LDU Overcurrent - Items to Check

[Mitchy]

Writing a post to summarize some of my own troubleshooting with regards to a V5 LDU board starting for the first time.
Not sure the root cause of the issues, other than the fixes performed.

The core take away from this is that I know the forum has many instances of Overcurrent alarms, and we're all normalized to think inverter failure; But after some initial troubleshooting it *may* just be a issue with the Current Sense/Overcurrent alarm circuit in some of these cases

After following the latest video from Damien on safely starting up the LDU, and my inverter passing all diode tests (and otherwise being in good condition) I went ahead to attempt the first spin.
Upon trying to run, I was immediately greeted with OVERCURRENT and HICUROFS1 errors, with no rotation.

Read the forum posts, which lead me to measure the voltage into U10
Confirmed several of the IC pins had low voltage (~3V) rather than the ~5V expected
After confirming my connector soldering was good, began to probe around the board, Ended up measuring at the associated Vias just upstream from the U10 pins confirming 5V.
Removed board, inspected U10 with definite cold solder joints on pins 1-4. Re-soldered the IC pins (and a few others on the board) and re-installed.

Attempted restart. Overcurrent errors have been resolved, but HICUROFS1 remained.
Graphed il1 & il2, il2 was responding to general noise and initial current, but il1 was flat/zero.

Measured voltage on the Test Points near the lower right of the PCB. Voltage for il1 and il2 was 2.3 & 2.6 volts respectively.
Continued to test the TPs nearer to the center of the board (around IC11) One channel was reading 1.8 V while the other was at 860 mV.
Started probing the board on the bench, having two identical circuits made comparing measurements pretty easy.

Measured 6.9 Mohm across R56, while the il2 partner resistor R49 measured 910 ohm.
Removed R56, measured and confirmed open circuit.
Replaced with a harvested 1Kohm resistor. Not ideal but it did let me spin the motor with minimal impact to the current reading offset.

Successfully rotated the motor (after swapping the encoder A/B wires )

[johu]

Thanks for the research on this.

The cold joints on U10/IC10 could be my fault, did it look hand soldered? During the chip crisis I had to fit various parts myself. Measured ok with the multimeter but apparently came loose then.

A dead resistor - that is unusual! Glad you discovered this, it should help others. Normally I measure the resulting voltages that go to the STM32. Maybe I missed it or it went bad afterwards - rather unlikely.

Will pin your post

[Skudak]

I have been fighting an overcurrent issue for 3 days now and am at a standstill. Would love any suggestions on what I might be missing

I had a motor that was running great with a ldu board. Unrelated to the board, the contactors opened under regen and fried the motor.

I moved the board to a new motor and now can't get around the overcurrent issue.

The motor will precharge, but once I click start (In neutral), it throws overcurrent immediately, sometimes it'll flash a THROTTLE1 error before an OVERCURRENT. I would think that if it was a short or something, it would blow my precharge resistor.

I have gotten the same result with another motor as well (2 motors which should both be good). That second motor I have not connected to HV yet at all and have done all my tests with just the low voltage harness.

I have tried a second ldu board that is untested and I assembled years ago (v4b) which gives the same error

I have tried all combinations of the two boards and two motors. I still get overcurrent with no HV

I have tried the latest firmware which instead gives a DESAT error instead of an overcurrent error. I downgraded back to 4.97 since that's what was running stable for me and is stable in my other car for years

I have plugged the 23 pin from a car currently running fine into the motors (to test is maybe my LV harness was an issue), still overcurrent with no HV

I have tried positive and negative ocurlimits

I ran the diode test and both motors test fine, I even confirmed on my bad motor that the test was being done correctly

I checked R56 on the boards and it measured fine

with HV I see the same thing as OP when I map the IL spot numbers, just noise.

I have a fourth motor in another car that is going to be very difficult to get out but I know it was working when I parked the car years ago, along with a fifth motor that is currently running a v4b board perfectly fine I could swap in one of these other boards. My fear is maybe the boards are causing irreversible issues to the motors and I would brick a perfectly running car. I'd really like to exhaust any other options first.

[Skudak]

Ok I just swapped the inverter board from the running car into one of these motors and the OVERCURRENT still persists with no power hooked up. Is there anything else I can test on the motors? I find it really hard to believe both of them are dead...

[johu]

Checked U10 voltages as stated above? All 6 desat signals go there.
Newer firmware tries to differentiate between window overcurrent and gate driver desat

[P.S.Mangelsdorf]

I moved the board to a new motor and now can't get around the overcurrent issue.

The motor will precharge, but once I click start (In neutral), it throws overcurrent immediately, sometimes it'll flash a THROTTLE1 error before an OVERCURRENT. I would think that if it was a short or something, it would blow my precharge resistor.

I have gotten the same result with another motor as well (2 motors which should both be good). That second motor I have not connected to HV yet at all and have done all my tests with just the low voltage harness.

I have tried a second ldu board that is untested and I assembled years ago (v4b) which gives the same error

.....
I have a fourth motor in another car that is going to be very difficult to get out but I know it was working when I parked the car years ago, along with a fifth motor that is currently running a v4b board perfectly fine I could swap in one of these other boards. My fear is maybe the boards are causing irreversible issues to the motors and I would brick a perfectly running car. I'd really like to exhaust any other options first.

Are you testing all of these in the same car/with the same set of contactors? It seems to me that, if you've tried multiple combinations of motors and control boards, the issue may lie with the contactors.

Have you done a continuity test to confirm that one or more is not welded?