Help with rockford 1501bd

[stoke]

hi, i replaced on this amp 4 irf6215 and 4 irf3415, now the amp power up but makes like a oscillation noise on the circuit board and there some current excess flowing.

 

[stoke]

i leaved the amp on for a few seconds and blew up some output transistors

 

[Perry Babin]

Did you check the gate resistors for the outputs you replaced?

 

[stoke]

yes, all ok

 

[Perry Babin]

Do you have an oscilloscope?

 

[stoke]

no

 

[Perry Babin]

Remove the defective output transistors.

Discharge the rail capacitors by shorting between the twisted red/black wires with a dummy load resistor.

Measure the resistance between leg 1 of the MIC4420 and the other legs of the MIC4420 (nearest the blown outputs). What's the lowest resistance you read between those legs.

 

[stoke]

on U6 with pos on leg 1

2=290
3=1.75k
4=300
5=0

 

[stoke]

on U6 with pos on leg 1

2=290
3=1.75k
4=300
5=open

 

[Perry Babin]

That seems about right. I don't know what else you can do without a scope. It could be that you damaged them when you soldered them to the MEHSA insulator and that what caused their failure. To find virtually any other problem, you'd need a scope to check the drive waveforms.

 

[stoke]

i pull out one side of the red and black wire in both side, and when i powered up the amp i can hear a rear noise on the circuit board and it is drawing current.

 

[stoke]

if i pulled out both twisted red & black cables, what could be the cause of a buzzing sound on the circuit board and an excess of current draw??????

 

[Perry Babin]

Connect only remote and ground (no B+). Measure the DC voltage 'directly' on the leg (at the body of the transistor) of EVERY power supply FET. If they ALL read the same, post the voltage. If one or more are not the same, post the voltage on the one that's different and the the voltage on the others.

 

[stoke]

5 volts on all of then......

 

[stoke]

i get another rockford 15001bid and i replace 4 power supply transistor and when i power up the amp it make the same sound of the other and there is some current drawing the same problem on both amp.

 

[Perry Babin]

How much current is it drawing?

It's VERY rare that any of the power supply FETs survive when any one fails in a power supply. If 4 needed to be replaced, you should have replaced the other 4 also. I'm assuming that the other power supply was not damaged.

 

[mike49504]

Listen to Perry on tis amp he knows theese amps well as he helped me fix a few of them.

The noise your probably hearing is loose windings on the transformer Every 1500 bd Ive fixed had loose windings on the transformer so not that much of a deal try twisting/pulling on the transformers to see if the noise goes away or gets worse.

Also like perry said if you only replaced 4 fets that may be part of the problem.

All the Bd's ive dealt with a few fets were shorted and the other ones were leaking between the legs In the same bank of fets. There are 2 banks of fets in this amp 1 for the first supply and 1 for the second.

When i replace the power supply fets I also replace all the drivers for the fets as well the MPSA56 and MPSA06's i also check the gate resistors make sure they are within tolorance.

Hope this helps.

 

[stoke]

i found some paint burned and uncover cables on one transformer

 

[Perry Babin]

It's likely it's unrepairable. You'll have to find a replacement if it's shorted. Is this the one closest to the power/ground terminals?

 

[stoke]

yes, its the one closest to power/ground terminals? what could be the best way to check this transformer