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Old 31st March 2007, 08:48 PM   #1
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Default help with fosgate 1100a2 amp

I have a fosgate power 1100a2 amp that has dc voltage in one channel .
The left channel works fine, the right channel has 52 volts dc output.
one of the subs seized a coil and took the amp with it.
Would replacing the outputs fix it or is more wrong than I know about?

Ben
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Old 31st March 2007, 09:33 PM   #2
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It's rare to have only the outputs fail. Generally it does more damage.


Does it have any shorted output transistors (it probably does but this needs to be confirmed)?

Have any of the emitter resistors opened (significantly higher than 0.1 ohms)?

Can you post at least one reasonably good photo of the channel that's failed?
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Old 31st March 2007, 10:52 PM   #3
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It has 2 shorted irf 640 and 3 irf9640
Emitter resistors check out ok.


here are some pics
Attached Images
File Type: jpg 1100a2.jpg (82.7 KB, 421 views)
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Old 31st March 2007, 11:10 PM   #4
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Have you pulled them to determine if they were shorted?

In the board, they are in parallel and should look like they're all shorted. If you would have checked from the gate to the other legs, then you could see a difference due to the resistance of the gate resistors.

If you still have a few in good condition, you could clip the defective ones and see if there's any DC offset. If not, there may be no other damage.

As a side note, this amp is probably the same as the 500.2 that I recently repaired. I'm not sure what this topology is but don't look for normal audio on the outputs. The audio is riding on the rails. The transistors drive windings on the power transformer and the speaker output is taken 'from the power transformer'.

These are much less common than the normal amps and don't seem to cause as much damage as the common design.

When you pull the outputs, you'll need to double-check the emitter resistors and the gate resistors.
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Old 1st April 2007, 12:09 AM   #5
impsick is offline impsick  United States
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i cant see where the shorts are.? can you get a closer shot?

i never really liked fosgate amps. more people that i talk to have had failed amps
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Old 1st April 2007, 02:47 AM   #6
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I know people like to bash Rockford amps but they make some of the best amps on the market. Many amplifiers will start to give problems after about a year. You'll regularly see problems like:

Shorted transformers/inductors
Failing solder connections
Leads breaking on components (semiconductors, inductors...)
Blown capacitors (often due to one of the previous problems)
Poor quality/noisy potentiometers and switches

You will rarely see any of those problems in Rockford's amplifiers. They are certainly not common problems.

You also have to understand that many of the most abusive people buy Rockford amplifiers because they have a reputation for producing a lot of power.

If a Rockford amplifier is properly installed, you can expect 10+ years of service from it. The only exceptions have been the HD series amps. They used poor quality SMD electrolytics and they leaked electrolyte.
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Old 1st April 2007, 06:02 AM   #7
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You mean to say Rockford amps can't run at 0.5 ohm mono driving ten 18 inch woofers and deliver 10 tera watts off a single Wal-mart Group 32 car battery

Perry Your absolutely right, especially the call about RF amp owners and what they do to their RF amps in the name of Stupidity.

RF could have added a speaker protection relay and circuit so to prevent voice coil fires when they do fail though, As their older amps at least had internal fuse protection that if untampered with would prevent speakers from becoming flame throwers

But I am all with you Perry on your comments about RF. Just wish they used that speaker relay though, as that channel failing most probably fried his speaker. Seen it a hundred times or more.

Keep up he great work, if he follows your directions his amp will play again
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Old 1st April 2007, 03:25 PM   #8
impsick is offline impsick  United States
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not trying to bash on them. I use to love fosgate back in the late 90's, but seen a few problems since then (probably abusive owners). Most common that i've seen was do to over heating. and a few woofers blown. But to be honest i havent paid much attention to RF since then. I dont dought they may just be the best on the market. i guess im just loyal to my brand
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Old 1st April 2007, 03:37 PM   #9
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outputs are off the board
emitter resistors are ok
I have 2 bad gate resistors the surface mount ones
they are reading 114 and 111 ohms the others read 100 ohms.
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Old 1st April 2007, 05:31 PM   #10
impsick is offline impsick  United States
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i dont think its an accurate if they are still on the board
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