American Bass CX 1200 D

[mike49504]

Got another one of theese in for repair.

If i remove the IRF9640's and leave the 640's in The amp powers up.

If i have both the 640's and 9640's in the amp it stays in protection mode.

I tested all the Outputs and they all seem to test fine. ANY ideas?

[mike49504]

Ok i tracked it down to the driver board.

Heres a list of Stuff im gonna need to rebuild it. Just wondering if you can confirm theese are correct before i place an order.

Surface nount diodes and transistors.

2F=BC850B Location:Q10

A6=BAS16 Location12,D6,D5,D11

8F=MMBZ5231B Location8

Z7=BZX84-C8V2 Location7,D9

1P= MMBT2222A Location:Q9

[mike49504]

Ok disreguard my last post for now.

I pulled a KSP2907A From the board this is what i get.


1-2:OL
1-3:OL
2-3:30.79 Mohm

probes reversed

1-2:34.25
1-3:OL
2-3:OL

PN2222A

1-2:34.98 and meter climbs
1-3:OL
2-3:OL

Probes Reversed
1-2:OL
1-3:OL
2-3:30.64

Do either of theese appear to be defective?

[Perry Babin]

Those look OK. I'm assuming that 30.64 is Mohms, not ohms.

It's good to use both diode check and resistance when checking transistors. For example, the one that had the climbing readings would have given you a stable, more reliable reading on diode check.

[mike49504]

I listed some parts in post 2 wondering if you could confirm thoose are correct. If i pull all of the outputs amp will power up . If the outputs are in the amp the amp stays in protection but they all test fine.

[Perry Babin]

I have no experience with this particular amp so I can't give definitive answers.

Are all of these parts definitely defective?

Did you look up the datasheets for each one and confirm that the markings were listed in the datasheet AND that the parts were identical (may need a dial caliper to measure accurately)?

Even then, there's no guarantee. You'd need to find other parts in the amp with similar markings and confirm that the polarity of the transistor (NPN/PNP) is the same as those in the datasheets.

[mike49504]

Any ideas on what to check? I checked this and all seem to test good .

Only thing that worries me is the class D chip is bad.

[Perry Babin]

On those, I've only seen the Zeners fail and one time one of the (missing) transistors failed.

[mike49504]

The zeners check fine (silver diodes on same side as the class D chip)


Heres what i have in diode check on the Transistors

2907

1-2:OL
1-3:Ol
2-3:0.613

Probes reversed

1-2:0.626
1-3:OL
2-3:OL

2222A

1-2:0.627
1-3:OL
2-3:OL

probes Reversed

1-2:OL
1-3:Ol
2-3:0.616

They seem to test fine to me.

Do i need to remove the smd Diodes and Transistors to test them?

[Perry Babin]

Yes. Those seem OK.

I don't know how the transistors are being used so I don't know what's connected to them. You can really only check the see if they're shorted in the circuit. If you want to check them more thoroughly, lift two legs of each one and check them.