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memphis audio mc1.4000 Output FET failure
memphis audio mc1.4000 Output FET failure
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Old 21st November 2017, 04:22 PM   #1
Bmwe21 is offline Bmwe21  United States
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Default memphis audio mc1.4000 Output FET failure

I have a memphis audio mc1.4000. I got it with verry cheap 80$ but someone had already removed all the power supply FETs and output FETs. After replaceing all of them with new replacements. The rail voltage is at 100v- and 100v+ at idle. The the low side out put FETS are being powered up at idle. So I replaced the ir2113s and checked the drivers for the outputs to make sure they were not shorted and they are not. Checked power on the output drivers and 1 pair i have rail voltage ( is this right for the drive transistors?) the other pair i have 0 volts. What should you see typically on the three legs of the driver transistors with the amp at idle With no audio input .

Thanks shawn
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Old 22nd November 2017, 02:16 PM   #2
MarioRestucci is offline MarioRestucci  Italy
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From Collector of mje182 to collector mje172 (for both totem pole drivers) you must have about 24v.
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Old 26th November 2017, 12:52 AM   #3
Bmwe21 is offline Bmwe21  United States
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So there is full rail voltage on all three pins and the is rail voltage on that 35v cap i circle. I replaced the failed resistor and bo change in the voltage on those transistors. Any idea why the voltage is so high and all the same.
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Old 4th December 2017, 12:05 AM   #4
Bmwe21 is offline Bmwe21  United States
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I got the amplifier working at idie or with low audio input without the power supply or the output FETs geting above 80F. As i start to turn the volume up the duty cycle to the power suppy FETs gose up and the large resistors next to the power suppy get above 400F and start to smoke. Then if you turn the volume down the duty cycle at the power supply FETs stays at the same level as it was when the volume was up even though the amp is at idle. Then if you restart the amp everthing is back to normal. What is the job of that large resistor and why do they typically fail? They are bolth 100 ohm and they are in the spec 99.7 and 99.8.
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Old 4th December 2017, 12:34 AM   #5
Bmwe21 is offline Bmwe21  United States
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Also i nocied that When you turn the volume up the transformer starts to wine then the resistor starts to get hot and even when the volume is turned down the nocie and the heat will not stop tell the amp is powerd off then back on.
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Old 8th December 2017, 08:44 AM   #6
Bmwe21 is offline Bmwe21  United States
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Is there anyone that might have some knowledge on this amp or maybe a different forum i could try? Any Thoughts?
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Old 8th December 2017, 12:07 PM   #7
Perry Babin is offline Perry Babin  United States
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Are the power supply drive waveforms good and the waveform being pulled well below 3v before they start to become more horizontal?

What did you do to stop the PS and output FETs from overheating?
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Old 10th December 2017, 09:41 AM   #8
Bmwe21 is offline Bmwe21  United States
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Thank you verry much for your time. I have read your repair tutorial and really found it helpful. I will do my best to explain the issue at hand.
1 the power supply FETs have never got above 80F at any time.
2 the power supply resistor circled in red right next to the transformer is 70f with no load and start to get over 400f under medium laod. At the same time the transformers start to make noice. After you turn the load off it continues to have the issue until the amplifier is turned off then back on. Only then dose it retuen to normal.

Iím an automotive technician and only have a slow automotive scope. Hear are some photos of patterns under NO Load.
1 power suppy FETS driver signal.
2 high and low side output FETs driver signal
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Old 10th December 2017, 09:57 AM   #9
Bmwe21 is offline Bmwe21  United States
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One other thing i nocied with no laod on the amp. There is a small transformer next to the main large ones. I dont kbow what it is used for but the rail voltage is 30v + - the small resistor circled in red is at 325F and the drive pattern for the 2 transistors that drive it is kinda odd see photo.
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File Type: jpg 90016A17-4F17-4CA0-8521-B08872CDF373.jpg (714.8 KB, 16 views)

Last edited by Bmwe21; 10th December 2017 at 10:05 AM.
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Old 10th December 2017, 04:14 PM   #10
Perry Babin is offline Perry Babin  United States
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The following diagram should be close to the basic design of your amp:
http://www.bcae1.com/temp/soundstreamxxx6500.zip

Are the capacitors connected to the overheating resistors shorted?

The waveforms in the last image are normal for a regulated power supply. Re-read section 25 on the power supply troubleshooting page and follow the links in that section.

The small transformer is for the low voltage power supplies. It's trance3 on the diagram.
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