90% of failures in the operation of this engine, installed on cars of OPEL, Astra G brands, are related to the failure of this unit and the appearance of error 0251. Very often, error 0251 is not recorded in the memory of the main engine control unit. Also, often, after a short cooling of the engine, it starts again and works without any complaints. Now, many have “learned”, allegedly, to repair these blocks, simply by opening the lid and soldering cold rations on the power elements on the board. As a rule, such a “repair” helps for a short time and soon the unit fails much more seriously. Yes, sometimes this repair helps, but not always. I repair the block myself only with complete disassembly of the block for many reasons.
Here is the soldered contact from the inside.
The main cause of failures is the drying or non-contacting of the leads of an electrolytic capacitor (1500 microfarad, 35 volts). As a result, there is a shortage of power at the peak of the pulse, overheating and failure of the transistors of the converter occur. I didn’t find dried capacitors during the test, so I don’t change them
The second reason for failures is the failure of the stabilizer (9 volts, type 7809 (KREN8A) 1.5 Amperes). This stabilizer is the source of the bias of the field-effect transistors of the converter and the modulator (MOSFET). Instead of the minimum allowable voltage in this circuit, equal to 8.6 volts, there remain 7-8 volts, which leads to incomplete opening of the transistors, displacement from the operating point, their overheating, appearance of some signal harmonics, etc. Also, if there is 8.6 volts at the output, this still does not mean anything – the stabilizer may not hold the load. As a result, the block first overheats and “goes into the spacing”, and after the spacing, both the transistors and the rectifier diode, the elements of the operating system (the first is a powerful SMD resistor 0.02 Ohm) and stabilization often fail. The burning of the findings of the high-voltage choke is caused by these reasons. The circuit provides protection against the failure of the 9-volt stabilizer, but in most cases it is not effective. The protection is implemented as follows – from the 9 volt source there is also power supply to the 5 volt stabilizer – 78M05, which serves to power the comparators of the converter and the logic circuits of the modulator. The idea of the developers was as follows: when the reference voltage of 9 volts disappears, 5 volts also disappears and the unit simply does not turn on, the transistors do not heat up and the motor simply does not work. But for powering 78M05, 6 volts is enough, and even less – 5.5!
No matter how many blocks were disassembled, almost all were with defective stabilizers. The stabilizer must stabilize the voltage without load and with load.
Check the repaired unit without load and see the following:
Now I connect a small load in the form of two coolers
And here’s another
Change to new
This is a new one.
When dismantling, pay attention to the winding contacts of the choke, to which the winding pins are soldered. Overheating may cause no contact – cold soldering. Both of these contacts must be soldered, no matter how beautiful they look!
Add a safety jumper
Clean the burning holes with a toothbrush and solvent
Remove unnecessary pins
Perhaps this information will be useful.