Viper (Directed) d1200.1 Supply Fet Problem

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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!
 
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?
 
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
 
Perry Babin said:
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 !:)
 
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.
 
It sounds like the transformer may be shorted. With a current limiter in the B+ line... did you try twisting, pushing, pulling the transformer while it's trying to draw excessive current to see if the current draw changes?

As was mentioned above, an automotive headlamp (i.e. an H6054 using the high beam filament or both filaments in parallel) or a 2 ohm current limiting resistor (a 2 ohm dummy load resistor if you have one) can serve as a current limiter.

If the amp failed due to reverse polarity, you could suspect the driver IC but if you have a clean square wave on the gates of all of the power supply FETs, the driver IC is likely OK.

Have you checked the board for shorts between pads? Often a tiny piece of solder bridged between pads can cause this sort of problem.
 
What exacaltly are you referring to as "Pads".

If you are meaning the semiconductor "Pads" to heatsink

I have the circuit board removed heatsink.


I have current limiter for B+ on bench that I can use for initial testing

I'm thinking transformer as well,no short found,and power supply power isnt intermident .Its a constant linear fault.


Thanks for any and all input...
 
thanks for the definition.

Tobe!

Next step is to remove primary transformer input taps from one side of bank to verify primary to primary short.

If that doesnt work moving on to secondary....

But I would like to be talked out of it.....

Hurry up everyone.... Children are driving me crazy(2&3year old):bawling:
 
I fully agree with Perry.
The problem sounds like a short transformer (primary or secondary).
Once the transformer has been uninstalled, check that there is no short circuit between primary and secondary.
It is really difficult to see if there are short circuits between primary and primary, or between secondary and secondary, because with a normal multimeter in diode test mode, you will not be able to figure out if there is a short on that line, because the primary winding (also the secondary) is continuous, so you'll be short.
You would need an inductance meter. But unfortunately it is not a common tool.
If anyone knows a method to find a short on the transformer, which I do not know, I'm grateful. Unless the short circuit is visible to the naked eye (for example, a visible burn on the winding), I think the only way is to rewind the transformer.
 
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