hf 1605d

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Hexhclass

Member
2010-06-22 6:08 pm
usa
D10p has a capacitor across it,any idea why that cap was install there?
The output FETs have four banks,one bank has shorted FETs due to broken legs i thinks.HIP4080 drives them,is it ok to replace only that bank?
 

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Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
As long as you keep all of the parallel FETs matched, you could probably replace only those in the group with broken legs. The exception would be where the gate leg broke, causing the FET to remain on, stressing the others in the same half-bridge. In that case, you'd need to replace all in that half-bridge. I don't know what FETs cost there but here, they're too inexpensive too risk replacing just a few. I'd replace them all in the audio circuit.

I don't know why the capacitor is there.
 

Hexhclass

Member
2010-06-22 6:08 pm
usa
I buy from them often but sometime i need to finish a repair fast and don't have
enough so i get them local.

Across the speaker terminal i see 0.543mv.I did not change all in the half bridge yet.
Could this be why am seeing this offset ?

I used IRF1010E with 47ohm gate resistor and the FETs get warm fast.Also one particular FET was heating up faster than the rest.Drive signal is clean.I try 100ohm on just that FET and it seem more stable.I don't understand why just one heat up faster.All have same date code.
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
The DC offset is controlled farther back in the circuit. If the amp produces clean audio, the DC isn't likely due to the outputs. Isn't there a DC offset pot?

Sometimes FETs will have slightly different thresholds and one will heat up more quickly. Since all are heating, the problem is likely in the drive circuit. If you have a clean signal to the gates of the FETs, there could be a problem with the 494.
 
There is a pot in the output section didn't know it was for offset.

Yes they heat up evenly but there was one FET hotter than the rest.I
installed a new 494 and drivers when i change the FETS.Will 100ohm gate resistor
be ok to used with the 1010Es?

Anyone know what the original FETs should be?
 
I don't know if the 100 ohm resistors would be good for the 1010. Generally lower values will make the FETs run cooler.

I generally use the 3205s in these amps with 47 ohm resistors.

I don't know what the originals were.

Is the oscillation frequency at the FETs in the 25-30k range? Sometimes the frequency goes too high and causes the FETs to run hot when there are no other problems.

Is the amplitude at the gates approximately 10v?
 
On the gate i see 39.35khz,
On the drain 31.39khz.One the drain of the FETS on the other side of the sink i see 79.86khz.
Source leg is78.86khz

If i touch pin 4 of the 494 with my probe,I hear squeel noise and amp will start to draw excessive current.

10v/dv 10/us for the gate wave form and 5v/dv for pin 5 of 494
 

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