Hi folks,

I am suffering from a damaged Voltronic inverter having its Mosfet battery blown, I have replaced them all and I noticed the 10R resistors of Mosfets drivers are blown as well so I replaced them.

I am struggling with the 2SA1020 transistors value between Base and Collector, which indicates around 0.038V when using Diode mode.

I have suppressed these wrong values and tested it, it is working and outputs 230V but it is draining around 2.6 Amps with no Load, which is a weird consumption (usually it is about 1.6 Amps).

Please take a look at the screenshots attached for more details.

Can anyone have an idea why the PNP transistors are shortening? Knowing that all parts' values around are good.

Thanks

6 hours ago, Adnano said:

I have suppressed these wrong values and tested it, it is working and outputs 230V

? How are you suppressing the short? 

Are you saying that you replace the transistor and the good replacement immediately fails shorted? Yet the inverter still works, only with increased self consumption? 

6 hours ago, Adnano said:

Can anyone have an idea why the PNP transistors are shortening? Knowing that all parts' values around are good.

Does that include the SG3525?

The base to collector reads 0.038 V on diode range, what about resistance? If it's around 100Ω, it may be that one of the SG3525's outputs is shorted to -12 V. The DC-DC converter may operate in a degraded mode with only output working.

3 hours ago, Coulomb said:

How are you suppressing the short? 

I didn't do anything, just turned the inverter on.

 

3 hours ago, Coulomb said:

Are you saying that you replace the transistor and the good replacement immediately fails shorted? Yet the inverter still works, only with increased self consumption? 

No, I didn't replace them as they are good (I removed them all and the short still exists.

3 hours ago, Coulomb said:

Does that include the SG3525?

How come the SG3525 can affect these transistors? As both circuits are isolated from each other by transformers!

3 hours ago, Coulomb said:

The base to collector reads 0.038 V on diode range, what about resistance? If it's around 100Ω

Yeah it is around 21Ω

 

3 hours ago, Coulomb said:

it may be that one of the SG3525's outputs is shorted to -12 V

There is no short on SG3525 pins

On 2024/03/23 at 5:51 PM, Adnano said:

How come the SG3525 can affect these transistors?

If there is a short between output and "ground" (-12 V), then base to collector of the 2SA2010s you will see the resistance of the resistor between the bases and the outputs (100 Ω in most Axperts). Are these resistors perhaps 22Ω in this model?

What resistance do you see between the SG3525's pin 12 (-12 V) and either output (11 and 14)?

On 2024/03/23 at 5:51 PM, Adnano said:

As both circuits are isolated from each other by transformers!

Are we talking about the same circuit? I'm working on this part; your parts designators (e.g. Q47) may vary:

On Maxo's MKS 5K-48 schematic, Q47 is shown as 2SA2010. R273 and R247 are parts of interest; what is their marked value?

If you're talking about a different part of the circuit, please paste a screen dump.

Have you checked all 4 2SA2010s?

Do you have the equivalent of R271 below? It sems more likely that the equivalent of Q16 has gone to about 11Ω, resulting in the  21Ω that you see.

 

The part I am talking about differs from the one you are meaning.

I am talking about the circuit after the small transformers as below

I have checked the service manual of VMII and found out that the transistors are both PNP and the value between B and C pins is normal and should be 0.063V which is my case as well!

 

20 hours ago, Adnano said:

The part I am talking about differs from the one you are meaning.

Ah!

20 hours ago, Adnano said:

I have checked the service manual of VMII and found out that the transistors are both PNP

Actually, that part of the service manual is wrong. It makes no sense to have both sides PNP, and the 2SD1624 is an NPN transistor.

20 hours ago, Adnano said:

the value between B and C pins is normal and should be 0.063V which is my case as well!

That's quite strange. I can see no reason for a difference, and on a spare 5 kVA 4 kW board I have here, I measure the same ≈0.6 V (different polarity) on two pairs I checked.

I wonder if the machine they got their voltages from had the same fault as yours!? Is it possible that your 1 μF capacitors are low resistance? Mine read about 287 kΩ in one direction, megohms in the other.

I just run the inverter with the existing behavior and it seems it is working normally (charging and discharging)

17 hours ago, Adnano said:

I just run the inverter with the existing behaviour and it seems it is working normally (charging and discharging)

I think that's taking a huge risk. My guess is that you will eventually blow a set of MOSFETs.

I didn't found any justification for the values and I removed all components and replace them, and same result. It seems it is designed like that!