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Repairing the Proxxon LHW rectifier PCB
Last updated on Sep 2, 2026
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Introduction
Go to step 1 ↓The rectifier IC on this PCB often fails. There may be a pop, some smoke, and the machine stops working. It is possible that the motor is damaged and destroyed the PCB as a result, but if you are lucky, only the PCB is defective. You can replace the entire unit, but it is cheaper to replace the rectifier itself. The PCB is labeled Proxxon 28547-28 or 28547-28B. The rectifier is type DB155S. It does not cost much and is quite easy to find. It is an SMD type, meaning it is soldered to the surface. However, the PCB has plenty of space, so it is not a major problem in this case.
What you need
Tools
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Two types of the PCB are shown here. Both can be used.
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These PCBs are for the device without cruise control.
Ask FixBot
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Remove the four very long Torx T10 screws next to the power cable that hold the device together.
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Pull the device apart until four parts are visible:
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Power connector with power switch
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Rectifier board
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Motor
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Drive
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Desolder the two power cables.
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Desolder the two motor cables.
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Image 2 shows a rectified PCB that has already been repaired. Two additional wires were soldered on because the conductive tracks had partially flaked off. You can also use a new PCB.
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You have likely already noticed the defective bridge rectifier IC, as some of the pins have flaked off. It is a DB155S type SMD bridge rectifier. It is quite easily available and inexpensive.
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The bridge rectifier is additionally glued in place, which helps to dissipate heat better. You could potentially use a thermal pad.
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Desolder the four pins:
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Two for the alternating current (AC)
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Two for the direct current (DC)
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Positive leads to the red motor wire
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Negative leads to the black motor wire
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On this PCB, the traces were partially chipped off and were replaced with small wires.
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Use a multimeter to check if all connections are soldered correctly. You can find information about bridge rectifiers here. You can test a rectifier by checking the continuity of the four diodes.
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Follow the steps in reverse order to reassemble your device.
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