Crossfire amp help please cfa-602

joesch1999 · 17th April 2011, 03:23 PM

I have been working on this amp forever it is very simple class ab I can't believe I am having so much trouble with it. The amp goes on and off with only 11 volts 2 amps applied to it using a linear power supply to power it, that supply does not go over three amps, I have checked everything, with my scope, I have replaced all the pnp transistors out of tolerance, none of the zeneers show any leakage or any signs of getting hot, the amp looks brand new, I know the guy had to of crossed the positive and negative because of the transistors I replaced, I pulled the main zeneer the runs from positive and negative terminals on the amp it's fine shows no backwards continuity meaning using fluke meter with the leads crossed on the zenner, I have replaced a op amp that was out of tolerance but still should have been good, I have pulled every fet n as well as p channel and checked all the transistors running those fets the pnp ones. All the caps are good any ideas because I feel like a idiot lol. I have never had a amp give me this much trouble, that includes jl amps I can fix those np at all lol

Perry Babin · 17th April 2011, 10:53 PM

What do you mean 'it goes on and off'?

joesch1999 · 17th April 2011, 11:13 PM

I mean it pulls excessive current and the power supply shuts down at 3 amps then turns back on keeps doing the same thing

Perry Babin · 17th April 2011, 11:18 PM

Measure the DC voltage across each of the emitter resistors. Does one resistor or a group of resistors read greater than 0.000v DC.

joesch1999 · 18th April 2011, 03:43 AM

I already checked all 0v. I have voltage at the rcas and voltage on the speaker outputs all -10v

joesch1999 · 18th April 2011, 04:14 AM

Here are a couple pics of the amp
DSCN8365resize - My Photo Gallery

DSCN8364resize - My Photo Gallery

Perry Babin · 18th April 2011, 06:33 AM

With the amp disconnected from everything, what's the resistance from the B+ terminal to the RCA shields?

From the non-bridging speaker terminals to the RCAs shields?

joesch1999 · 18th April 2011, 01:48 PM

.2 ohms

Perry Babin · 18th April 2011, 01:53 PM

If you have 0.2 ohms from the B+ terminal to the RCA shields, the transformer is likely shorted. With the meter on those two points, twist the transformer to see if the resistance goes up significantly.

joesch1999 · 18th April 2011, 02:02 PM

from the rca to the b+ is O/L from the non bridging speaker to rca is .2ohms

17th April 2011, 03:23 PM	#1
joesch1999 diyAudio Member Join Date: Jan 2011	Crossfire amp help please cfa-602 I have been working on this amp forever it is very simple class ab I can't believe I am having so much trouble with it. The amp goes on and off with only 11 volts 2 amps applied to it using a linear power supply to power it, that supply does not go over three amps, I have checked everything, with my scope, I have replaced all the pnp transistors out of tolerance, none of the zeneers show any leakage or any signs of getting hot, the amp looks brand new, I know the guy had to of crossed the positive and negative because of the transistors I replaced, I pulled the main zeneer the runs from positive and negative terminals on the amp it's fine shows no backwards continuity meaning using fluke meter with the leads crossed on the zenner, I have replaced a op amp that was out of tolerance but still should have been good, I have pulled every fet n as well as p channel and checked all the transistors running those fets the pnp ones. All the caps are good any ideas because I feel like a idiot lol. I have never had a amp give me this much trouble, that includes jl amps I can fix those np at all lol

17th April 2011, 10:53 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	What do you mean 'it goes on and off'? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

17th April 2011, 11:18 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Measure the DC voltage across each of the emitter resistors. Does one resistor or a group of resistors read greater than 0.000v DC. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

18th April 2011, 06:33 AM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	With the amp disconnected from everything, what's the resistance from the B+ terminal to the RCA shields? From the non-bridging speaker terminals to the RCAs shields? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

18th April 2011, 01:53 PM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If you have 0.2 ohms from the B+ terminal to the RCA shields, the transformer is likely shorted. With the meter on those two points, twist the transformer to see if the resistance goes up significantly. __________________ 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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17th April 2011, 11:13 PM	#3
joesch1999 diyAudio Member Join Date: Jan 2011	I mean it pulls excessive current and the power supply shuts down at 3 amps then turns back on keeps doing the same thing

18th April 2011, 03:43 AM	#5
joesch1999 diyAudio Member Join Date: Jan 2011	I already checked all 0v. I have voltage at the rcas and voltage on the speaker outputs all -10v

18th April 2011, 04:14 AM	#6
joesch1999 diyAudio Member Join Date: Jan 2011	Here are a couple pics of the amp DSCN8365resize - My Photo Gallery DSCN8364resize - My Photo Gallery

18th April 2011, 01:48 PM	#8
joesch1999 diyAudio Member Join Date: Jan 2011	.2 ohms

18th April 2011, 02:02 PM	#10
joesch1999 diyAudio Member Join Date: Jan 2011	from the rca to the b+ is O/L from the non bridging speaker to rca is .2ohms

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