Rockford Fosgate T5002

[mike49504]

I got another one of theese in for repair..

The problem with the amp is it will keep cutting out and going into protection mode ...

If you have the crossover on full range or high pass and listen to midrange speakers the amp is fine..

If you connect a subwoofer to the amp and set the crossover to low pass the amp will go in and out of protection mode..


Hooked this amp up in several different cars and several different subs also amp will go in and out of protection mode when the low pass crossover is on and a sub is connected...


Any ideas??

 

[seankane]

Sometimes these switches can short. With the switch in low pass is there any DC on the metal case of the switch itself?

Have you tried connecting a sub woofer to the amp in high pass and full range just to see what it does?

 

[Perry Babin]

What was the original problem?

What did you do to the amp to this point?

 

[mike49504]

This amp ive done nothing at all to it... Just got it in for repair..


The guy told me that it has always had the same problem with going in and out of protection mode when a sub is connected and he thought that maybe it was something in his car so he hooked the amp up in 3 different cars and hooked differnt subs up to it and has had the same problem with the amp ..


So he brought it to me to see if i could figure it out...

I can get the amp to do the same thing on the bench..

 

[Perry Babin]

It has two channels. If you have the speaker connected to only one channel at a time. does either or both cause the amp to go into protect?

 

[mike49504]

Both channels cause it to go in and out of protection

 

[EBBCO]

These amps have an issue with the switches in them, also check the RCA shell's on amp. Go from shell to the I.c chip, follow each trace, there not common. One comes undone it will cause lp mode to phase out 180 and protect.

 

[Perry Babin]

Post the DC voltage on all pins of U3 before it goes into protect. Add the voltages for the pins that change after it goes into protect.

U3
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:

 

[mike49504]

U3
Pin 1: 9.38
Pin 2: 14.31
Pin 3: 14.76
Pin 4: 0.22
Pin 5: 1.18
Pin 6: 0.01
Pin 7: 4.98
Pin 8: 0.58
Pin 9: 9.77
Pin 10: 0.11
Pin 11: 1.00
Pin 12: 0
Pin 13: 0.46
Pin 14: 4.97


Voltages when it protects

U3
Pin 1: 0.04
Pin 2: 13.94
Pin 3: 14.36
Pin 4: 0.54
Pin 5: 1.16
Pin 6: 7.00
Pin 7: 4.98
Pin 8: 0.59
Pin 9: 5.98
Pin 10: 0.30
Pin 11: 0.99
Pin 12: 0
Pin 13: 0.46
Pin 14: 4.97

 

[Perry Babin]

Remove R58 from the circuit. This will disable the shutdown circuit so you must be careful (15 amp fuse, transistors tightly clamped to the heatsink). I'm assuming that the amp will go into protect mode relatively easily and would not blow the 15 amp fuse.

Does the amp work as it should with the protection circuit disabled?

 

[mike49504]

With R58 removed the amp will not power up at all

 

[Perry Babin]

Find the end of R55 that's connected to 5v. Solder a resistor (any value will work) from the 5v pad to the end of R57 that is NOT connected to ground. That should allow the amp to power up.

 

[mike49504]

So i leave R55 and 57 in circuit when soldering in a resistor between the 2 ?

 

[mike49504]

Ok with R58 removed and a 100 ohms resistor solderd from the 5 volt end of
R55 to the end of R57 thas not connected to ground..


The amp still does the same thing

 

[Perry Babin]

The protect LED should still light up but the audio should not. Does the power supply shut down or the audio cut out when the protection LED lights up?

 

[mike49504]

Audio side cuts out..


With B+ ground and remote applied only i get 0.68 volts on the gate legs for the power supply fets is this normal?

 

[Perry Babin]

Reduce the 12v power supply input voltage. Does the voltage on the gate increase (can also be seen as an increasing pulse width on the scope)?

Is the rail voltage dropping when the amp cuts out?

Does it appear that anyone has worked on the amp before?

 

[mike49504]

If i reduce the input voltage The voltage on the gates increase's to 5.30 volts.. And can be seen as an increasing pulse..


The rail voltage only drops about 1 volt when the amp cuts out..


It appears that the amp has had new outputs installed and 1 A06 and 1 A56 transistor replaced.. Bias pots are fully counter clockwise

 

[Perry Babin]

Are the 0.1 ohm source resistors within tolerance?

Have any been replaced?

 

[mike49504]

Heres the problem I found the amp has 1 ohm resistors in it right now.. The other T5002 i have here has 0.1 ohm resistors in it.. Could this cause the problem im running into ?