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fosgate 55.2 wont power up
fosgate 55.2 wont power up
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Old 10th February 2018, 06:00 PM   #1
Theophili is offline Theophili  United States
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Default fosgate 55.2 wont power up

hi all recently joined and i am having a problem with an amp i have had for a while.
the device in suspect is a fosgate punch 55.2 circa 1998
pc-1882-a

the amp had been operating great and sudenly lost power, i had been running it in bridged 2ohm which i know its not rated too and more than likely the reason for failure. when voltage is applied to the remote terminal the led is verry dim the left channel is dead and the right is outputing 1.84v dc. i am new to amp repair and am a little stuck any help in what steps to take for testing would be greatly apericiated
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Old 10th February 2018, 07:16 PM   #2
seankane is offline seankane  United States
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Half of the power supply could have failed. With an ohm meter set to ohms and auto range what readings do you get on the power supply FET's from gate to source. Legs 1 and 3?
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Old 10th February 2018, 08:20 PM   #3
Theophili is offline Theophili  United States
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q6 reads ol with meter leads both ways

q7 reads the same
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Old 10th February 2018, 08:48 PM   #4
Theophili is offline Theophili  United States
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both also show 00.5ohm across gate to drain pins 1 and 2
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Old 10th February 2018, 09:11 PM   #5
seankane is offline seankane  United States
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The gate resistors hooked to each gate leg are they burned and or open?
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Old 10th February 2018, 09:16 PM   #6
seankane is offline seankane  United States
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Make sure the channel that is dead is not shorted. If it is you will blow the power supply again. You can clip all the legs of the shorted outputs then safely power the amp.


Likely it needs power supply FET's, gate resistors and power supply drivers. The drivers may have survived, but highly recommended to change.


Once the power supply is up and running, then repair the channel.


Use IRF3205 for power supply with 47 ohm gate resistors. The drivers will be marked 1A and 2A and are near the PWM ic.


Don't have a schematic so not sure board designations on the drivers. Likely Q1 Q2 Q3 Q4
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Old 10th February 2018, 11:50 PM   #7
Theophili is offline Theophili  United States
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the gate resistors for th power supply fets dont apear burnt and they are labeled 101 and measure 101ohms across the resistor and the gate leg. could i sub irfz40's for the mtp50n06v's?
i have located the drivers is there a way to test them?
also what would i check on the channel for a short the output fets?

Last edited by Theophili; 11th February 2018 at 12:11 AM. Reason: new content
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Old 13th February 2018, 12:20 AM   #8
Theophili is offline Theophili  United States
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is there a procedure for testing the driver transistors
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Old 13th February 2018, 04:10 AM   #9
seankane is offline seankane  United States
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Same way you tested the power supply FET's. Test in all configurations with your leads. Most readings should be in "k" ohms or "m" ohms. If you find any shorted check the source resistors as well. These are the large blue .1 ohm 3 watt cement resistors.
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Old 13th February 2018, 02:59 PM   #10
Theophili is offline Theophili  United States
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thank you for your help so far! i have the power supply working again,the amp is powering up now yay!! i will order parts for the output section and go from there.
is there maybe something i can do to reduce the likelihood of this happening again,maybe adding heatsinks on the fets or transformer?
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