Earthquake PH-D3 problems

[ultra]

Got this amp for repair. I am the third guy attempting to fix it.

Came to me in a really bad condition with almost everything on it fried.

I started from the power supply, replaced 3525, Dual gate driver chip,

and since i coulnt find the original STP80N06, i used IRF3205.

In the class D section HIP4080 was replaced, a few zeners,

a few burned resistors, but when i came accross with NTP52N10 fets, i almost gave up.

But then i remembered Perry Babin's suggestion of using IRF3710Zs.

I knew the power supply was ok, so upon powering up, everything seemed ok.

Nothing was hot either on the PS oe at the class d.

There were 53mV DC at the output terminals, that dropped to 51mV DC with a load connected.
Upon connecting a 100Hz signal from the generator,

and seeing it amplified at the output, i clamped everything back to the heatsink.

Now, it produces audio fine, but at a certain point there is some crack, like the sound is badly distorted.
I cannot turn up the volume.
So i started looking everything from back to front when i noticed that the output filters were hot.
Actually the wire ups in one of them had discolouration from the heat.

Is it possibe that the chokes are bad and the problem is there?

They both measure 48μΗ on board.

Also there is trimmer close to a photo resistor at the preamp section of the amp.What does this do?
Does it have anything to do with the distorted sound?

[Perry Babin]

Is the B+ voltage remaining at or above 12v?

Are the inductors operating at the same temperature if the amp is left to idle.

Are all of the parts in the board?

[Dr Zeus]

What kind of battery/power supply are you testing this amp out with? I noticed something very similar while repairing a Mmats 1400 - it was a little tempermental on a 20A power supply. As soon as I put it on a 60A supply, it was able to produce a lot more volume without cracking the subs. When my Mmats 'cracked' on the 20A supply it was almost like straight DC was pulsing the test speakers. The chokes may be seeing too much DC.

Try a larger power source? Perry is dead on - you should monitor B+ for voltage drop. These type of amps appear to have bad tempers below voltage.

You could also have a combination of bad outputs and a bad 4080.

[ultra]

Everything is clamped to the heatsink.
Both inductors have the same temperature
No voltage drop at 12V.
I do have +82V constantly at the secondary,even when this "crack" occurs.
The power supply is 68A as well as a 164A if needed.
All the parts i used are original from Farnell.
However, i ve heard that the previous owner abused this amp by replacing the 20A
speaker fuse, to a 30A. When he did that, a 2W resistor at the output filter was overheating, so he replaced it with a 5W.
I do have the schematics if needed.

[brandes.cm]

Do you have a scope? Monitor the opamp section and look for the distortion there. You could eliminate one section at a time.

Sent from my DROID using Tapatalk

[Perry Babin]

You mentioned the IRF3710Z outputs, are you using the Z version?

This is very similar to what you get when you use incompatible outputs in these (4080 based) amps.

[ultra]

Yes definitely. IRF3710Z is what i used

I also have a scope etc.

Thanks for replying so far.

[Perry Babin]

If you drive the amp to hard clipping with no load, does the amp draw excessive current or shut down?

[ultra]

Just tried it. No exessive current, no shut down.

[Perry Babin]

Although it's a bit risky and you'd have to be careful, you may want to try disabling the protection circuit to see if the problem is with the output stage or with the protection circuit.