Reparasi Power Stage / werstan AC Volvo 850

I finally received the transistors and I will describe here the procedure to fix the blower power stage:

1- remove the power stage from the car (I found removing the metal knee bolster makes this very easier)

2- Open the case. It is stuck together by some plastic clips. Pry them out.

3- Unsolder the transistor. It is positioned a way that you have to unsolder it before taking the circuit board apart. I used some solder wick for that step.

4- Unscrew the circuit board from the case and set it apart

5- Now you see the transistor in all its glory. Unscrew it from the heat dissipator. Be careful, this screw may be stuck hard due to corrosion between the screw and the aluminum dissipator (same issue as the 240 'falling bumper' problem)

6- Apply a dab of dielectric grease where the old transistor was in contact with the dissipator

7- Screw the new transistor, flat side down, as the old one was.

8- Reinstall the circuit board, making sure the transistor legs inserts through the 3 holes you unsoldered. If the new transistor is screwed the same way than the old one, don't bother with the polarity, the legs order is standard for all transistors.

9- Solder the new transistor

10- re-screw the board and close the case

11- Go test it on your car, I recommend you test it with the dissipator fully inserted in the air duct, for proper cooling.

The transistor I used: STP140NF55
The original part: 2SK1423

The form factor you HAVE to specify for your new transistor: TO-3p
(if not, it will not fit properly and you will have to rework the connections, what I had to do with my TO-220 transistors.

I drove the car 2 hours today, 31C outside, humidex 38C, A/C full blast and the repair worked well. So, I would say that it is feasible to repair it yourself.

The picture is a TO-3p form factor. I think it is the size you have to specify to make the rebluid an easier task.

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