This control board is used in a variety of Siemens / Neff cooker hood products and eventually becomes intermittent - power cut offs, dead for varying periods etc as documented here http://www.elektronik-kompendium.de/...all&order=time in German.
The principle suspect is the NPN transistor which is part of the supply, but the intermittance suggests that it may be related to supply voltage variations or noise, as the power supply voltage to the microprecessor is on the high side ( >5.5V ). This transistor is ringed in the attached photo of the board before repair, and the solder appears to show signs of being hot.
The smoothing capacitor was a samwha 370uF, 25v which seemed low. It was not bad. After changing the smoothing cap to a 1000uF, 35v and replacing the transistor with the same version, all intermittents and power outs have stopped. Unfortunately, it is not possible to confirm which replacement cured the problem, or even if it was both, but the transistor certainly runs cooler now.
Hope this may be of use to someone
The principle suspect is the NPN transistor which is part of the supply, but the intermittance suggests that it may be related to supply voltage variations or noise, as the power supply voltage to the microprecessor is on the high side ( >5.5V ). This transistor is ringed in the attached photo of the board before repair, and the solder appears to show signs of being hot.
The smoothing capacitor was a samwha 370uF, 25v which seemed low. It was not bad. After changing the smoothing cap to a 1000uF, 35v and replacing the transistor with the same version, all intermittents and power outs have stopped. Unfortunately, it is not possible to confirm which replacement cured the problem, or even if it was both, but the transistor certainly runs cooler now.
Hope this may be of use to someone
Attached Files