Schubart Inverter 3KVA (Axpert Clone) Error Code 09

[CharlesFoster]

hi Guys

So my inverter started giving error code 09. As per all the forums and advice i started first with the IGBT's. They are all fine.
The mosfets are all fine, diodes all fine. caps are fine.
I could not find a single part faulty yet.

The schematic i have differs a bit from my unit, so difficult to follow all the places to check.

Any body that has a better schematic or even advise were to check further?

Axpert MKS 1-3KVA Service manual 20130611.pdf

[Coulomb]

8 hours ago, CharlesFoster said:

or even advise were to check further?

Perhaps check the bus voltage, to see if the bus soft start circuit is working. You might be able to access the bus voltage from above the PCB.

[CharlesFoster]

Starts off on 0 and climbs to 3.5v before E09. if i restart the process it climbs about another 2v. I have checked UC3845 supply, 15V is there. i get 1V on the FET gate, so i think it is not switching. i measured resistance on UC3845, pin 7-5 42K and 6-5 32K but still think it is blown. Diodes around the circuit tests fine. Also added picture of circuit in question.

Edited October 21, 2020 by CharlesFoster
Attached picture

[Coulomb]

On 2020/10/21 at 5:23 PM, CharlesFoster said:

i get 1V on the FET gate, so i think it is not switching.

Can you measure the frequency of the gate signal? It may be pulsing, with an average or RMS (depending on your multimeter) of 1 V.

Quote

i measured resistance on UC3845, pin 7-5 42K and 6-5 32K but still think it is blown.

Resistance measurements are pretty useless, but that's what is typically in a service manual. Can you measure 5.0 V on Vref? (Pin 8 wrt pin 5). That's a functional test. If it's totally blown up, you would not expect to see 5.0 V on Vref.

Also, do you see any voltage on pin 3 (Isense) wrt pin 5? If the FET is conducting, you should see a small voltage there. If the FET doesn't conduct at all due to no gate drive, that voltage would be zero.

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Also added picture of circuit in question.

Is the "transformer" involved the tall yellow one in the bottom right of the photo? There don't seem to be enough "transformers" on the main board. The Axperts use them for gate isolation, power supplies, etc. The large transformer and heatsinked FET seem more appropriate for the main power supply. On the Axpert's bus soft start circuit, both the FET and the output diode have no heatsink.

[CharlesFoster]

hi,

Thank you for the reply.
I do not have a scope to measure the frequency, but tried with the DMM(i have a Toptronic / Brymen TBM805), i get 52khz stable.
As for the voltages, vRef - 5V and iSense is 80mV.
Yes, the yellow transformer bottom right hand is the one involved in soft start.
From what i could deduce:
The top part with large transformer(above heat-sink) is the main PSU / Inverter. Lets say high voltage side.
Below heat-sink is the battery charger and DC-DC soft start.
Heat-sink with encapsulated toroids seems to be the solar parts.
The heatsink has all the IGBT, Diodes, bridge and FET's on. All tested(circuit / functional testing, not DMM) and working

[Coulomb]

14 minutes ago, CharlesFoster said:

i get 52khz stable.

That seems reasonable.

Quote

As for the voltages, vRef - 5V and iSense is 80mV.

Those seem good too. Isense is low, but that's quite probably because it's not doing much (not providing much power).

Quote

The top part with large transformer(above heat-sink) is the main PSU / Inverter. 

Ah, of course. It looks very different to Axperts.

Quote

Heat-sink with encapsulated toroids seems to be the solar parts.

The solar charge controller seems very Axpert-like.

Can you measure an AC voltage at the output of the transformer?

My guess now is that the soft start power supply is working, it just can't charge the bus capacitors because there is a load on the bus. Possibly damaged IGBTs.

If it's easy to pull out the diode at the output of the soft start circuit, do so and see if you get more AC voltage at the transformer output.

I'm being lazy and using the term "transformer" where technically these are multi-winding inductors, with an air gap in the magnetic path to store energy.

[CharlesFoster]

okay, so here is what i did and found.

I measured frequency on drain of FET, found 250khz that seems very strange but okay, i left it there for now.

I removed the IGBT's in order to separate the high current 400v from the soft start. Voltage on 400v caps still below 3v.

I removed the 400v caps, tested them, they seem fine and within tolerance. 480uF and 510uF.

The thing i can not find is the link between the diode and the caps. i find 2 little isolation transformers going to IGBT's but no direct link to the cap, on either positive or negative. so i assume there is something in between that i need to find first. schematic would really help about now.

I in fact not 100% sure i have the right diode where i measure, although on the output of the transformer.

[CharlesFoster]

Another follow up. Seems Diode D1 as per image does not go to the 400V. Disconnecting it also made me fry the comms board. don;t use it, so no harm...yet.
From the TX1 one side goes to R31 resistor, then D2 diode, into U15(79L12 regulator.) I have not tested output on regulator yet, but seems futile since it can not be my 400V then.

So, it actually looks like this is not my soft start circuit then at all, but rather some small DC-DC psu.

I am going to try and trace back from the caps and see if i can find the soft start.

[CharlesFoster]

okay, sorry....big mistake. that is the SPS circuit i am busy with, not soft start. So starting over again.

[NZGuyCHCH]

Hi,  Just wondering if you had any luck fixing this board.

I have the same inverter that I purchased secondhand. That currently does not detect the 230V line in voltage.

The rest of the inverter works fine.

I am trying to fix it slowly but surely. Happy to make some simple voltage checks for you if needed, while I have everything in pieces.

Cheers

[CharlesFoster]

After replacing almost everything i got it working. This inverter works different than the other brands. soft start is purely switching one fet on, and then the rest for high current.You will see on the PCB one fet on the bank is driven by a separate IC.

So in your case i would start with the bank (in my case with 2 heat sinks) check those fets and drivers. I saw the resistors burnt as well once those banks were off, so i replaced the drivers, the resistors and the fets.
Mine is not 100% yet as it trips above 10% usage now, but seems to be a current sense circuit.

I have to take it apart and check further.

[Coulomb]

1 hour ago, CharlesFoster said:

This inverter works different than the other brands. soft start is purely switching one fet on, and then the rest for high current.You will see on the PCB one fet on the bank is driven by a separate IC.

Interesting. They seem to have copied 80% of the Axpert design, and decided to change the soft start circuit. Perhaps they feel it sounds better in court if there are some differences they can point to.