Hifonics NX750D Curse

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mbates14

Member
2002-06-02 2:14 am
non
Speaking of HIP4080 and the curse, I ran into a NX750D. Blown outputs.

Replaced all the outputs with IRF3710Z, and a new HIP4080.

All i get is a loud white noise from the output coil.

Some quick scope shots determined the gate drive going to one-half the outputs is nothing but biased noise.

Further checks on the input side of the HIP4080 +IN pin is nothing, which its supposed to be the oscillator.

The oscillator isnt running. Any ideas? Sometimes the amp will power up with no noise at all, but either way the oscillator is not running.

I see a CD4013 D-type flip flop which I assume is the oscillator? voltages are present but no oscillations. Nothing on the clock input, which appears to come from the LM393 IC3C

I am at a loss. any ideas?
 

mbates14

Member
2002-06-02 2:14 am
non
Yes, everywhere. And I checked those. Also, checked the voltage regulator transistor that feeds the 12V into the 2 LM393s, and the other one which I cant remember the number off of.

See, Now im cursed. I never really had any issues with HIP amp rebuilds, except for this one. lol. In your professional opinion, Why are these things so horrible? Is the HIP chip not suited for the task? or some other unknown intity.

Anyway, the LM393 that appears to be the oscillator, appears to be setup as a VCO. and its control voltage comes from 2 other op-amps and an adjustment pot. The reason the oscillator isnt running is becuase the control voltage is all the way up to 12V.

If i pull the other 2 op-amps and leave only the oscillator, the oscillator will run again. But its stuck in protection because of the other 2 op-amps not being there.

Only thing I know to do at this point is re-op-amp the thing with new ones.

I cant sub in an NE5532 or a TL072 in place of the LM393, it doesnt work. My guess is because the LM393 is single supply.
 
I cant sub in an NE5532 or a TL072 in place of the LM393, it doesnt work. My guess is because the LM393 is single supply.

The LM393 is a Comparator not an OpAmp. OpAmps and Comparators can not tell if you are running Single or Split supplies. I am guessing the LM393 is doing some kind of duty cycle modulation of the power supply, it would not be used as an Oscillator. The NE5532 and TLO72 are OpAmps.
 

mbates14

Member
2002-06-02 2:14 am
non
BTW, Perry Babin is around, but hes extremely busy and hasnt signed into the site because of it.

I appreciate the fact that he brings free help with nothing in return.

He pretty much told me ZD1 was bad, 6.2v Zener. Measured in circuit, it was fine. But little did I realize, soon as I removed it, it read OPEN. Replaced it and all is well.

protection circuit was a little picky and didnt want the amp to power up at times, replacing C2D 47uf 16v solved this.
 
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