iOnico
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Re: Troubleshooting and repair for On-board Charger (OBC)

Wed Jun 09, 2021 3:25 pm

OK, I went on with testing the ICs out of the category “others”:
Others:
74VHC123A, Multivibrator, IC#: 505,706 Vcc pin16
ST95320W, eeprom, IC#: 508 Vcc pin8
TJA1050, CAN Transceiver, IC#: 704 Vcc pin3
JRC2746, Dual OpAmp, IC#: 515 Vcc pin8


After having disconnected all these ICs I’m now reading a resistance of 774 Ω from 5V to Ground and of 674 Ω when switching the leads.
The resistance ranking of the ICs so far is (in ascending order):
IC503: 20 Ω
IC502: 23 Ω
IC506: 33 Ω
IC518: 52 Ω
IC504: 56 Ω
IC704: 62 Ω
IC505: 91 Ω
IC716: 356 Ω
IC508: 735 Ω
IC706: 66.5 kΩ (or 60 kΩ when switching the leads)
IC515: OL (or 20 MΩ when switching the leads)
IC705 and IC717 are particular: they show a strange behaviour as reading won’t get stable: during minutes, measured resistance will grow by 1-3 unit steps of the smallest digit displayed (1-3 Ω when meter display is showing kΩs, 1-3 kΩ when meter diplay is showing MΩs). I stopped the measurement on IC705 after several minutes of watching the figure go up from around 1 MΩ to 2.3 MΩ (and from around 240 kΩ to 760 kΩ after having switched the leads) although the figures hadn’t settled. The growing reading is to observe independently of the sense of the measurement (leads switched or not) and on all reproduced measurements. The same is for IC717: no stable reading came out, resistance was at least 240 kΩ before starting growing. So, these chips won’t have participated to the short, but they are doing strange things. You may be surprised that these findings are not in line with what I had written in my last post: I realized when measuring today that on the measures taken last time, I had contact to the 5V circuit (my lead was touching the disconnected VCC contact of the IC but also the solder pad of the 5V supply from which it had been disconnected). The around 60 kΩ of resistance I had measured were between the 5V solder pad and Ground. I’m finding these same resistance values also when I’m touching with the leads the capacitors next to the VCC pins of IC717 (C857) or of IC705 (C818) and measure against Ground.

And the same information as readings included into the pictures:
Image

Image


I don’t want to be too optimistic, and some expert opinion will be very welcome to interpret these findings. The resistance values from 5V to Ground (and vice versa) are now higher than those that Kenny had measured on his boards. To me, this looks as if the devices creating the short have now been disconnected and the board could have not too bad chances to work correctly again if the devices having a resistance of less than 1kΩ (IC503-IC508 according to the order of the list above) would be replaced. I don’t know at all what I should think about IC705 and IC717. I don’t know if the observations made on them are part of a normal behaviour, if it’s a sign of damage of the ICs or if it could be a sign of even more trouble somewhere in the circuit around these two ICs.

This is too much of an open end for me so @kiev I’ll contact you via PM concerning the board you have. Would be great if this could be the solution!

kiev
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Re: Troubleshooting and repair for On-board Charger (OBC)

Thu Jun 10, 2021 4:29 pm

i don't have any loose parts to check for comparison, but i might just order up a batch to have on hand for this sort of thing and to do repairs.

The goofiness of the 2 out of 3 Hex inverters, 74VHC14, may be due to internal circuits of the chip when it is not damaged. The meter response seems like it is charging up a capacitor somewhere.

The parts cost would not be high, and you could take it to an electronics repair shop that can do surface mount soldering to replace the chips.

Probably the 12V to 5V power supply should be checked before going too far down the repair path, but it is definitely looking hopeful.
kiev = kenny's innovative electric vehicle

coulomb
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Re: Troubleshooting and repair for On-board Charger (OBC)

Sat Jun 12, 2021 4:35 am

kiev wrote: The meter response seems like it is charging up a capacitor somewhere.

