AUDIO SYSTEM ADS 12002 failed repair attempt - help needed!

[coolnose]

Hi All,

I have (at least tried) repaired a ADS 12002 2-channel amp.

It had fried the power supply fets.

Original Fet were ST 50N06 and I replaced them with Fairchild FRP50N06.

Resistors (10 Ohms & 4.7kOhms) and caps (10nF) were replaced with original values.

The only change to the original is that I replaced the 2 big 15 Ohms restistors (R85 & R86) after the transformer with 22 Ohms, the closest value I had on hand.

Diodes measure OK, so do the drivers and the Outputs.

The amp is blowing his 10A straight on turn on.

I'd need some guidance on how to proceed further.

Cheers,

Max

 

[mbates14]

check the outputs, probably shorted.

 

[Perry Babin]

Does it blow the fuse with no remote voltage applied?

 

[coolnose]

Does it blow the fuse with no remote voltage applied?

Hi Perry,

sorry, I wasn't clear on concerning that point.

The fuse blows immediatly when then remote voltage is applied, no problem when hooking it up.

I am having a hard time checking the darlingtons in-circuit, should I take them out ?

Cheers,

Max

 

[Perry Babin]

What do you mean when you say that you're having a hard time checking them?

If they're defective, they will likely have very low resistance between the three legs of the transistor. Do you have any that read anything near 0 ohms?

 

[coolnose]

When checking them in-circuit, I have no lower resistance than 3.6k ohm (worst case) in any pin combination both on P and N outputs.