Repair a Gaggenau/Bosh Oven Power Supply


July 1, 2015


How to save money and enjoy diy!

If the power supply of your Gaggenau/Bosh oven with serial code YL 135 T85 failed, you can exchange it with a standard industrial power supply instead to buy an expensive spare. Such model are less expensive and more robust.

Warning: You must have some electronic knowledges to achieve this. And of course take care to electric hazards!

This power supply is common to several Bosh ovens. It is a switching power supply rated at 9.6 V and 12.5 W. But there is a trick, since they added a zero crossing circuit on the board. This function is implemented using a voltage divider, an optocoupler and two transitors mounted in darlington powered by the 9.6 V rail.

In general it makes no sense to try to fix a standard switching power supply. In our case the driver chip don't have public datasheet on the net. So no way for this price.

First check the output voltage of the power supply. If the power supply is dead then you can buy a compatible power supply like a TDK-Lambda HWS30A-12/A model. The power supply must have a variable output voltage (for the funny 9.6 V) and the same power. Also think to the temperature during pyrolysis.

You can plug temporally a laboratory power supply to check the oven is operational before to buy a new power supply.

Next you will have to unsolder some devices on the circuit to unplug properly the power supply part and connect your new power supply to the corresponding traces. It should be easy for you if you are able to achieve this reparation.

You can check the zero crossing is well functioning using a frequency counter, it should report a square 50 Hz signal.

For information, there is three boards on this oven:

  • a 9.6 V power supply / zero crossing board,
  • a main board with a plenty of relays and other stuffs,
  • an interface board with the front LCD.

Both boards have a microcontrollers and communicate by a serial bus.

Have a good hack!

Photo of the power supply electronic board (recto)