Electronics > Repair
Power board of an old Bernina sewing machine
tooki:
And the one to the functionally identical Bernina 1130, on which the 1090 is apparently based (according to the 1090's service manual).
richard1950:
Thanks for the information. I have decided to connect the board to a low voltage transformer (16v). Still the fuse is blown. After replacing it with a stronger fuse I can now check the short by switching for a split second and see what happens. I took out one by one components to see if this is the problem. I know now that the problem is in the high voltage part. The low voltage part seems to be ok. At least after taking out transformer U146 there is still a short. I took out Diodes, the U145 transformer C67, D104, T126, D105, C65, R58 (wire only) and still no result. It could be one of the transistors T123, T124, or T150. That I will try next. But this are really one of my last opportunities.
richard1950:
I got the print working again! Thanks to the assistance of Gerard Boom, a friend from the local Repair Cafe who managed to find the problem within an hour. Two rectifier diodes which I replaced were again faulty and the diode D117 had a shortcut.
After installing the print works. It seems only that one of the sensors is either broken or not correctly placed at the machine is making strange movements. But that I will sort out hopefully.
Thanks for the assistance!
tooki:
Thanks for taking the time to provide an update. (People often neglect to do this, so it's much appreciated.)
How did he diagnose the problem? In particular, I'm curious as to how he found a diode that failed short, when you stated earlier that you tested all the diodes and they were fine.
richard1950:
In the end I removed the main transformer between the high voltage and the low voltage circuit. My friend started again from the beginning by testing the main rectifier first. At that moment he found the two faulty diodes. He tested, like me, with low voltage. Now the high voltage circuit was working again he looked for the low voltage circuit and found the main diode faulty by measuring in place.
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