hi and thank for having me here with you.
I have i circuit board that control the speed of a stand mixer, the problem is when i start the mixer it goes to full speed.
The reference for the board is SM168-S1
Thank you so much.

 

Look to that part which is attached to the aluminum heat sink.

 

Look to that part which is attached to the aluminum heat sink.

Thank you for your reply, that's a BTB12 600C TRIAC

 

If the triac is shorted, that certainly would match your symptoms. Check it with your meter.

 

The triac tests ok, but i suspect a small transistor S8550 (emitter and collector are shorted)

 

are you testing them out of the circuit?

did you draw a circuit diagram?

 

are you testing them out of the circuit?

did you draw a circuit diagram?

yes i did on circuit and out of the circuit, still E/C shorted i will receive the part tomorrow and try again.
thank you for your reply.

 

ok

 

This isn't the problem, the transistors are fine, please help.

 

If you've replaced the faulty transistor and the fault is still there check the replacement to see if that is now shorted as well. If it has then there must be a fault causing that so look closely at the components connected to it. It might be worth replacing the triac even if it measures ok just in case. Is there a number on the ic in the background? If so see if you can find a data sheet & check it's supply voltage (dont forget the board has mains voltages on it). The power supply is probably directly from the mains via a capacitor and/or resistor, limited by a zenner diode- check the voltage across the zenner. Also the controller seems to be a multiway switch rather than a variable potentiometer so check that's ok with your trusty multimeter, the wiper may have come off the shaft & got stuck.
Apparently simple circuits can be surprisingly hard to trouble shoot- occasionally Ive resorted to replacing all the components in one go! Check also for pcb cracks & dry joints especially around hot components. Failing that there's some cheap ready made replacement modules on ebay you might be able to fit in the space, search for eg ac motor speed controller

 

If you've replaced the faulty transistor and the fault is still there check the replacement to see if that is now shorted as well. If it has then there must be a fault causing that so look closely at the components connected to it. It might be worth replacing the triac even if it measures ok just in case. Is there a number on the ic in the background? If so see if you can find a data sheet & check it's supply voltage (dont forget the board has mains voltages on it). The power supply is probably directly from the mains via a capacitor and/or resistor, limited by a zenner diode- check the voltage across the zenner. Also the controller seems to be a multiway switch rather than a variable potentiometer so check that's ok with your trusty multimeter, the wiper may have come off the shaft & got stuck.
Apparently simple circuits can be surprisingly hard to trouble shoot- occasionally Ive resorted to replacing all the components in one go! Check also for pcb cracks & dry joints especially around hot components. Failing that there's some cheap ready made replacement modules on ebay you might be able to fit in the space, search for eg ac motor speed controller

The IC had no number on it just a generic 14pin all component tests ok, i will check the multiway switch thank you.

 

You could try disconnecting the gate of the triac- if the motor still runs then its faulty. Also a google search for sm168-s1 produces several pictures, 1 of which is an ic that says either CD4000 or CD4008 on it, its not very clear

 

You could try disconnecting the gate of the triac- if the motor still runs then its faulty. Also a google search for sm168-s1 produces several pictures, 1 of which is an ic that says either CD4000 or CD4008 on it, its not very clear

Mine says nothing but i'm trying to draw the circuit diagram. To understand more this circuit. Thanks

 

When you the schematic drawn, post it

 

can you please help me with the schematic, beside is that coil a transformer, or just a noise filter?

 

Almost certainly just a noise filter in series with the mains live in, so it should have just 2 connections

 

It is just possible that the toroidal inductor could be a pulse transformet to trigger the triac. But we will not know until we see the schematic you draw.

Les.

 

Good point! Tho I don't think there's a connection between it and what is probably the gate of the triac as far as I can see on the original pics posted of the pcb

 

Hi friends, sorry i just finished the diagram for this circuit, please help identify this IC component.

 

this is an updated diagram, please help