I have a Bernina 340 Deco embroidery computer. I am having trouble (lots) with the thread looping on top of fabric.

Take it in for service. There is no reset procedure.

https://www.bernina.com/de/SupportData/bernette/deco-340/deco_340_EN_04-13.pdf

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Um, the top thread is showing on the bottom of the fabric? The top tension is too loose. The two threads create a tension battle, one pulling against the other. To pull the bobbin thread up, tighten the top tension. The tension is accurate when the two threads meet "in the middle" of the fabric. On thinner fabric, you might see a tiny spot of bobbin thread on the top and a tiny spot of top thread on the bottom.

Service manuals are difficult, if not impossible, to find as they are intended only for technicians. You may be able to find one for sale somewhere, ie eBay or some other web site, but the likelihood is low.

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Punctuation in embroidery is sometimes tricky. Perhaps using downloaded software will give you other options.

Bernette 340 downloading internet files

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&ved=0ahUKEwjV3MKYgJvMAhXpvYMKHQ7KCAEQFghHMAk&url=http%3A%2F%2Fsneedswv.com%2Fworkbooks%2FMyBERNINA-1-Embroidery-Workbook-111513.pdf&usg=AFQjCNEE8r8hvaAyOXc_iHEowULaAYe5nQ&cad=rja

Bernette 340 deco Fonts Bernina

Bernette 340 Deco Embroidery Machine

According to the manual for the Bernette Deco 340, the machine only reads .EXP+ files. ART files need to be converted to the EXP file type using the Bernina Embroider Software. (Even the designs on the Studio Bernina CD need the ART files converted to EXP.)

The manual is available from the Bernina support site: http://www.bernina.com/en-US/Support-5/Machines-en/bernette-deco-en . The direct link to the manual is http://www.bernina.com/getdoc/c6cc51e0-d5e9-4cb1-a7be-f164c0f4fdff/deco340_EN_GZD . (Note: you will need Adobe Reader or a similar program to access the manual.)

I'm surprised that you were able to get any .art files to work until recently.

I hope this helps.

Cindy Wells

BERNINA ArtLink 6 Embroidery Software
It is free and has output for DECO 340

either try rethreading machine from beginning... or your top tension is too loose... did you switch it over? I have a Singer futura and I have to switch a couple things around for sewing or embroidery...hope it helps

You should use some klnd of stabilizer under your hoop. I use the paper kind which is thin or there is a heavier tear away stabilizer. I have used all cotton thread for embroidery or you can use rayon. There is a finer thread called bobbin thread for the bobbin but I gernerally use the same as on the top so it will be the same. Are you using an embroidery needle? .As for your thread getting wound around the bobbin the only thibng I can think of is tht it is threaded incorrectly. if it isn't the lack of a stabilizer. I hope this helps but I think it the the lack of stabilizer that is causingyour problems. The needle is going in and our of the same hole during embroidery and is getting stuck on your bobbin. Let me know if this helps! Suz

Upper tension is too loose or lower tension is too tight.This might be a good thing. It depends upon how much it is pulling the thread under. A perfect tension on embroidery is about 2/3's lower thread and 1/3 upper thread showing on the bottom.
sewman7

If it was an upper tension problem your loops would be beneith the fabric. Since the loops are on top this tells me the lower tension is too loose. There is a small screw on your bobbincase that you need to turn clockwise to adjust it. Do the adjustment little by little until its good. I would do it like a clock. First turn the screw to one o'clock. Still looping? Go to 2 o'clock etc.
If this doesn't help you, a clean opikl, and adjust by your local dealership could be anywhere from 50.00 to 90.00.
Good luck