earthquake 200dhc-mark2

[RockfordFIx]

Here is pin 8 of the njm3403 with no input signal

 

[RockfordFIx]

This pin 9 ad pin 10 of njm3403

 

[Perry Babin]

#38:
That's the rail-rail voltage. The rail voltage is on the center leg.


The rest are about what I'd expect but there may be a bit too much carrier on pin 8.

Does the amp produce any output with pins 8 and 9 bridged?

 

[RockfordFIx]

What would cause too much carrier signal?

 

[Perry Babin]

I looked at it again and it's not carrier (which would be in the 80kHz range) but it should not be there.

I wanted pins 8 and 9 shorted to eliminate the feedback from the signal and I wanted signal driven into the amp (would be seen on pins 8, 9 and 10) to see how the IC reproduced that signal. It wouldn't be clean but the output that it produced may be able to point us in the right direction.

 

[RockfordFIx]

When shorting pins 8 and 9 I have no waveform on pin 10 or pin 8 or 9. I did try jumping pin 1r to pin 10 because I had audio signal there. That immediately producing a 60hz square wave. If I run a jumper wire from rca signal to pin 10 I get no waveform. With no signal and pin 8 and 9 shorted I have 6vdc on the speaker terminals

 

[RockfordFIx]

I tried taking the audio from pin 14 to pin 10 and that produced a square wave at 60hz

 

[Perry Babin]

Was the square wave at the speaker terminals?

 

[RockfordFIx]

There is no waveform on the speaker terminals

 

[Perry Babin]

Post #17:

At what point was the square wave produced?

 

[RockfordFIx]

Audio from pin 14 was fed into pin 10. Pin 8 and 9 now have a square wave and and square wave on pin 7 of the 4080

 

[Perry Babin]

Are the output in the amp?

Is the 4080 in the socket?

 

[RockfordFIx]

All outputs are on circuit and the 4080 is in the socket

 

[Perry Babin]

Is the relay closing?

 

[RockfordFIx]

Relay?

 

[Perry Babin]

That's right. Earthquake doesn't use one.

Post the signal you now have on 5, 6 and 7 of the 4080.

 

[RockfordFIx]

Hey perry is it possible to power the amp with the 4080 removed. I can’t seem to find this signal problem on this amp. I also can’t seem to get the dc offset control to work either.

Will removing the hip4080 break the feedback loop? Still trying to isolate why signal going to the 4080 is distorted

 

[Perry Babin]

It depends on the version. Post a photo of the output FETs and the surrounding area.

 

[RockfordFIx]

Hey perry,

Here are the pics of the board.

 

[Perry Babin]

That one has no pulldown resistors. You have to add one per bank. Virtually anything between a wire jumper and a 100k will generally work. Solder the resistor between the gate and source legs of the output FETs. It doesn't matter which of the 3 in each bank you solder to. 4 resistors total.

When you power up, make sure that none of the FETs are getting hot and the current draw is nothing more than normal idle.