Possible substitute for STP80N70F4

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Blown Hifonics BRX2000.1D repair

Did a search and could not find anything about this FET on the forum. I am repairing a Hifonics BRX2000.1D Brutus amplifier and the PS FETS need replacement. There are 12 STP80N70F4 transistors in the power supply. I am not finding them listed at any of the reputable suppliers, and the local shop says they have them but at a ridiculous price. Is there any other FET that can be used in place of this one which may be on hand, cheaper, or more easy to get? Thanks in advance.
 
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So, I have the power supply up and running after installing IRF3205 with 47 ohm resistors, A1275 and C3228 driver transistors and nearby resistors. I am getting +-62v rail voltage when the amp is powered up. All 12 IRF640 outputs are currently removed.

The problem is that the amp is going into protection. If the driver board is not installed, the amp will power up briefly, but will go into protection after the relay turns on.

PROBLEM 1
If the 100 ohm pulldown resistors connected to the gate pads of all 6 positive outputs are lifted, the amp will idle without going into protection as there is 0v on the output pads. When all 6 100 ohm resistors are connected there is 4.3v on the speaker terminal pads of the output transistors. As each pulldown resistor is added or removed there is a change of approximately .7-.8v on the output pads.

PROBLEM 2
There is 75.6v on the gate pads of the positive output transistors. The negative output pads appear to be what I would expect to be normal. I would think that there should be 60-61v on the + output gate pads. According to what I read in another thread, the 80.5v on L7815A gate seems to be normal.

POSITIVE OUTPUT TRANSISTOR PADS
Q204 and all others: 75.6 61.5 -0.00
NEGATIVE OUTPUT TRANSISTORS PADS
Q222 and all others: - 61.2 -0.00 - 61.7
POSITIVE REGULATOR:
L7815A : 80.5 61.5 76.0
NEGATIVE REGULATOR:
L7812 : - 42.4 - 61.7 - 61.7

Do I need to change the positive regulator?
Is the positive regulator responsible for the high gate voltage on the output gate pads?
Why is there 4.3v on the output terminal pads when the pulldown resistors are connected?

I haven't even gotten to the driver board yet, but I believe this Amp should idle without protection when the driver board is removed.
 
Oops, I meant 100k ohm pull down resistors.
 

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So I discovered a shorted C2690 driver transistor. I replaced all four C2690 and four A1220 driver transistors. I also replaced all of the 1d and 2d transistors on the audio driver board and all 12 IRF640N transistors. The amp Powers up and idles at approximately +/-64v rail voltage with minimal current draw without a speaker or load connected. As soon as a speaker is connected, the negative rail starts to creep upwards.

The amp was repaired at this same state just before the replacement of all these parts, but when tested in a vehicle, one of the negative rail caps vented through the top so I assume the problem was existing at that time also.

What can I check next? The only other thing I read about in other Hifonics threads was replacement of the TL072C opamp on the audio driver board...
 
I checked for gate drive on the outputs. The positive rail outputs have a drive signal while the negative outputs do not. The screen shot is attached below. The scope is set to 20us 5v. Where can I track down the missing negative gate drive signal?
 

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I swapped out the power supply driver board just to be sure that is not the cause and the problem remained the same. I am posting scope shots of the power supply gate drive signal just to be certain that is OK.

I swapped out the audio driver card and the problem remained the same also, so I am stumped here.

Any suggestions on what to try next?
 

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Does anyone have any suggestions as to what I can check or change next to solve this issue?

The amp powers up and idles at 62v of + and - rail voltage, but as soon as a load is applied to the output terminals, the - rail voltage starts to increase.

I have changed ps transistors and drivers, output transistors and drivers, ps and output driver boards, and the problem still remains. I do know that there is a problem with the bias or negative output gate drive signal, as there is no gate voltage on the gate leg of any negative outputs, while there is 1.85v on the gate leg of the positive outputs. I took a measurement from a similar amp using the same driver board, drivers and outputs and in that amp, there is just a little under 4v on the gate leg of both negative and positive outputs.
 
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