Agreed. Those are possibly op-amps or similar with dual power supplies (e.g. ±5 V); a low resistance from +5 V to -5 V supply pins would cause the meter to be reading the capacitor on the -5 V rail. For those, it's best to lift the two leads for power supplies, and test from one lifted lead to the other instead of the one lifted lead and ground.

iOnico
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Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Jun 13, 2021 4:56 pm

Thanks for your interpretations of my findings. I had another look into the datasheet of 74VHC14FT (the goofy IC705 and IC717) to determine another pin to desolder. The device is described as being a Hex Schmitt Inverter.
Besides the VCC and Ground pins there are only 6 logic IN and 6 logic OUT pins on the device. There isn't anything really looking like a second power supply... Another idea how to troubleshoot these ICs?

How would you proceed to test the ICs out of the "power supply ICs" group? That would be the last ones out of Kenny's list that still remain to be tested...
Power Supply ICs would use a different technique to troubleshoot
JRC2374, PWM DC/DC Regulator, IC#: 707, 708
MO33, 3.3 supply chip, IC 718
TACQ, Voltage regulator chip, IC513

coulomb
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Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Jun 13, 2021 5:24 pm

The goofiness is all mine. I didn't realise that you'd already determined these to be hex Schmidt inverters. So definitely not dual supply op-amps. Sigh.

Sorry for the bad steer.

Edit: as for testing, they are inverters, so a low voltage at an input should translate to a high (very nearly equal to the pin 14 power supply) at the output. Similarly a high input should produce a low output. Medium voltages (between roughly one third and two thirds of Vcc) will end up high or low, but should be stable, because of the Schmidt trigger hysteresis.

To test one, solder bridge its Vcc to the board again and power with 3.5V or so (maybe 5V now that most of the short circuit is gone). That might give you the confidence to assume for now that they don't need replacing.

kiev
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Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Jun 13, 2021 6:03 pm

For the Hex inverters, now lift the ground pin and then check the resistance from the Vcc to ground pin.

It is possible that now you are seeing the variations due to contribution from capacitors. Before you removed the shorted parts, the low resistance of the short dominated the readings. That's just my guess to explain the meter readings.

Now that all the shorts are disconnected, retry your 2 to 5 volt testing and if possible measure your current--it should be much lower than before and nothing should be heating up. Also check the microcontroller ic701 for heating when you do this.

To check the power supply ics you will need to apply 12 V power and ground to the appropriate pins of the CN101 connector. Pin 12 is the switched 12V supply, and i measured about 30k Ohms from + to -, and when reversed. There is definitely some charging up of capacitors by the meter so it may not settle down. But if your board is not somewhat similar then don't apply power.

When you do apply power you will want to limit the current of the 12V to about 50 to 100mA. After the 12V has been connected then you can check the 5V supply to ground to see if it is being created, and if it is then check the 16V supply to ground.
kiev = kenny's innovative electric vehicle

iOnico
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Re: Troubleshooting and repair for On-board Charger (OBC)

Mon Jun 21, 2021 4:11 pm

During the weekend I did the tests you had suggested, to find out more about the health of the 3 hex inverters ICs and the power supply ICs creating the 5V and 16V power supply.

The test based on verifying the (inverting) reaction of the inverter ICs didn’t bring satisfying results. I supplied the 5V directly to the ICs Vcc leg, maybe I should have solder bridged it again, but I saw no good reason, why it should have changed the test result. These IC legs are so small and they are so close to each other and input and output of one circuit are always direct neighbours... Not to forget the varnish or glue that covers great parts of the board, including the IC legs, so you never know if you have good contact to your measuring object or not. I didn’t manage it well to contact the leads to supply the input to one and get the outgoing signal from the other, reading the meter at the same time. I haven’t been able to observe the behaviour I should have observed for these ICs, but as mentioned, this may also be due to my testing “technique”. My impression was that they didn’t work as they should.

I went on and desoldered the Ground leg of each of the 3 ICs. There the results are easier to interpret: I measured the following resistances from Vcc to Ground through the ICs:
IC705: 102 Ω
IC716: 249 Ω
IC717: OL
This time the values settled quickly, there was no effect of loading capacitors to observe.

