EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: ScottM on January 10, 2018, 05:09:16 pm
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I am doing a repair to an I/O board in an ECU from a Volvo excavator and need some guidance on replacing /selecting a destroyed 3 terminal pass thru filter capacitor. I'll admit I'm pushing my abilities but have little choice as replacement boards are not available and I can't justify $2000 for a used unit that might work.
So here is what I know. The ECU is an old Contronic E system and the I/O board burned a 3 terminal cap on a circuit that is the 0V point for 5 different sensors. The first component is an 1806 size 3 termianl capacitor. It was literally burned off the board. This is a 6 layer board. I do not believe the damage went below the 2 layer. I am finishing repairs and replacing the missing pad but need help selecting a replacement capacitor.
What I know is that of the 5 sensors that use this path 2 provide a variable resistance, 2 provide a variable voltage and 1 is a 4-20ma circuit. I believe the damage occurred when the oil pressure sensor which is powered with 24V was disconnected and a connection was made from unfused 24V to this 0v path. I think. I have bench tested all the sensors and am replacing the 4-20ma one as it is not consistent.
There was another capacitor right next to this that provides an 8.5v source for the 4-20ma sensor that I will also replace. out of the circuit it measures 22Kpf. The closest I can find in that package is 33Kpf rated 300ma at 100V. Is this OK and would it seem appropriate for both replacements? Other ideas?
Any thoughts are helpful. Thanks.
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These are for EMI filtering, and try act as a fuse if a ground fault occurs... :palm:
Usually 1800pF-4700pF at 100-250V, not too large capacitance for fast/high impedance signals like an O2 sensor.
Look at Murata NFM (https://www.murata.com/en-us/products/emc/emifil) feedthrough capacitors, EMI filter, and TDK (https://product.tdk.com/info/en/products/emc/emc/3tf/catalog.html) YFF series.
The SMT package size is large, which will narrow down your options.