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Possible substitute for STP80N70F4
Possible substitute for STP80N70F4
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Old 19th September 2018, 03:18 AM   #11
mild2wild is offline mild2wild  Trinidad and Tobago
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Join Date: Nov 2014
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...
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Old 19th September 2018, 03:56 AM   #12
Perry Babin is offline Perry Babin  United States
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When one rail increases when driving a load, it's generally an indication of a driver problem. If the negative rail is increasing, the problem is most likely a problem with the drive for the low-side FETs.
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Old 19th September 2018, 04:18 AM   #13
mild2wild is offline mild2wild  Trinidad and Tobago
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Thanks for the reply. That is what I figured so I changed all of the driver transistors and all of the transistors on the driver board. What else should I check or change?
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Old 19th September 2018, 04:51 AM   #14
Perry Babin is offline Perry Babin  United States
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Look at the drive signals. Are they of sufficient amplitude (generally about 10v)?
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Old 24th September 2018, 06:20 AM   #15
mild2wild is offline mild2wild  Trinidad and Tobago
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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?
Attached Images
File Type: jpg IMG_20180924_011304.jpg (629.7 KB, 41 views)
File Type: jpg IMG_20180924_011255.jpg (329.7 KB, 42 views)
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Old 24th September 2018, 01:53 PM   #16
Perry Babin is offline Perry Babin  United States
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Are the FETs in or out of the circuit?

What signal were you driving into the amp when checking for drive?

Post photos of the positive drive signal with both AC and DC coupling.
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Old 24th September 2018, 02:04 PM   #17
mild2wild is offline mild2wild  Trinidad and Tobago
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Join Date: Nov 2014
The FETS are in the circuit. There was no signal being driven into the amp. I will post AC and DC coupling photos.
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Old 24th September 2018, 05:17 PM   #18
mild2wild is offline mild2wild  Trinidad and Tobago
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Join Date: Nov 2014
I don't think my USB scope can do AC coupling, it is a Hantek 6022BE. I see no option for coupling and Google searching lead me to this conclusion.
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Old 3rd October 2018, 06:06 PM   #19
mild2wild is offline mild2wild  Trinidad and Tobago
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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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File Type: jpg IMG_20180924_123438.jpg (943.7 KB, 13 views)
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