After an interesting discussion on the Home Barista forum about the possibility of a constant DC voltage causing electrolysis of the autofill probe I thought it would be a good idea to revisit the auto-fill circuitry.
When I repaired the GICAR in my machine, I looked fairly closely at the circuit. I took a few notes, but I didn't draw it completely. Looking back at the notes, what I did see was an AC transformer with two taps, marked as 15V and the other for 20V (these measured 19 and 27 VAC (with no load)). I'm pretty sure that the probe was connected after a rectifier and that a capacitor was used to provide hysteresis. I therefore assumed that there was a constant DC voltage going to the probe. However, I just took the cover off my machine at home and put a multi-meter on the probe. The readings are not conclusive. I see roughly +160mV which seems to drop occasionally, possibly below zero. I don't see AC, but this is on a 200V scale with a cheap digital meter... I'll bring home a better meter this evening. It seems pretty unlikely that there is 19V or 27V AC present though.
Here are the photos of the GICAR controller that I took way back when:
When I repaired the GICAR in my machine, I looked fairly closely at the circuit. I took a few notes, but I didn't draw it completely. Looking back at the notes, what I did see was an AC transformer with two taps, marked as 15V and the other for 20V (these measured 19 and 27 VAC (with no load)). I'm pretty sure that the probe was connected after a rectifier and that a capacitor was used to provide hysteresis. I therefore assumed that there was a constant DC voltage going to the probe. However, I just took the cover off my machine at home and put a multi-meter on the probe. The readings are not conclusive. I see roughly +160mV which seems to drop occasionally, possibly below zero. I don't see AC, but this is on a 200V scale with a cheap digital meter... I'll bring home a better meter this evening. It seems pretty unlikely that there is 19V or 27V AC present though.
Here are the photos of the GICAR controller that I took way back when:
Hi, I have the same controller. I just replaced the transformer on it but sadly still didn't switch on the auto fill function. now I don't hope its not the relay because that one is no where to be found. did you find a different way to make it work?
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