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Old 3rd August 2012, 10:58 PM   #1
bitpoop is offline bitpoop  United States
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Default rock fosgate 250 a2 help.

on my 250 a2 I would like to know how to check the fet's
I have a ohm meter, the amp has several different fet chips.
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Old 4th August 2012, 07:25 AM   #2
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Read both the Basic Amplifier Repair page and the Basic Transistor Testing pages (link in sig line below).
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Old 4th August 2012, 07:14 PM   #3
bitpoop is offline bitpoop  United States
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thanks for the link. looks like every fet chip in the amp is shorted.
the left side matches the right side for shorts,- like u 1620 leg 1 and 3 short on both sides.
I can get most of the replacement fet chips on ebay, but I cannot find U1620.
is there a replacement chip for u1620?
for 5NO5HD, I was told to use irf 3205 - is that correct?
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Old 4th August 2012, 07:29 PM   #4
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Don't buy semiconductors from ebay. There are too many counterfeit parts being sold there.

Buy from digi-key, mouser, arrow or future electronics.

The rectifiers appear shorted because the outer legs of the rectifiers are connected across the transformer windings.

The IRF3205s are generally good substitutes for the power supply FETs. If the gate resistors are greater than 51 ohms, replace them with 47 ohm resistors.
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Old 4th August 2012, 08:25 PM   #5
bitpoop is offline bitpoop  United States
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thanks perry, if u need car help send me a message.
most people never change the power steering fluid on there cars,
u can tell by smelling the fluid it will smell burnt when bad.
the same with rear axle drive cars, people never change the gear oil. (every 15k miles)
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Old 5th August 2012, 12:25 AM   #6
bitpoop is offline bitpoop  United States
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the gate resistors r150,r152,r250,r252
all are 12 ohm's
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Old 5th August 2012, 10:25 AM   #7
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I should have been more clear. I was referring to the power supply gate resistors. They are R19 and R20. They are likely 68 ohms.
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Old 5th August 2012, 06:50 PM   #8
bitpoop is offline bitpoop  United States
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ok the gate resistors r19 = 68.1 and r20= 67.7.
can i test the rectifiers on the circuit board or do they need to be removed first?
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Old 6th August 2012, 03:17 PM   #9
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The rectifiers can be checked in the circuit. If you don't read anything near 0 ohms between the center leg and the outer legs, they are likely OK.
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Old 6th August 2012, 07:36 PM   #10
bitpoop is offline bitpoop  United States
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rectifiers I count 6 - 3 on each side.
they all read n/a on ohm's with any leg combination.
I have not done the test with a diode tester yet.
what I don't under stand is, when i test for ohm's the meter jumps,
for a split second then goes to n/a?
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