I made a new power supply for an MC-101 using 2 separate fuses, one for the low end, 0.125A and one for the high end, 0.5A. The voltages are ok. The 0.125A keeps blowing. Would the 10v AC pull more than 125ma or is it more likely a problem in the rectification circuit? I don't have a schematic (it seems that on one does)
Do you have a Variac or DBT? If so, replace the 0.125A fuse with a 10-ohm resistor and power up using the Variac (preferred) or DBT (with very low wattage bulb, 20w??) and "see" what the voltage across that resistor is. Then you can calculate the current being drawn with Ohm's Law. 10ohm resistor will heat up and smoke pretty fast, if you are drawing more than 1/8w (using 1/4-1/2w resistor) while at the same time limiting the current flowing into the circuit. I wouldn't keep power on long, unless you can use a Variac, but will give you guidance if you need 0.25A fuse, or if there is an actual issue with the supply. Could be as simple as the turn on current inrush is too much for that 0.125A fuse, but sufficient once the circuit is powered on and idling.
YMMV, but this is what I would try after exhausting all other ways, such as DMM measurements and manual calculations walking methodically through the schematic/PCB.
YMMV, but this is what I would try after exhausting all other ways, such as DMM measurements and manual calculations walking methodically through the schematic/PCB.
Thanks; will try; have variac but no spare resistors; don't have the schematic. Was hoping not to have to re-invent the wheel.
Well, I kinda' solved my own problem. The original p/s for the MC's had only 1 fuse, I assume 0.5A. I put a 0.5 A fuse in and voila! it works, but a funny thing: The indicator light, when lit, has the unit off and when the light is off, it's on. Is that the way it's supposed to be? I had an MC-101 years ago but I don't recall this "feature".