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Rockford Fosgate 4600X series one power supply
Rockford Fosgate 4600X series one power supply
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Old 7th February 2020, 04:57 AM   #1
audioartspeaker is offline audioartspeaker  Canada
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Default Rockford Fosgate 4600X series one power supply

Iíve got a Rockford 4600 that blew an output FET. I pulled the two FETs on that channel, and poking around I discovered that the main rail + caps are at +18V which is probably about right as the caps are 25v rated. But the - rail is at -27V. Any ideas where to look? Canít find any bad components. I even replaced the TL494 and LM339M chips, no change. No 'scope to check waveforms yet, but I have one coming...
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Old 7th February 2020, 03:15 PM   #2
Perry Babin is offline Perry Babin  United States
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Was the black probe on the amp's main ground terminal?
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Old 7th February 2020, 03:58 PM   #3
audioartspeaker is offline audioartspeaker  Canada
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I was just measuring across the caps. I just re checked, and referenced to ground they are actually +27.5V on one rail and -18V on the other.
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Old 7th February 2020, 04:18 PM   #4
Perry Babin is offline Perry Babin  United States
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What is the voltage on the center legs of the rectifiers D1 and D2?
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Old 7th February 2020, 05:41 PM   #5
audioartspeaker is offline audioartspeaker  Canada
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Same, D1 +27.5V, D2 -18V

I have the schematic if that helps.
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Old 7th February 2020, 06:44 PM   #6
Perry Babin is offline Perry Babin  United States
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Although it's unlikely, it's possible that the positive rail cap is defective and allowing a lot of ripple to be on the rail and the meter is reading that.

Do you have another capacitor that you could parallel across that capacitor. It doesn't have to be identical. Anything 100uF or greater will likely be OK.
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Old 8th February 2020, 12:43 AM   #7
audioartspeaker is offline audioartspeaker  Canada
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I took out the rail caps and tested them.they are marked 2200uf and measure 1700uf. I temporarily replaced them with some 500-1000uf caps. The voltage is fluctuating a bit more but is essentially the same.
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Old 8th February 2020, 12:52 AM   #8
Perry Babin is offline Perry Babin  United States
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Why did you pull the outputs?

Do you have a solder bridge between any of the terminals of any of the output transistors?
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Old 8th February 2020, 03:10 AM   #9
audioartspeaker is offline audioartspeaker  Canada
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One FET was blown, so I pulled that pair and the driver to test. Now I can't remember why I pilled the remaining two pairs. One pair is still in.
(this is a four channel amp, there is one pair per channel) I have replacements for the one channel, do you think I should re install them all?

I checked all of the empty pads with a multimeter, no shorts.

I have been powering it up with a current limited power supply set to 10V, and the amp is drawing 0.5A, nothing getting hot. I tried stepping it up to 12V, and the rails went up to +34V (definitely too high, as the rail caps are 25V) and -22V, current stayed at 0.5A. The power LED is coming on through all of this when I apply voltage to the remote terminal.
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Old 8th February 2020, 03:55 AM   #10
Perry Babin is offline Perry Babin  United States
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What is the DC voltage on the capacitor for the driver voltage (V++)?
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