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Old 26th November 2009, 12:42 AM   #1
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Default precision power A800/2 (blown transistors)

can someone tell me what am i looking at..?

are these output transistors or powersupply transistors?

nevertheless, five of them have blown.. as can be seen by the picture below:

Click the image to open in full size.

it looks like one resistor is definitely burnt.. possibly a second resistor.
do you think one or two of these need to be replaced also?

Click the image to open in full size.

Click the image to open in full size.

will replacing the five transistors with the exact same part number get this amplifier back to an operational status?

links to the transistor are here:
http://www.fairchildsemi.com/ds/FQ/FQP50N06.pdf
Product Folder - FQP50N06 - 60V N-Channel MOSFET QFET

more pics of the damage are here:

Click the image to open in full size.

Click the image to open in full size.

i took the amp out of the trunk and connected it in the house.. the amp lit up right away.

...replacing those 5 transistors and the resistors close-by is all i need to do yes/no?
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Old 26th November 2009, 01:00 AM   #2
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Join Date: Dec 2005
Location: Northern California
Power supply mosfets and I would replace them all from the looks of the amp, and any of the gate resistors that burned up also.

I would also ohm out the other devices attached to the sink to see if any of them are shorted out also...

Usually a channel must blow or something else may have been shorted to cause this sort of failure...that is just my opinion though and you might be luckier then many others I have seen over the years.
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Old 26th November 2009, 01:21 AM   #3
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no, no, no,

i had a channel blow.. there was a constant screech when i hooked up a speaker.

then i put my radio up for like an entire year.. never put the faceplate of the radio on.

i brought the amp into the house to test the blown channel and make sure the amp channel was indefinitely blown.
but the wierdest thing happend.. i couldnt get any output from EITHER channel.

last time i had the amp hooked up in the car, the one channel was working fine and i had ran two 5.25inch midranges on the one remaining channel.

i have absolutely no idea why the other channel quit working.
and i'm also baffled that the known broken channel didnt screech when i had it hooked up in the house.

if i have output transistors that are also fried, i think i'm gonna use my square trade warranty.
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Old 26th November 2009, 01:35 AM   #4
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Join Date: Nov 2003
Location: Louisiana
It probably screeched in the vehicle because you had a shorted speaker wire (shorted to chassis ground). Moving it to the other channel moved the shorted wire from an active output (one with signal) to the grounded speaker terminal which would typically cause nothing more than engine noise.

After removing the 6 FETs and checking the gate resistors (as was previously suggested), you need to check the gate drive signal. Measure the DC voltage on the output pins of the driver IC (SG3525 or TL494?). The voltage on the gate pads (the solder pads where leg 1 of the FET solders to the board) for the power supply FETs should essentially have the same voltage (~5-6v).

After replacing the FETs and before applying power, clamp all of the components on the heatsink tightly down and insert a 10 amp fuse in the B+ line. This will help protect the new parts if there is another fault.
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