Hifonics bxi 12000d

[Achim1409]

I got this hifonics with some output fets blown. Repaired doughter board. Drive board seems OK, and is buffered. On one side I don't get a signal, even no voltage.

One side is negative, the other side has only positive rail voltage. Black probe at sec center. Rail voltage are ok.. Maybe someone has an advice

 

[Achim1409]

So, I changed both drivers, because one was damaged. Left side of the board is high side, right side low side. Signal on low side is OK. But I don't have positive rail on the drive board. Also the driver buffer transistors shows 0v..this design is new to me.. Any suggestions?

 

[Perry Babin]

This driver board is new to me but should be similar to the older boards. Those had no positive rail on the driver board.

What are the part numbers for the drivers on the ends of the board?

Are you saying that the low-side drive from the left driver IC goes to the right (bottom in photo) end of the board?

 

[Achim1409]

See the pictures. The complete row is low side. The other side of the board should be high side.

Buffer transistors are
B649A
D669a
4 pairs of that transistors.
drive ic are irs21844s


Additional this Boards along the mosfets.

 

[Achim1409]

It seems, that the switching frequency is very low.. Maybe still some issues with the drive board.

 

[Achim1409]

If i inject audio signal, the frequency will even drop more down. If I inject 50hz,the signal also goes down to 50hz.. Very strange. I will check the drive board again.

 

[Perry Babin]

These aren't typically clocked so the only reliable drive is the signal you drive into it.

Are the high-side driver transistor collectors connected directly to the high-side supply terminals of the 21844 or do they have a dedicated supply?

 

[Achim1409]

Base is connected to HO
D669A Collector at VB
B6649 Collector at VS

 

[Achim1409]

Emitter of both going to the daughter board ( Fets)

 

[Achim1409]

Found one problem.. One resitor for the protection circuit was short. As soon, as a mosfet was inside, it goes into protect. Now seems better.. Going to test now.

 

[Achim1409]

So,, the low side signal from the previous damaged channel disapear ... But no Protection circuit released... Fets stay cold... Strange, i changed allready the IRS..

 

[Achim1409]

some cold solder joints...found them with heating up the joints.

 

[Perry Babin]

Did that solve all of the problems?

 

[Achim1409]

It seems so. I tested with a 2,4 ohm resistor on the audio out, with a 150 amps PS. If my input voltage drops to about 10v, the upper half of the sine drops.. But I think that's normal.

 

[Achim1409]

I think there is a voltage regulator, which drops below 10v and then the high side mosfets are not fully open anymore.. Or du you have another suggestion?

 

[Perry Babin]

I would not expect it to lose only 1/2 of the drive.

The high and low sides are supplied by the 12v regulator referenced to the lower rail. The low side always has 12v. The high-side only has it when the FETs are switching.

 

[Achim1409]

The good sine is at 10v input, the second at 9.9v input. I will check the drive.

 

[Achim1409]

The drive is dropping in very short cycles... I don't know if I can do something against that.. 9.9v is allready very low input voltage. And I don't know what can cause that, if the 12v regulator is bound to the rail voltage.
..

 

[Perry Babin]

Measuring the voltage across the collectors of the drivers, is the high-side B+ dropping just before the high-side drops out at 10v? Don't try to measure this if there is a chance of slipping and shorting between any terminals.

The problem may not necessarily be at the output board but possibly at the power supply end in a low-voltage protection circuit. I don't think any 12v amp is expected to work at 10v in. That said, it's difficult to drag a healthy 12v battery down to 10v. Would the voltage get that low in the vehicle if the system was capable of supplying power to this amp?

 

[Achim1409]

I expect also, that normally the protection should catch up before 10v..i don't think, that the batterys will that much drained, but the customer is informed about that..