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Old 15th January 2014, 06:27 PM   #1
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Default M-Audio Fast Track Pro repair

Hello.
I need help in repairing of M-Audio sound card. The model is Fast Track Pro. The problem is highly distorted output. Unfortunately I couldn’t find the schematic. I measured voltages of power supplies pins of opamps. Positive seems ok (4.5V), while negative is only minus 0.8V. I attached the photo. Does the chip which I marked make negative voltage? The marking on the chip is: first line – 67351 or 6735I, second line – 95T, third line – CD8Q. I didn’t find anything on the Internet about this chip. Maybe negative supply is formed somewhere else?
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Old 15th January 2014, 06:36 PM   #2
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Just based on what you show it does look like it could be a negative rail generator as there is a coil and diode also shown. Before condemning anything make sure there is no problem on the negative rail that is drawing excess current. The diode itself could be a suspect too.

If you have a bench PSU you could try and backfeed the negative rail in situ with it all working and see if the current consumption is excessive.
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Old 16th January 2014, 06:38 PM   #3
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When I connected external negative power supply the card started to work properly. So it seems that the problem is in the part of the positive to negative supply conversion. But I cannot find what is that chip. I searched similar 8 pin convertors but those I watched had different pin location… Maybe someone knows the marking of the chip or proper analogue?
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Old 16th January 2014, 06:43 PM   #4
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So that confirms it then. Check that diode and those three electroylitic caps around it. Don't be too hasty to condemn the chip yet.
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Old 16th January 2014, 06:51 PM   #5
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The diode is ok. Will check those caps.
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Old 16th January 2014, 07:05 PM   #6
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Quote:
Originally Posted by Alexander Baev View Post
The diode is ok. Will check those caps.
The diode is a high speed type and it might not test well in circuit.

Not doubting your readings but you need to sure. Does the chip or diode get warm in use ? Can you measure a supply voltage to the DC convertor chip ?
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Old 17th January 2014, 06:17 PM   #7
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The diode seems ok. Voltage drop 0.2V. Voltages on the pins: 1 plus 5.57V, 2 plus 1.22V, 3 plus 0.2V, 4 plus 0.8V, 5 minus 0.8V, 8 plus 5.57V. Electrolytic caps are ok. I didn’t removed smd caps for checking but they are less subjected to damage. I watched the pins with oscilloscope – all voltages are constant. The chip and diode are cold.
What do you think my next step should be?
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Old 17th January 2014, 06:25 PM   #8
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If the caps and diode seem OK then the next logical step is the problem one... a new chip to try. I'm afraid I don't know what it is either.
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Old 17th January 2014, 06:29 PM   #9
Mooly is offline Mooly  United Kingdom
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Check out the TI website.

Converter (Integrated Switch) - Inverting Converter - TPS6735 - TI.com
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Old 17th January 2014, 06:31 PM   #10
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What is the voltage on pin 1 (chip enable) ?
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