Power Inverter for a Car (Diagnose + Repair)

[scampo77]

I found another thread on when googeling my problem, I posted on that website but there hasent been any responses. I have the exact same hardware but a different failure. It looks very similar in design to a car amplifier except just generating a modified square wave all day instead of music driving the outputs.

About repairing a 1750 watt power inverter

Mine is the same hardware but I don't seem to have any shorted transistors or diodes bolted to the heat sink. My hardware is identical to all of his pictures I just seem to have a different failure. I have the battery voltage appearing at the display and the red fault light on.

Symptoms,
I have no gate voltage to the IRF3205 but I have 15v drain
I have ground on the source + drain IRF640 and 15v on gate. It seems to be fully on.

All the ICs seem to be getting power I posted all of the pin outs from the control part. I am not too sure where to go from here. Any help would really be appreciated. I can post more voltage readings or more pictures if someone is willing to help me through this. I have 3 of these power invereters I keep buying and blowing up they all have the same symptoms with no burnt internal components and just the red fault light on. I would really like to know how to service these things because I need them for work and they are expensive. I am shocked to see how similar they are to car amplifiers. I have all of the outputs and power supply FETs left over from other amp repairs I have done. so most of the parts I have already laying around.

1.) CDE4013BE SMPS Controller
2.) KA3525A
3.) LM339N Comparator
4.) LM358N
5.) NE556N Timer

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

The KA3525A is the SMPS controller.

You say the IRF640 is turned on? It's D-S voltage is 200v - I am guessing that it is in the DC-AC inverter section. Is there any ~170v rail anywhere? If you cant find it, try looking for high voltage capacitors (I.E. 200v, electrolytic). If the DC-DC converter is working, then the problem is in the DC-AC converter section.

-Ben

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

the IRF640 seems to be switching ground i have 15v on the gate and drain and source go right to ground.

i dont have anything measurable larger anywhere on the board larger then 15v. not at the caps not at the linear tranformers.

the caps all test fine with my ESR meter.

would you mind explaining to me what is the purpose of the IRF3205, IRF640, FES8JT and the linear transformers? in car amps i have only IRF3205 to generate rail voltage then i have pos and neg outputs this configuration is slightly different i only have N channel IRF640s and a bunch of diodes i dont understand what for.

thanks for the quick response

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

the IRF640 seems to be switching ground i have 15v on the gate and drain and source go right to ground.

i dont have anything measurable larger anywhere on the board larger then 15v. not at the caps not at the linear tranformers.

the caps all test fine with my ESR meter.

would you mind explaining to me what is the purpose of the IRF3205, IRF640, FES8JT and the linear transformers? in car amps i have only IRF3205 to generate rail voltage then i have pos and neg outputs this configuration is slightly different i only have N channel IRF640s and a bunch of diodes i dont understand what for.

thanks for the quick response

Could we have some larger shots of the WHOLE board?
And some shots of the back of the PCB. Thanks!

Car amps have transformers in them too, they are used to boost the voltage. Those usually are round doughnut types. These are just the regular 'E' types. Both operate on a high frequency, so they are ferrite cores (iron cores don't work well at high frequencies).

Are any of the FES8JT's shorted or open-circuit? They are high voltage diodes, and they'll rectify the high voltage output from the transformer(s).

-Ben

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

in my original post i put a link in there for another thread with some other guy with the same hardware as mine with some pictures and other people trying to help out. For some reason the link didnt work so i will try again, he has some good pictures.

http://www.diyaudio.com/forums/power...-inverter.html

The diodes; with all of them on the board and not removed i put my meter on ohms and get very high resistence in both directions. around 480k ohms one way and 30M ohms the other way. with the meter on diode check i get .4v one way and infinte on the other way. i cant find anything that i would consider a short

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

in my original post i put a link in there for another thread with some other guy with the same hardware as mine with some pictures and other people trying to help out. For some reason the link didnt work so i will try again, he has some good pictures.

http://www.diyaudio.com/forums/power...-inverter.html

The diodes; with all of them on the board and not removed i put my meter on ohms and get very high resistence in both directions. around 480k ohms one way and 30M ohms the other way. with the meter on diode check i get .4v one way and infinte on the other way. i cant find anything that i would consider a short

Did you check all the little 25A blade-style fuses?

