Introduction
If the "accelerator pedal" on your sewing machine no longer works properly, the capacitor or triac may be faulty. These instructions show you step by step how to replace these components to restore the functionality of your sewing machine and extend its service life.
Error : Overlock machine (Singer) only knows full throttle, no longer switches off.
Fault: Triac BT136 and possibly also one of the capacitors - gray, see picture - was defective and was also replaced.
With multimeter capacity was only approx. 1/10 of nominal value. (0.047μF = 47nF dropped to 15 nF).
For disassembly, see also the instructions for BT136 here under sewing machines.
ATTENTION : Such circuits without transformer use special capacitors. When replacing, make sure that any "X2" specifications or similar on the spare part also apply. It is about dielectric strength / voltage peaks in the 230V mains).
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Open the device. Compare with this wiki. You may have to look for the catches or the screws with which it is locked. On this model, the pedal is only engaged. Pay attention to the moving plate and the spring.
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Expose the circuit board so that you can reach the underside to desolder the components.
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This is the triac. Desolder its three legs on the underside. These instructions tell you how to check it. Replace it if necessary.
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Here are two capacitors. Read their capacitance. Desolder them and measure them with a suitable digital voltmeter. Replace them if necessary.
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Fuse. Measure its continuity and replace if necessary. Remember that a blown fuse usually has a reason.
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Position the new components (capacitor and triac) in the appropriate places on the circuit board and solder them in carefully.
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Verify the soldering points with a multimeter to ensure that all connections are correct and stable.
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Reassemble the accelerator pedal housing and reinstall the screws or catches.
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Function test: Connect the sewing machine and test the accelerator pedal to ensure that the new components are working correctly.
