Problem of Ultrasonic Generator of Nonwoven fabric bag makin machine.

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Thread Starter

Shahed1969

Joined Apr 20, 2015
9
Dear All,
These 15kHz ultrasonic generators are rather basic Chinese units (see pictures) used for welding nonwoven plastic (basically thin plastic fabric).
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This Ultrasonic Generator become faulty, I have medium idea about electronics, but fail to repair it.
The Chinese manufacture did not give us any circuit diagram, so I made a full circuit diagram and exhibit here for reference.
Circuit Diagram of Ultrasonic Generator.jpg

After checking I found some power transistor (2SC3998) faulty on Lord amplifier then changed and found two diode on oscilation PCB then change. After that when I run the machine frequency not matching with ultrasonic transducer and nonwoven fabric soldering not possible.

If any one familiar with this system please give me the solution.


Thanks

Shahed
 

Alec_t

Joined Sep 17, 2013
12,249
I'm not familiar with the system, but when you say "when I run the machine frequency not matching with ultrasonic transducer" can you tell us what was the measured output frequency and what is the specified transducer frequency?
Are all the power rail voltages what they should be?
 

Alec_t

Joined Sep 17, 2013
12,249
I can't work out which components, apart from the 'tuning coil', determine the intended operating frequency. Have you checked the 20uF 450V AC cap near the output transformer?
 

Thread Starter

Shahed1969

Joined Apr 20, 2015
9
Yes I have changed the 20uF 450V AC cap, but nothing positive.
At first two diode burns out at input side of ring type transformer and 5 pcs transistor (2SC3998) ans some resistor burns out at input side of output transformer, then I replace all bad component then when I start the machine frequency comes out but not sufficient for soldering. I tried for frequency tuning by tuning coil, it has a tuning knob which move a core inside the tuning coil then frequency up and down in a limited range but doesn't go in sufficient high for soldering.
I think it has some technique for fine tuning.
 

Alec_t

Joined Sep 17, 2013
12,249
The circuit appears to be some form of self-resonant arrangement where the transducer itself partly determines the oscillation frequency. Are you sure that the transducer itself isn't damaged/faulty?
 
Perhaps using an impedance matching transformer between the piezo transducer/pickup and the amp input... i.e. such as a small 8 ohm: 1000 ohm
audio transformer. Connect the 1000 ohm side across the piezo, 8 ohm side to FET via a DC blocking cap (thus allowing the FET to be properly biased).
Good luck with your circuit... hope you get it working without any more troubles..

Addendum... consider using a hi-gain BJT instead of FET, with the transformer mod..
 

strantor

Joined Oct 3, 2010
5,671
This is an impressive help request post. Rarely does anybody go to the trouble of reverse engineering a circuit and making a diagram before posting. Unfortunately i cannot help, but i just wanted to say "thanks" for not posting a blurry image of a PCB and expecting someone to magically diagnose it from across the internet (most people do that). I'm sure there is someone on this forum who can help, with the information you have provided.
 

Thread Starter

Shahed1969

Joined Apr 20, 2015
9
Perhaps using an impedance matching transformer between the piezo transducer/pickup and the amp input... i.e. such as a small 8 ohm: 1000 ohm
audio transformer. Connect the 1000 ohm side across the piezo, 8 ohm side to FET via a DC blocking cap (thus allowing the FET to be properly biased).
Good luck with your circuit... hope you get it working without any more troubles..

Addendum... consider using a hi-gain BJT instead of FET, with the transformer mod..
There is no any FET using in this circuit, using only NPN Transistor (2SC3998).
 
Hello Shahed, this is the first time I write in this forum. I'm working on the same equipment right now.
You have saved me a lot of time re drawing the circuit, so thank you.

I hope that you already solved the problem, if that isn't the case...

Try to run the generator without the transducter plugged. If it run ok without the overload led turning on it might be working but on a different frequency. You should disassemble the tunning coil and see if the ferrite bars are well fixed on the screw, that is a common problem I found on these generator.

Thank you again, Matias
 

Thread Starter

Shahed1969

Joined Apr 20, 2015
9
Thank you Matias Baldo.
I have checked the tuning coil and found ferrite core is fixed as well on the screw.

Now our main problem is every hardware component are OK. But frequency not enough strong to weld the fabric.
I try to adjust by tuning coil but failed.

If you are familiar with this unit please share your experience.


Thanks

Shahed
 

ScottWang

Joined Aug 23, 2012
7,071
Welcome to the AAC forum.

The owners of All About Circuits has elected not to host discussions of transformerless threads.

This thread is against the AAC forum rules, Terms of Service (ToS).

Any kind of over-unity devices and systems
Automotive modifications
Devices designed to electrocute or shock another person
LEDs to mains
Phone jammers
Rail guns and high-energy projectile devices
Transformer-less power supplies
Terms of Service (ToS).

Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

Please try to understand the reasons behind this action, and feel free to browse and use the forums.

You might find answers to your questions in one of these forums:

http://forum.allaboutcircuits.com/showthread.php?t=54400

Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ .

Good luck.
 
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