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

Yes I did and they don't have voltage at the the terminals and they all have less than 1 ohm across them.

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Yes I did and they don't have voltage at the the terminals and they all have less than 1 ohm across them.

No voltage there??? Are you sure your measuring the voltage correctly?
Or do you mean there is no voltage across the fuses? There shouldn't be any if they are good.

When measuring the voltages in this thing, keep the negative probe lead on the negative connection (I.E. the big fat black cables). What is the voltage(s) after the fuses?

Are those transistors by the KA3525A any good?

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

I have 0v DC on either side of the blade fuses and I have checked all of the transistors for shorts in the board so far I haven't pulled anything.

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

I have 0v DC on either side of the blade fuses and I have checked all of the transistors for shorts in the board so far I haven't pulled anything.

What is the voltage(s) before the fuses, I.E. right where the red wire is soldered to the PCB? It SHOULD be ~12v --- if it is, then either the fuses are burnt out, or there is a bad connection on the black (negative) wire. If there isn't voltage there either, then I still would suspect some issue with the power input wires.

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

sorry i posted that from my phone because i was away from my computer, i was working off of my memory and i was wrong, there is battery voltage on both sides of the fuse.

i have 14v DC going into the transformers and 170mv AC coming out

[redwire]

Re: Power Inverter for a Car (Diagnose + Repair)

I couldn't find a schematic, but you can see they have split it up into 4 smaller push-pull stages, then they combine the output. Hence 8 fuses/ 4 pairs of mosfets/4 pairs of rectifier diodes/4 transformers, so each stage is 1750/4 or 438W.

The (rectifier) outputs are then paralleled to create the 170VDC bus voltage on the big blue capacitors. This 170VDC is then commutated by the IRF640's (Q3,4,6,9,11,13,17) to make a pseudo-sine wave. This also looks paralleled, in pairs to make up the H-bridge.

Check the Gate-Source resistance on all the mosfets, looking for shorted ones. If none of the eight 25A fuses are blown, then assume the primary side mosfets are ok.
That leaves the IRF640's which frequently fail.

I see a black arc spot on the underbelly of... L2? so that would definitely damage things.

I don't see any bleeder resistors so be careful, those blue caps (470uF 250V) can hold a charge. You should jumper with a power resistor to discharge them.

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Here is a hint:

The PIN-10 of the KA3525A is the shutdown pin. The pin is at 5v according to your measurments. The threshold voltage for the shutdown pin is about 1.3v - above the voltage, the shutdown is activated.

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

i have no shorts in the IRF640s the lowest number i can get is 60k Ohms resistance.

there is no burn mark around L2 it must just be a shadow or bad picture.

should i pull the IRF640s anyways and see if it removes the 5v to pin 10?

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Could we get a picture of the row of transistors near the KA3525? What part numbers are they?

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

sorry for the late response, i am back tho now

all the ones with pink marker (Q26, Q28, Q36, Q34) are 1n2907a

every other one in between (Q25, Q27, Q37, Q35) is a 1n2222a

the oddball off to the side (Q38) is a 1n2222a

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Can you pull out all the IRF640's and test them for shorts?

[scampo77]

Re: Power Inverter for a Car (Diagnose + Repair)

they are alll out and no shorts and now on the empty pads i have.....

Gate 7vdc
Drain 150dc
Source is fluctuating from .8v-1.2v

and i still have ~5vdc on pin 10 of the KA3525

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Very strange problem. Because the voltage on the HV bus has sprung up. The IRF610's are OK. With them in place there is no HV bus voltage. I think either 1. The circuit isn't pulsing the MOSFETs right 2. The MOSFET drivers are dead.

I have no clue if the HV bus is supposed to be 150v. 120VAC is actually 170v p-p.

Will look at this more later....

[ben7]

Re: Power Inverter for a Car (Diagnose + Repair)

Can you check Q7, Q12, Q24 and Q16?