Electronics > Repair

Power board of an old Bernina sewing machine

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richard1950:
Hello All from the Netherlands!

I have a Bernina 1090 with a power board L1230 240V 0789E which is mentioned in the topic 137 by ollihd. It has a slightly different layout.  I have also the problem that the machine is not starting. Even worse: I seem to have a shortcut as the fuse is blown every time. I have replaced already all the capacitors and the diodes in the first stage rectifier. I have also replaced the Power Mosfet (2) and the Silicon NPN power transistor.  I am at a loss as I also cannot find a scheme of the board. Please help. Thank you very much

Don't mind the lose end of one resistor (R11) this was for testing purposes to find the shortcut.

By the way: The resistance between the power input is 4-6 mega ohms (so I don't understand why the fuse is blown)

I have added the schematics of a almost simular board. Perhaps this could help.

tooki:
Blurry, low-resolution images make it very difficult to provide help. Take clear photos, front and back, using bright, soft lighting that avoids shadows. And then don’t shrink them to 640x480, do something reasonable like 1200x900 to 2400x1800.

We can’t identify threads by ID, and even if we could, it’s unlikely that “137” is correct, in that this forum has nearly 200,000 threads, and 137 would have to be extremely old. Just post the URL if you want to refer to another thread!

When you say “all capacitors”, do you mean just the electrolytic caps, or all the film and ceramic caps as well?

I assume that by “shortcut”, you mean “short circuit” (often abbreviated to just “short”)? (A shortcut is an easier or faster way to get somewhere.)

richard1950:
[ Specified attachment is not available ]Yes you are absolutely right. So I will add better pictures. It is indeed a short. Or too much current for the fuse. And indeed I have replaced all the electrolitic capacitors and the X2 ones.

richard1950:
some more pictures:

tooki:
Thanks, much better! Still a lot of shadows, but practically everything is legible now. And at least at first glance, nothing obvious stands out.

Does it blow the fuse if you power it up with no load connected?

Have you tested the other diodes on the board to see if they've gone short?

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