Rockford fosgate Bd1500.1

[mike49504]

I recieved yet another one of theese amps in for reapir.

The power supply fets were shorted so i replaced them with IRF3205's .
Also replaced the 10 ohm gate resistors. The drivers are also new.

I unsoldered the red/black twisted wires from the board on 1 side .

When trying to power it up as soon as i add remote voltage it draws excessive current.

Any ideas what this might be?

 

[FireII]

Shorted outputs?

 

[mike49504]

The problem is in the power supply Once you unsolder the red and black wires it disengauges the output section.

 

[FireII]

I see I don't know much about rockford repairs.

Did the rectifiers survive? Possible shorted cap? Just throwin things out there as I have another budweiser =)

 

[Perry Babin]

Power it up without B+ connected (only remote and ground). Does the gate drive waveform look OK?

 

[mike49504]

Perry,

is it 10 us 5 volts div?

 

[mike49504]

Im gonna have to go buy a new probe first since the one i have is not reading .

So i will go get a probe and check to see if i have good square waves on the gates and let you know

 

[Perry Babin]

10uS and 5v would be a good starting point.

 

[mike49504]

there is 16 Power supply fets in this amp.

On 4 of them in the first bank of fets i get a nice square wave. The last 2 in that set i get a wavy line.

Next bank of fets i dont get a nice square wave on that bank.

Where would i go from here?

 

[Perry Babin]

If the waveform isn't going to ground, the PNP drivers are defective. Check the gate drive signal on the outputs of the 3526, on the bases of all drivers and on the emitters of all drivers to see which don't have a square wave signal.

 

[mike49504]

On the 3525

Pin4 OSC Output: nothing

PIN11 Output A Nice square wave

Pin14 Output B Nice square wave

Q17,19,20,21 square wave is good on the emmitters and bases

Q27,28,29,30 Have nice square waves on both emitters and bases.

 

[Perry Babin]

The next point is on the gate resistors. Check the drive signal on both ends of each resistor.

 

[mike49504]

I looked up the wrong data sheet for starters.

The 3526 is the one i needed and i have good square waves on pins 13,16

The following gate resistors have 1 side with bad waves

R62
R69
R71
R76
R83
R86
R92

The all have bad waves on 1 side of the nothing near a square wave.

 

[Perry Babin]

Measure their resistance. Do they all read 10 ohms?

 

[mike49504]

When i put new fets in i replaceds the 10 ohm resistors now they read out of tolerance.

Guess i will replace the gate resistors again and let you know what i come up with.

 

[mike49504]

Something still isnt right The first pic is the first banks of fets PIC 2 is the second banks of fets

 

[Perry Babin]

The scope appears to be set to 2v/div. Set it to DC coupling. Move the trace to the middle reference line and post the signals on those points again.

 

[mike49504]

I replaced the drivers again.

As soon as i apply ground and remote only drivers Q17,19,20,21 go up in smoke

Any ideas on what might cause this?

 

[Perry Babin]

Are you 100% sure that you have the NPN/PNP transistors in the correct locations? The collector of the PNP transistors will be directly connected to ground.

Are you sure that the FETs aren't defective?

 

[mike49504]

The collector of the mpsa56 is directly connected to ground so i have thoose right .

I willull the fets again and test them to see if 1 is shorted