference in resistance would cause that now wouldn't it! I had bought new resistors to replace the old ones instead of reusing them and got the wrong ones.

[Paul Birkeland]

Yes, 270 Ohms is a lot different than 270,000 Ohms.  270 Ohms across the power supply will draw just about 1 ampere of current.  The Crack circuit draws about 0.080A of current.

That resistor will dissipate 270 watts, at least for the few tenths of a second that it can before it vaporizes.