ikea bekant electric table power supply repair

[RolandK]

My ikea bekant electric table power supply had the folliwing error:

It only moved 1 cm / a half inch, when pressing up or down.

Reason: to move the table, the power supply changes the voltage from 24V to 35V.

The used controller TEA1716 has a control loop supervision. While changing the Voltage the control loop supervision switches the power supply off.

Adding a little Offset Current to the Opto Coupler helps. The blue Resistor is 47k || 330k. 47k alone or 33k work too.

The control loop supervision is no more functional after the modification.

As always: unplug the power cord when working at the supply. Only do this, when you are experienced with high voltage equipment and know, what you do. Electricity can cause injury or death.

[RolandK]

As somebody asked:
The added resistor makes a non-zero offset current in the optocoupler. Now the input voltage of the regulator ic stays within the limit of the open loop supervision.

To get more load from the regulator, the current through the optocoupler is reduced. If the current is to small for a long time, the regulator ic asumes that the loop is broken and stops working to prevent an overvoltage situation and restarts after some time. The added offset current helps to stay on. But if the offset current is to big, you get not enought load.