Directed 750 D

[mike49504]

I got this amp in for repair and resoldered the pads on the 2 boards in the amp for the gain and crossover.

Amp powers up and plays but the gain control and the switches do not work in this amp.

It only plays full range music and cant get the gain control or any switch to work.

Wondering what might cause this?

 

[Perry Babin]

Master/slave switch?

 

[mike49504]

Tryed the also and amp will only play full range

 

[Perry Babin]

Can you post a photo of the preamp section of the amp?

 

[mike49504]

Perry,

Heres the pics of the preamp and output section I still cant figure out why the switches/pots do not work

 

[Perry Babin]

If you drive a sine wave into the amp and measure the AC voltage on the pots in the amp, do you have varying voltage on any leg of any pot?

 

[mike49504]

Both pots have varying voltage on them

 

[Perry Babin]

Do any terminals of any switch have varying voltage on them?

 

[mike49504]

All switches have voltage on them but not varying the volte stays at 1 spot

 

[mike49504]

Any thoughts on this amp?

Pots have varrying voltage on them Switches have voltage but the voltage is not varying

 

[Perry Babin]

On the defaced IC closest to the potentiometer, there should be signal on pin 3. You'll have to follow the signal back from there to see where it goes. The next connection back down the line is likely an op-amp (or two). You'll need to follow it back until you come to a circuit that has both a varying and a non-varying voltage.

I'm assuming that you've examined the board and haven't found any jumpers, solder bridges or broken connections.

 

[mike49504]

I had this amp fixed and gave it back to the customer.

He brought it back today with a differnt problem.

If i hook up power and ground its fine.

If i hook up power,ground,remote, it draws excessive current. I checked the outputs all seem to test fine checked power supply fets all seem good.

The inductor looks like theres some white residue in the middle of it not sure if that normal?

Wondering where do i start checking since this thing draws excessive current

 

[Perry Babin]

Did you check them thoroughly (1-2, 1-3 and 2-3)?

Was the residue there when you last had it open? If you don't remember, maybe you have a photo of it.

 

[mike49504]

I checked them 1-2 1-3 2-3 all seem to test fine . Maybe one may be leaking ill check that first. I dont remember if the white residue was there or not. I will look to see if i have a pic of the amp the first time it came in.

 

[mike49504]

If i take the outputs out of the amp it powers up fine and relay clicks on.

So i replaced all outputs with new one's. Tryed powering it up and it draws excessive current again.

Wondering where i go from here??

 

[Perry Babin]

If you power it up through a current limiting resistor, do the outputs get hot?

 

[mike49504]

Yes outputs get hot

 

[Perry Babin]

Did you ever get a new scope?

 

[mike49504]

I have a scope here that works .

 

[Perry Babin]

Remove the outputs and measure the DC voltage on the outputs of all of the op-amps. Which one has ±15v on the power supply pins and more than a fraction of a volt on the output?

How much voltage?

What's the DC voltage on the inverting and non-inverting inputs for the op-amp with significant voltage on it's output?