Hello, folks. I need your help in repairing a faulty motherboard from a PFAFF 1471 sewing machine, circa 1986. The basic problem is no power. I tested the 120 volt supply lines all the way from the power cord through the housing connectors and into circuitboard. I got good continuity and voltage throughout and at least into the transformer. Hard for me to test further than that. I suspect one of three things:
1. The three 240 volt .630mA fuses are blown. They are measuring about 12M, 6M, and 6M ohms respectively. Aren't fuses supposed to have full continuity unless blown and thereby open? Or do thermal fuses behave differently? I realize the fuses could be blown but the cause for why this happened is more important and would be the bigger concern. I just need to understand how the thermal fuses work.
2. There are two identical components next to the sealed and soldered transformer. I suspect this to be voltage regulators and I see very crystally yellowish crud where it meets the circuitboard. In case I can't attach some pictures, it's flat black ceramic type with four prongs. It measures about 5/8" by 3/4" by 3/8"". The numbers on it are G1 KBL01 8615. I don't have a schematic and am trying to identify and obtain a replacement. I'll contact a sewing repair place and PFFAF soon to see if they can help me. Any ideas on where else to obtain this part or the entire motherboard? How can I troubleshoot this part?
3. The transformer is dead, in which case I'm dead in the water, too.
I'll try to upload some photos. I didn't have any luck in my last posting but I'll try...
1. The three 240 volt .630mA fuses are blown. They are measuring about 12M, 6M, and 6M ohms respectively. Aren't fuses supposed to have full continuity unless blown and thereby open? Or do thermal fuses behave differently? I realize the fuses could be blown but the cause for why this happened is more important and would be the bigger concern. I just need to understand how the thermal fuses work.
2. There are two identical components next to the sealed and soldered transformer. I suspect this to be voltage regulators and I see very crystally yellowish crud where it meets the circuitboard. In case I can't attach some pictures, it's flat black ceramic type with four prongs. It measures about 5/8" by 3/4" by 3/8"". The numbers on it are G1 KBL01 8615. I don't have a schematic and am trying to identify and obtain a replacement. I'll contact a sewing repair place and PFFAF soon to see if they can help me. Any ideas on where else to obtain this part or the entire motherboard? How can I troubleshoot this part?
3. The transformer is dead, in which case I'm dead in the water, too.
I'll try to upload some photos. I didn't have any luck in my last posting but I'll try...
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