Powerbass XTA500D

[Perry Babin]

Pin 16 is missing but it's probably OK. Pin 1 of the 494 is shutting down the 494. Both ICs seem to be operating normally now.

None of the schematic diagrams that I have that use similar circuits show anything other than the 293 (via 2 diodes) and a 4.7k ohm resistor connected to pin 1. Is the 4.7k resistor in the circuit and within tolerance?

 

[Perry Babin]

I found another diagram with a DC offset protection circuit. Does the amp possibly have DC offset (on the output filter inductors before the relays)?

If not, can you find the following circuits in your amp?

 

[S Merlington]

The 4.7 k Resistors is within tolerance ..

The output filter inductors have 2.12 volts on them im assuming this is whats making it protect..


I will check the diagrams..

Any ideas on what i should check to see if thats the cause of the 2.12 volts on the inductors?

The First diagram is the same as the one in this amp

 

[Perry Babin]

That's probably what's causing it to go into protect. I'd suspect either U3 or U4 on the driver board. I'm assuming that it's the 3640 but you didn't confirm that earlier.

 

[S Merlington]

yes its a 3640 board but the Audio board is out of the amp right now and its still in protection

 

[Perry Babin]

Is there possibly a solder bridge between the driver board pads? With no driver board, the outputs are typically held off and there is no DC.

If there are no solder bridges, you'll have to check all of the various components in the area of the outputs to see if you can find any that are leaky.

 

[S Merlington]

I found the Problem Q1 (A1266) was defective amp powers up perfectly now..

Thank you for the help ..

Now to install the driverboard to see if it still powers up

 

[S Merlington]

Audio driverboard installed amp powers up and idles perfectly..


Amp still has no output

Any ideas?

 

[Perry Babin]

Did you re-check all of the regulators after the accident?

Do you have rail-rail oscillation on the outputs?

 

[S Merlington]

All regulators are working correctly..

Amp has no rail to rail oscillation

 

[Perry Babin]

What is the DC voltage on pin 2 of either of the driver ICs on the 3640?

Place the black probe on the negative rail.

 

[S Merlington]

Ill get back to you on this amp since i slipped with the probe and blew 5 outputs and driver Ic's


Not my week to work on big amps i guess

 

[S Merlington]

The parts will be in later today for this amp..

I was going thru this amp 1 more time before i put the outputs and driverboard back in the amp..

ON PIN 2 i get -120.1 volts is this normal since Pin 2 is directly connected to the output leg of 2 KIA7812's ?

 

[Perry Babin]

If it's connected to the output leg and the ground leg of the 7812 is connected to the negative rail and the negative rail is at about -132v, it is normal.

 

[S Merlington]

Ok just making sure..

Wondering if its also normal not to have - 15 volts on any of the pads for the audio driverboard ?

 

[Perry Babin]

I don't see anything that needs it. I think the TL072 and the LM211 use ±5v (confirm). The LM293 uses +12v (referenced to the negative rail).

 

[S Merlington]

Amps powerd back up still no sound ..

On PIN 2 of the driver IC's I get : -122.4 volts

 

[Perry Babin]

The voltage there has to be referenced to the negative rail. What's the DC voltage with the black probe on the negative rail?

 

[S Merlington]

With black probe on Negative rail I get 0.00 volts on Pin 2

 

[Perry Babin]

What's the DC voltage on pin 1 of U6 on the driver board?

Black probe on negative rail?