Hifonics HFI3000D

[scotts530]

I'm working on a Hifonics HFI3000D, So far I've replaced the power supply fets ( IRFP064N ) and all 47 ohm gate resistors. The resistors i ordered were a different type of resistor that was in it I'll post a pic. I have also removed all of the( IRF9640 ) in the output side 3 of them were bad. Should i replace all the gate resistors or just te ones out of tolerance. After that is there anything else i should check before putting it back together and testing it?

 

[Perry Babin]

At the very least, you should replace all of the gate resistors that are for the FETs in the parallel group of FETs that had damaged resistors.

 

[scotts530]

Here is the pictures

Here is the pictures

 

[twilliar]

Do you know the original cause of the amp failure? Also, are those 47-ohm resistors carbon resistors? Caution with those if they are as the resistance value is unstable under temperature extremes and over time.

 

[scotts530]

I'm going to replace the 47 ohm resistors with tv's exact kind that came out of the amp. Why is there two resistors for each output transistor

 

[twilliar]

Depends on the amp but the first scenario that comes to mind is the pulldown resistor when you see resistors across the gate and source to keep it off.

I hope that came out right!

 

[Perry Babin]

That's right. The high value is pulldown. The low value is the gate resistor that the FET is driven through. See attached.

 

[scotts530]

So the 100k resistor is the pulldown and the 10 ohm is the gate resistor?

 

[Perry Babin]

Yes

 

[scotts530]

I replaced all power supply fets and gate resistors and all 8 of the IRF9640 in the output along with the gate resistors and all the pulldown resistors. I put the amp back in the case and clamped everything down and attempted to turn it on with a15 amp fuse inline and the redlight will come on then goes green then pops the fuse.

 

[Perry Babin]

Not all of the outputs were 9640s. Did you use 640s and 9640s or just 9640s for all output transistor locations?

 

[scotts530]

10 fets the ones i replaced were 9640 the other 10 fets are 640n they all check ok

 

[twilliar]

Is that the output drive board with the two 21844's with U4D's next to them?

 

[Perry Babin]

The 21844 amps use all N-channel.

Since the outputs are already installed, the simplest way to test may be to remove the rectifiers. Then see if it draws excessive current.