The resistance values between 5V and Ground (and vice versa) haven’t been changed much by the desoldering of these 3 contacts:
5V -> Ground: 760 Ω (was 774 Ω before)
Ground -> 5V: 630 Ω (was 674 Ω before)

When supplying 5V to the 5V circuit, there is no element heating up particularly. The board as a whole gets a bit warmer, but there is no device standing out of the rest. With higher air temperature on the day of this test, compared to the days of the other temperature measurements I had done before, the measured temperatures this time stayed under 36°C, where they had been at over 40°C on the earlier tests. And this time I applied 5V, on the temperature test before it had been only 2.8 and 3.5 V.

Finally, I went on to the test of the power supply ICs and tried to create the 16V and 5V power supply out of the 12V power supply. I had verified before that the resistance from the 12V pin of IC101 to Ground was at around 30 kΩ. And yes, it was. The 16V is created. Voltage is even a bit higher, more around 16.5V. The 5V however is not created that nicely. There is definitively a stable voltage created, but it is of only 0.66V. I don’t know if the large number of disconnected ICs could be part of an explanation for this gap. The current pulled at the 12V didn’t get over 40mA.

So… that’s the news from my board. I just noticed that your last reply to me in this thread was your 1500th post, Kenny. Congratulations! Impressive figure!

kiev
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Re: Troubleshooting and repair for On-board Charger (OBC)

Mon Jun 21, 2021 4:37 pm

Haha, thanks i hadn't even noticed the number of posts.

Indeed the "16V" supply is actually higher and closer to 17, but nominally i just refer to it as the 16. But that is a good test result to prove certain portions are okay and working.

The 16 gets created from a boost PWM regulator chip from the 5V supply, so even though you found the 5V was pulled low somewhere, it is held up elsewhere sufficiently for that task.

i would guess that there is still some component(s) pulling down the 5V, maybe not a direct short that can be measured by Resistance readings, but gets turned on and then completes the path, such as transistor, diode, or a secondary supply such as 3.3V created from the 5V. e.g. IC718; ic512, 513; TR301, 706;

i really wonder about IC512 due to its proximity to the 5V line damaged up at the primary site. It is marked "TACQ" and i think it is a TI TL431 part number, precision reference voltage chip.
kiev = kenny's innovative electric vehicle

coulomb
Posts: 297
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Re: Troubleshooting and repair for On-board Charger (OBC)

Tue Jun 22, 2021 6:08 am

kiev wrote:i would guess that there is still some component(s) pulling down the 5V, maybe not a direct short that can be measured by Resistance readings, but gets turned on and then completes the path, such as transistor, ...

I would be more inclined at this point to think that something that was trying to supply 5 V into a near short circuit was damaged. The fact that you can run the 5 V circuit on actual 5 V now without excessive heating suggests that to me. So I'd look now at what generates that 5 V rail.

Edit: my guess is it's under the area of the board with all the inductors on it, beside the connector. I wonder if it's possible that one of the chips you disconnected from 5 V is needed to generate the 5 V rail? That sounds a bit silly as I type it. But maybe there is a check on the level of the 5 V rail, that you have disconnected, so now it thinks there is something really bad happening and is stopping the 5 V as a precaution.

kiev
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Re: Troubleshooting and repair for On-board Charger (OBC)

Tue Jun 22, 2021 7:11 am

coulomb wrote: But maybe there is a check on the level of the 5 V rail, that you have disconnected, so now it thinks there is something really bad happening and is stopping the 5 V as a precaution.


i think you are on the right track here. When i was tracing the DCDC board there were several circuits with the function to check and compare that the low level supply voltages were present and neither too low nor too high; And on the lower power board of the OBC there are circuits which sense and feedback low level voltages to the upper control board. So it makes sense and i would expect that there are some supervisory circuits such as related to the presence of the Hot All The Time (HATT) and the Switched 12V and 5V supplies.
kiev = kenny's innovative electric vehicle

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