cadence FXA1200D strange problem...

[mixalos spl]

Good evening friends...im working to this amplifier and i have the above problem...when i plug it with 13,8 volts it starts with 2 amps and immidiatelly getting down at 0.7 amps....after 15 seconds the draw is again 2 amps and the amp shut down...i have a similar amp and the 2 amps appears only when it beggins....then is working fine....i am confused with this...any help???

 

[Perry Babin]

If there are no defective output transistors, it likely has defective driver transistors. I can't see the circuit board designations but if it has two MPSA42s designated as Q124 and Q125, they would be suspect.

 

[mixalos spl]

all right Perry i ll check it tomorrow and i will inform you...as soon as i can...

 

[mixalos spl]

so i have the Q10K-Q11K, and Q8K-Q9K and the code is A42....is this the correct?they drive the output stage....FB31N20D the output fets....

 

[mixalos spl]

there is no defective transistor or driver either output.....everything ok....i am very confused....some times when i touch him....appears the problem....????any ideas?

 

[Perry Babin]

Did you check the drivers for leakage as well as open junctions?

Did the solder connections for the drivers show signs of heat stress?

 

[mixalos spl]

no heat or bad sholders....and the driver transistor are not shorted or open or leakage....i ve check them twice....i suspect the pcb for damage....because even i touch it in any place appears the problem.... i dont know....

 

[Perry Babin]

Intermittently shorted output filter inductors?

Broken legs on the output transistors (possibly inside the body of the transistor)?

 

[mixalos spl]

these amps its a big mess....and the second one appears problem too....no output....and guess what...!!!!no defective output transistors....the worse quality ever...