Viper (Directed) d1200.1 Supply Fet Problem - diyAudio
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Old 31st December 2008, 08:28 PM   #1
amc32 is offline amc32  United States
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Default Viper (Directed) d1200.1 Supply Fet Problem

I have repaired this amp once before"output only". Now its back! Power Supply is shot, 6 HUF75343G3 55volt 75amp .0009ohm.

Pulled them all out to verify PWM is working,its ok. Replaced Fets with IRP064N looked like a good replacement,needed something alittle more robust.

Installed Fets in Supply with rectifiers removed.Amp powers up and down in a very linear switch mode will pulling excessive current.

Should I replace the good gate resistors to another value.Present resistance is 22ohm maybe 47 or 100....


Any input would help!
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Old 31st December 2008, 10:09 PM   #2
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Without the rectifiers in the amp wouldn't this blind the PWM feedback to any output and thus cause the over-current condition ?? Just asking cause I rarely pull rectifiers unless they are bad.
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Old 31st December 2008, 10:25 PM   #3
amc32 is offline amc32  United States
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Thought to remove them to verify Power Supply was operating properly.Rectifiers are not bad though.I will reinstall for the sake of it though.

Just wondering if theres anyone with a MA Audio 4000K apart,need gate resistor value....
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Old 31st December 2008, 11:11 PM   #4
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Removing the rectifiers is a good way to disconnect the audio section from the power supply to determine if the excessive current draw is due to a problem in the PS or audio sections. I can't remember any time that it's caused any problems.

22 ohm resistors are OK.

Are all of the FETs in the supply heating up?

If you have a scope... On the falling side of the gate drive waveform, is the waveform perfectly vertical down to at least 2v (check all gates)?

In the MA audio amp, didn't at least 1 or 2 survive so that you can get the value?
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Old 1st January 2009, 12:57 AM   #5
amc32 is offline amc32  United States
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No Fets are heating up....
Its just switching,but abnormally.....no heat...

Maybe not switching on and off at the right times ,maybe core saturation

On the scope without Fets clean lines,
With Fets it looks clean powering up momentarly until protection shuts it down. Then it powers up again. And it just keeps on cycling.
TRansformer is buzzing during this abnormal cycling...
Pulling current very quickly though,,,,no heat
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Old 1st January 2009, 01:03 AM   #6
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Can you send me a photo of the inside of this amp?

babin_perry@yahoo.com
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Old 1st January 2009, 02:02 AM   #7
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Quote:
Originally posted by Perry Babin
Removing the rectifiers is a good way to disconnect the audio section from the power supply to determine if the excessive current draw is due to a problem in the PS or audio sections. I can't remember any time that it's caused any problems.

I wouldn't try this on any MS series PG amps or with any amp that uses complex opto-coupler type feedback for amp protection. All these amps use balanced DC rails to turn on a opto-coupler with zener regulated DC voltage drop so a acknowledgment signal gets feedback to the PWM that the power supply is functional. If not the supply usually faults for what appears to be no good reason at all.
So although I agree diode removal won't hurt anything, it can cause misleading symptoms that tend to cause confusion of the original issues, and unless the diodes are bad it can be a waste of time.
But here again I also rely heavily on a current limited power supply method of bench testing. Once you set your current limits on the bench supply nothing gets damaged as the 12 volt source will knuckle over into current limit at a very safe region and the amp under test will just shutdown as the 12 volt feed drops to zero.

I just can't see pulling things apart that are completely functional to begin with so I developed the above method rather then spending all that time pulling out perfectly good parts. It just seemed logical that if its not broken then don't fix it.
Happy New Year everyone !
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Old 1st January 2009, 12:23 PM   #8
djQUAN is offline djQUAN  Philippines
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well, one could say that not everyone has a current limited supply....... but a car headlight in series with the B+ line would work just as well.
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Old 1st January 2009, 01:27 PM   #9
amc32 is offline amc32  United States
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Ok here's the update.

Reinstalled Rectifiers with Fets installed,same problem
" " " with only one pair Fets installed,same problem

" " with Fets removed,rechecked PWM 5volts square


Reinstalled Rectifiers with substitute Fets in Supply (Buz10,IRFZ44) just to verify if IRP064N is a bad substitute for HUF75343G3.
Buz10 went up like a candle before my eyes....

B+ Caps & B+ bypass Caps all good.....
No shorted diodes


Maybe this will help! Customer did admit that he had installed Power and Ground backwards on this amp,on a reinstall into new car.
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Old 1st January 2009, 01:51 PM   #10
amc32 is offline amc32  United States
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Checked transformer in amp for shorts. Nothing...............

This is suppose to be a level 1 repair: Shorted Diode and maybe some Fets and drivers.....

Need to get this one off the bench,got several Orions 2250 to rebuild.
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