openinverter forum

I own a shop and we rebuild 2012-2020 large drive units.

We replace bearings, do coolant deletes and replace seals.

I am looking for a complete test procedure for inverters or any ideas on how to test them and possibly repair.

Tests that I currently do: (feel free to correct my readings if you think I am wrong)

- complete drive unit isolation over 4MOhms (max I got is 5MOhms)
- stator isolation test (3 phases disconnected from inverter). I am for a min of 67MOhms which will give 4MOhms when the unit is assembled and a goal of 550 on the stator after cleaning and drying in the oven.
- inverter isolation of 5MOhms when installed on the drive unit but with 3 phases disconnected from the stator.

- inverter diode test. HV positive to phase and HV negative to phase of 0.45v-0.7v and OL when flipping the DMM test leads.
- diode test per inverter phase with the HV sensing board removed, separating the 3 phases. I expect 0.3V-0.35V on each terminal one way and OL when flipping the DMM test leads.
On this test I usually see the voltage build up when testing in reverse from zero to about 6.5 and then it goes OL. Not sure if that is the way it should be or immediately go to OL. Maybe someone can shed some light on this.

If those tests pass then I conclude that the parts of the drive unit are good and I assemble it and install in the car.

I have 3 questions.

1. Are there any other tests that can be done?

2. Has anyone successfully replaced one bad phase from an inverter with a good one?

3. Is there anyone that repair phases with bad IGBTS?

Zoti wrote: ↑Mon Feb 16, 2026 1:06 am 2. Has anyone successfully replaced one bad phase from an inverter with a good one?

Yes. At least with the Open Inverter control board, the inverter is very tolerant of this. No idea if the stock control board would have an issue.

Zoti wrote: ↑Mon Feb 16, 2026 1:06 am 3. Is there anyone that repair phases with bad IGBTS?

I don't know if there's someone out there that does, but from my experience attempting this, it is far more of a pain than it's worth. Those things are BURIED under the control boards, bus bars, etc. You need a really high power tool to get the bur bars desoldered from the IGBTs, and you can't get to half of them until you remove the bus bars. That's not to mention the utter mess that the goo causes.

Right now we repair them for use back on the original vehicle but I am looking at using a Tesla motor in the future for a VW classic conversion.