Rockford Fosgate 100x2

fongman · 5th November 2009, 02:13 AM

Hi, i have this old 1996 fosgate 100x2 amp This amp was working good when I stored it away and now only one channel works. I tested the speaker output and got 32.4v on the right channel? I check alll the output transistor and the 1 ohm resistor on both side. They check out okay. The left channel is fine and plays music fine. Nothing was burn. What am i missing here. I would like to say thanks to those of you that help me before. Thanks to Perry for all the help and time. I know he's busy i appreciate Perry your time.

Perry Babin · 5th November 2009, 04:42 AM

If you're absolutely sure that none of the output transistors is shorted, give me the DC voltage on each FET in the defective channel with the amp powered up (no audio). Place the black probe in leg 3 of the FET being tested and the red probe on leg 1 and then leg 2. For each transistor, post the circuit board designation.

Q#
Leg 1:
Leg 2:

Q#
Leg 1:
Leg 2:

Q#
Leg 1:
Leg 2:

Q#
Leg 1:
Leg 2:

fongman · 05:05 AM

Q#225
Leg 1: 65.3v
Leg 2: .261v

Q#215
Leg 1: 65.3v
Leg 2: .261v

Q#219
Leg 1: 0v
Leg 2: -17.66v

Q#224
Leg 1: 0v
Leg 2: -17.66v

Perry Babin · 5th November 2009, 04:56 AM

Did you have the black probe on the 3rd leg of each transistor being tested?

What are the circuit board designations for each of the transistors?

fongman · 5th November 2009, 05:10 AM

Yes i just add the negative on the 17.66v. I start on the bottom left of the amp in the picture that i posted. The reading should be down to up.

Perry Babin · 5th November 2009, 05:25 AM

If you have 65v from gate to source on the top 2 FETs, they're VERY likely defective but I see no way to get that voltage. Confirm that you had the probes as shown in the attached drawing.

fongman · 5th November 2009, 05:37 AM

Just like that. I might have some extra that i can change?

fongman · 5th November 2009, 06:05 AM

I try two of the irf540 and still the same?

Perry Babin · 5th November 2009, 06:12 AM

Are you sure it's 65.3v and not 65.3mv? The drive circuit can't produce that much drive voltage.

fongman · 5th November 2009, 06:18 AM

its 65.3vdc on my meter.

5th November 2009, 02:13 AM	#1
fongman diyAudio Member Join Date: Jan 2009	Rockford Fosgate 100x2 Hi, i have this old 1996 fosgate 100x2 amp This amp was working good when I stored it away and now only one channel works. I tested the speaker output and got 32.4v on the right channel? I check alll the output transistor and the 1 ohm resistor on both side. They check out okay. The left channel is fine and plays music fine. Nothing was burn. What am i missing here. I would like to say thanks to those of you that help me before. Thanks to Perry for all the help and time. I know he's busy i appreciate Perry your time.

5th November 2009, 04:53 AM	#3
fongman diyAudio Member Join Date: Jan 2009	Q#225 Leg 1: 65.3v Leg 2: .261v Q#215 Leg 1: 65.3v Leg 2: .261v Q#219 Leg 1: 0v Leg 2: -17.66v Q#224 Leg 1: 0v Leg 2: -17.66v Last edited by fongman; 5th November 2009 at 05:05 AM.

5th November 2009, 04:56 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you have the black probe on the 3rd leg of each transistor being tested? What are the circuit board designations for each of the transistors? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

5th November 2009, 06:12 AM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Are you sure it's 65.3v and not 65.3mv? The drive circuit can't produce that much drive voltage. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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5th November 2009, 04:42 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If you're absolutely sure that none of the output transistors is shorted, give me the DC voltage on each FET in the defective channel with the amp powered up (no audio). Place the black probe in leg 3 of the FET being tested and the red probe on leg 1 and then leg 2. For each transistor, post the circuit board designation. Q# Leg 1: Leg 2: Q# Leg 1: Leg 2: Q# Leg 1: Leg 2: Q# Leg 1: Leg 2: __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

5th November 2009, 05:10 AM	#5
fongman diyAudio Member Join Date: Jan 2009	Yes i just add the negative on the 17.66v. I start on the bottom left of the amp in the picture that i posted. The reading should be down to up.

5th November 2009, 05:37 AM	#7
fongman diyAudio Member Join Date: Jan 2009	Just like that. I might have some extra that i can change?

5th November 2009, 06:05 AM	#8
fongman diyAudio Member Join Date: Jan 2009	I try two of the irf540 and still the same?

5th November 2009, 06:18 AM	#10
fongman diyAudio Member Join Date: Jan 2009	its 65.3vdc on my meter.

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