Chainsaw ignition block repair. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Chainsaw ignition block repair. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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Nowadays, individual farms are increasingly using Ural-Electron and Druzhba-4-Electron chainsaws, the engines of which are equipped with an electronic ignition unit. This block is very simple in design, but, like other equipment, sometimes it fails. Replacing it with a new one is not a difficult task, but it is rarely on sale, especially in rural areas, and it costs a lot. A radio amateur is quite capable of repairing the unit.

The ignition unit of these chainsaws belongs to the class of unified contactless magnetos. Structurally, it is made in the form of a briquette of cured transparent epoxy compound, which is used to fill the assembly, which includes most of the parts of the block.

After the repair described below, the unit will become a thyristor-capacitor unit. Its scheme is widely known (see figure). From the previous unit, the high-voltage transformer T1, the generator coil L1, the ignition sensor coil L2 and the capacitor C1 were used.

Chainsaw ignition block repair

When the flywheel with magnets rotates, an alternating current with a voltage of about 1 V is induced in coil L400. It is rectified by diodes VD1, VD2. The pulsating voltage charges capacitor C1.

At a certain moment in the rotation period of the flywheel, a current pulse appears in sensor L2, which, passing through the diode VD3, opens the thyristor VS1. As a result, a discharge current pulse of capacitor C1 flows through the primary winding of the ignition coil T1, and a high voltage pulse appears in the secondary winding, causing a spark discharge in the spark plug in the engine cylinder.

There is no need to dismantle the used parts of the previous block - they remain in place. You just need to free their conclusions from the compound. This is not difficult to do, since the compound is transparent and not too hard, but you should work very carefully so as not to damage the leads and their insulation.

Diodes VD1 and VD2 are soldered directly to the freed terminals so that after installing the flywheel in place, it does not touch the parts and conductors. The VS1 thyristor and zener diode are installed on a small fiberglass or getinax strip and placed in a durable box of suitable dimensions. The box is secured with screws to the body of the chainsaw and connected to the block with three wires in reliable insulation. The wires are passed through three holes with a diameter of 4 mm, which must be drilled in the engine housing near the ignition unit.

Experiments have established that KU202N thyristors operate stably in winter conditions at temperatures down to -40 °C. Zener diode D815A can be replaced with D815B or D815V. Diodes - any from the KD105 series or others for forward current and reverse voltage of at least 100 mA and 400 V, respectively.

If you need to replace capacitor C1, then any paper or film capacitance of 0,5...1 µF for a voltage of at least 600 V will do instead.

The block does not require adjustment.

Author: P. Ivanov, Vilyuysk, Yakutia-Sakha

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