fosgate series 1 2600x

bdgf2004 · 16th January 2011, 01:23 AM

in one channel the bottom half of the output cuts in and out quickly and randomly. this is with no load. i set my meter to diode check and compaired readings in both channels on several components and so far they all seem identical. i think i had this problem before in another fosgate amp and perry said it was probably something in the protection circuit.

Perry Babin · 16th January 2011, 02:44 AM

In this amp, I'd suspect broken legs on the outputs.

bdgf2004 · 16th January 2011, 03:40 AM

i've pressed and wiggled on the outputs with no result, should i remove them?
i noticed that on the wire terminals the B+ is located next to the output of the defective channel. i mentioned this because the plastic divider between the terminals is broken making it very easy for the B+ to come into contact with the speaker output.

Perry Babin · 16th January 2011, 02:33 PM

Generally, if the legs are broken, moving the body of the transistor would make it distort. Are you losing negative rail voltage? Check at the leg of the output transistor.

bdgf2004 · 16th January 2011, 03:21 PM

i have full rail voltage on both the outputs in the defective channel. but i did notice that on pin #1 of Q427 i am getting negitive rail voltage, it will kind of flash up and down between a few volts but stays well in the negitive. i compaired the the readings of the outputs while still in the circuit and all are identical with my meter on diode check (now i have a fluke 112). should i pull Q427 to see if it is defective?

Perry Babin · 16th January 2011, 04:35 PM

The voltage on that pin should remain about 3.5v above the negative rail. If it's jumping significantly higher and the amp isn't drawing excessive current or producing significant DC voltage on the speaker terminal, I'd suspect that the transistor is defective.

bdgf2004 · 16th January 2011, 09:19 PM

i checked the fet (Q427) out of the circuit and it tested okay. so to be sure i installed a new IRF540 and i does the same thing. since i had the fet out i check the pad for pin #1 and looks a little different but it is still jumpy.

Perry Babin · 16th January 2011, 10:03 PM

The voltage on the gate pad won't be reliable for troubleshooting with the output out of the circuit. You should reinstall the output.

Does Q410 appear to have overheated?

Do you have any freeze mist or canned air?

bdgf2004 · 17th January 2011, 01:22 AM

i removed and checked Q410 and it seemed okay. so i went ahead and tried a new MMBTA56 and now the amp seems to work fine. so far it's been playing for about 15 minutes.

16th January 2011, 02:44 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	In this amp, I'd suspect broken legs on the outputs. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

16th January 2011, 02:33 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Generally, if the legs are broken, moving the body of the transistor would make it distort. Are you losing negative rail voltage? Check at the leg of the output transistor. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

16th January 2011, 04:35 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The voltage on that pin should remain about 3.5v above the negative rail. If it's jumping significantly higher and the amp isn't drawing excessive current or producing significant DC voltage on the speaker terminal, I'd suspect that the transistor is defective. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

16th January 2011, 10:03 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The voltage on the gate pad won't be reliable for troubleshooting with the output out of the circuit. You should reinstall the output. Does Q410 appear to have overheated? Do you have any freeze mist or canned air? __________________ 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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16th January 2011, 01:23 AM	#1
bdgf2004 diyAudio Member Join Date: Oct 2010	fosgate series 1 2600x in one channel the bottom half of the output cuts in and out quickly and randomly. this is with no load. i set my meter to diode check and compaired readings in both channels on several components and so far they all seem identical. i think i had this problem before in another fosgate amp and perry said it was probably something in the protection circuit.

16th January 2011, 03:40 AM	#3
bdgf2004 diyAudio Member Join Date: Oct 2010	i've pressed and wiggled on the outputs with no result, should i remove them? i noticed that on the wire terminals the B+ is located next to the output of the defective channel. i mentioned this because the plastic divider between the terminals is broken making it very easy for the B+ to come into contact with the speaker output.

16th January 2011, 09:19 PM	#7
bdgf2004 diyAudio Member Join Date: Oct 2010	i checked the fet (Q427) out of the circuit and it tested okay. so to be sure i installed a new IRF540 and i does the same thing. since i had the fet out i check the pad for pin #1 and looks a little different but it is still jumpy.

17th January 2011, 01:22 AM	#9
bdgf2004 diyAudio Member Join Date: Oct 2010	i removed and checked Q410 and it seemed okay. so i went ahead and tried a new MMBTA56 and now the amp seems to work fine. so far it's been playing for about 15 minutes.

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