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Old 11th November 2004, 07:45 AM   #1
kelving is offline kelving  United States
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Default Rockfords fosgate 1100a2 output

I have a Rockfords fosgate 1100a2 that powers up, but I have no sound coming out fo the right channel and I have alot of distortion that is making my speakers move back and forth out of my left channel. I opened the amp up and there is no visible damage to inside of the amp. I was thinking it could be faulty or damage output transistors. Could anyone give me some advise on what the problem could be.

P.S. the right channel was repaired before by replacing a transistor and it work well for about 6 months before I started having problems. I want to fix this amp because when it worked it put out gobbs of power.
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Old 12th November 2004, 02:54 PM   #2
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Hi, Kelving,

Rockford's factory is in Tempe, Arizona. Is it near your place? You could just travel there.

Are you familiar with electronics or soldering? If not, better you go to service center.

Anyway, the 1100a2 uses rather sophisticated cct, called inverted output or grounded output topology. This rather difficult to track the malfunction compared to ordinary power amp topology.

First thing to check is the RCA's connector's ground. Usually the ground small pin connected to pcb is broken, just resolder it with small copper wire to the pcb. If it is broken, the amp cannot see the ground point from the head unit. That's why your speaker moving forth and back.

Then clean all the swithes (like hp-lp-fr switch). Spray them with contact cleaner, and shake it left and right many times, to clean the surface contact. If there is any xover card, you should clean them also.

If it is OK, check for the voltages. The rail first. I think the rail should be about +/-60V or more for this type. Is the rail voltage exist? Also check the rail for the opamps. It should be about +/-17V. If it does, then check the voltage at speaker output. Does it near 0mV or have big DC offset?

If every voltage is ok and your amp still do not produce sound, then it could be the protection cct is active. It means you have a malfunctioned output stage. Check for any malfunctioning mosfets at output stage. It uses IRF640 and IRF9640, about 5 pairs for each channel, I think.
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