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Old 7th May 2004, 01:15 AM   #1
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Unhappy Mini-A Help Needed

Hi,

I finished wiring up my mini-a. the voltages seemed ok, but only one channel plays loudly. By this I mean ch-1 does not produce high output. I have to put the speaker to my ear to hear anything. Ch-2 does play ok.

Could this indicate a blow or bad output MosFet?

Thanks,

Vince

CCS Ch-2

Drain= 17.27
Gate= 4.04
Source= .55

Power stage Ch-2

Drain= .01
Gate = 13.01
Source= 16.65

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CCS Ch-1

Drain = 17.15
Gate = 3.97
Source = .49

Power stage Ch-1

Drain = .08
Gate = 12.93
Source = 16.31
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Old 7th May 2004, 03:04 AM   #2
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Check your feedback resistor and resistor from the - input diff pair fet to the ground. If your offset is below .5v, The outputs are likely OK.
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Old 7th May 2004, 11:11 PM   #3
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I checked all the resistors in the front end and all the voltages on the current source and the input pair and they match the working side.

I'm only seeing .05 AC on the bad side and
the good side was showing 1.3 volts AC, with the CD player loudness at about 9 o'clock setting.

Also, the DC offset was about .01 on both sides.

Any other advice would be great.

Thanks,

Vince
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Old 8th May 2004, 02:12 AM   #4
MikeW is offline MikeW  United States
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Check to see if there is a short to ground at the input.
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Old 8th May 2004, 03:53 PM   #5
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No, input not going to ground either. It's clear.

Vince
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Old 8th May 2004, 04:28 PM   #6
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check the values of the feedback resistors and the condition of the solder joints - been there, done that.

and verify that you have a good signal going in to the "bad" channel. Done that, too. thought the amp was dead when in reality it was a bad preamp jack.
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Old 9th May 2004, 08:46 PM   #7
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Default question

Could excessive solder flux cause a short? So far, this is the only possible issue I see.
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Old 10th May 2004, 12:42 AM   #8
MikeW is offline MikeW  United States
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Check all the voltages at the input. Do Q1,2 and 3 have the same voltages as your working board. If you have a scope follow the input path until you no longer get the correct signal. I have blown up a lot of input MOSFET's.
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Old 15th May 2004, 10:12 PM   #9
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IT'S ALIVE!!!

Matched new front end fets and a new CCS and now the channel is ok!

Thing is, when I first fired it up, I saw a spark near one of the output fets. It may have been near the PS caps. I have since turned it off and on and it hasn't sparked.

Thanks everyone for your help,

Vince
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Old 16th May 2004, 11:23 PM   #10
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Default Working

How does it sound?
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