rockford fosgate power 650 mosfet

[mike49504]

ok i replaced a fuse in that channel didnt notice it was blown on irf540 -3.08
irf9540 = 2.26

The bias pots for all 4 channels are fully counter cloclwise already didnt turn them at all . someone worked on this before i recieved it

 

[Perry Babin]

Those voltages don't look like they could be causing any problems.

Do all 540s read the same and all 9540s read the same in that channel?

Has the same output in one particular location failed repeatedly?

 

[mike49504]

all 540's and 9540's test the same in that channel. its when you hooked up the speaker wires that channel blows the outputs but i was using some new 540's and some old 9540's and some drivers were new some were old. Now everyting is brand new

 

[Perry Babin]

Does it still draw excessive current with no speakers connected?

If you don't know, measure the DC voltage across the 1.8 ohm resistor.

 

[mike49504]

ok the wierd thing is i put it back in the sink. Powerd it up and a big spark came for either the transformer or cap didnt see which one but the amp is up and playing on my bench right now. Working perfectly and not drawing much current like 4 amps while playing music at low vol

 

[mike49504]

ok figured out what it was i have to do 1 more thing to this amp and it should be good to go off to the next 1 i have to fix.

 

[Perry Babin]

Try moving the transformer to see if it does it again.

To set the bias, clamp everything down, insert the resistor in the B+ line and connect your multimeter across the resistor. Power up the amp and SLOWLY turn the bias clockwise until you just see the voltage across the resistor increase VERY slightly. You want the slightest increase possible.

Run the amp up to or very near thermal shutdown. You'll have to run the amp on direct B+ (no resistor in line) but every 5 minutes (give or take), insert the resistor in line and recheck the voltage across the resistor at idle. It should remain relatively close to the original voltage (after biasing all 4 channels).

If your amp meter on your supply has enough resolution at low current, you can monitor the current draw there.

 

[mike49504]

ok i do not get this amp. I replaced all of the outputs all of the drivers. some resistors and some caps and op amps I turned down the bias pots like u said and the amp worked fine

I put the amp together 100% so i could hook it up and set the bias.

Now the left channel is sending 29.68 volts on the output i checked the outputs they seem to test fine i checked the drivers they also seem to check fine. Wondering what i check from here

 

[Perry Babin]

Fuse blown?

Speaker wire color for that channel?

Voltage on op-amp for that channel?

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:

 

[mike49504]

left channel thge wire is white
pin1=0.34
2= 0.5
3= 0.34
4= -17.41
5= 0.14
6=0.54
7=18.40
pin8= 18.49

 

[Perry Babin]

It appears that the op-amp has failed. With the inverting input (pin 6) above the non-inverting input (pin 5), the output (pin 7) should be near the negative rail, not the positive rail.

 

[mike49504]

replaced the op amp heres what i get for voltages

1=0
2=0
3=0
4= -17.70
5= -3.99
6= 0.2
7=0
8=18.41

wondering if this is correct values or has this opamp failed also

 

[Perry Babin]

It appear that you've lost the connection to ground on pin 5.

Did you omit the voltage on the first 3 pins or does it actually read 0v on those pins?

 

[mike49504]

it really says 0 volts

 

[Perry Babin]

Did you repair the ground on pin 5?

We'll deal with the other channel after you get this one repaired.

 

[mike49504]

Back to this amp. The problem im having with this amp now is.

2 channels are dead no sound

1 channel is distorted like crazy

1 channel plays perfect

Ive replaced all of the outputs,all of the drivers for the outputs,all opamps(tlo72cn and lm833's a few reisitors a few 10uf capsand i set all the bias pots fully counter clockwise

Im at a loss Wondering where i go from here?

 

[Perry Babin]

Do you have signal reaching the op-amps for the dead channels (we can work with the distorted channel later)?

 

[mike49504]

Ok Perry,

On the left channel that is distorted There are what i think are transistors they are marked

d41d8 h9104 and d40d8 j 8927

I seen both theese go up in smoke while trying to test

wondering what the part numbers are and where i might be able to get them since i know theese are bad

 

[Perry Babin]

D40D8 and D41D8 are the part numbers but they have long been discontinued. Octopart is showing a few distributors with stock.

Pull the fuses out of the good channel and this channel and lets concentrate on the two dead channels.

 

[mike49504]

Wondering if there is a good cross to theese parts since the places that do have them probably want an arm and leg for them you gotta send a targeet price for them and all that good stuff