Electronics > Repair

Inverter drive module overvolt fault

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Eamon:
This is what I can determine the circuitry feeding pin 9 looks like:


Not sure exactly what "D5" is, it has "HA7" written on it (no luck find the part on google) and it looks like this:

I've drawn it as a regular diode and assumed the polarity because the opposite makes less sense but not sure of the purpose of it, is it just to prevent pin 9 going -ve or is it actually a zenner diode to prevent too high a voltage on pin 9?

Anyway, I put this into LTSpice and it corresponds with the measured voltage at pin 9 and it shows 706.40177µA through R44 (not sure of the input impedance of pin 9).

The analog discovery 2 has a power supply capability between 0.5v and 5v in 0.001v increments so I'm hoping I can use that?  Not sure how to determine what its output impedance is though?

shakalnokturn:
Maybe worth checking C53A.

Eamon:

--- Quote from: shakalnokturn on November 07, 2022, 12:18:28 am ---Maybe worth checking C53A.

--- End quote ---
For short? (Pretty confident it's not shorted) or do you mean to check that it's value matches what the label says?  I was hoping to go as far as I could without needing to de-solder anything first.

shakalnokturn:
I'm expecting a low value. This capacitor gets some harsh current spikes when the PFC is active. MKP capacitors tend to degrade by slowly loosing capacity. A value too low could cause more switching noise to reach the MCU's "AC" sense.
If you must desolder use an iron with sufficient power.

Edit: If desoldering is a problem, for testing you could add a 2.2μF parallel to the existing one see if it makes any difference.

Eamon:
I can confirm that Pin 9 is the direct input for the "AC Plate voltage" value.  I connected my analog discovery 2 power supply to the end of the 150k resistor chain and varied the voltage observing the effect on the "AC Plate voltage", sure enough as I varied the voltage, the reported AC voltage varied between a floor value of 190v (at 1.83v or lower) up to a 255v ceiling (2.45v or higher)


--- Quote from: shakalnokturn on November 07, 2022, 06:25:04 am ---I'm expecting a low value. This capacitor gets some harsh current spikes when the PFC is active. MKP capacitors tend to degrade by slowly loosing capacity. A value too low could cause more switching noise to reach the MCU's "AC" sense.
If you must desolder use an iron with sufficient power.

Edit: If desoldering is a problem, for testing you could add a 2.2μF parallel to the existing one see if it makes any difference.

--- End quote ---

Thanks, I think I'll try that first as my de-soldering skills leave a lot to be desired :).  Now to source a suitably rated capacitor.
This is the existing one:
Not sure where I previously determined that it was 2.2uF but will need to verify that before I can try another in parallel.  But that part number seems hard to find any datasheet for best I've found is this link https://world.taobao.com/item/585823361132.htm?spm=a21wu.24122187-tw.recommend-goods.6 which has a picture with the same markings on it and says it's 2.2uF.  Does that seem like a reasonable value for such a capacitor?

Edit: the "G>" symbol on the capacitor suggests its from "Xiamen Faratronic Co. Ltd" and that took me to http://files.faratronic.com/book/2022/C35-1.pdf which I think means that it is in fact a 2.2uF 630v Metallized polypropylene film capacitor

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