Xtant 403A not powering on

[DiyFan]

No I don't have a replacement. What is its function in the circuit?

I have a limited assortment but no surface mount resistors.

 

[Perry Babin]

If you have something near 1k ohms, connect it in series with the cathode. Short the cathode and reference. Connect the resistor's free end to a 12v power supply. Connect the anode to the 12v PS ground.

What's the DCV from anode to the cathode/reference node?

It's used in the bias circuit.

 

[DiyFan]

I pulled the TL431 and did the test. I measured 2.5vdc A to bridged C/R so it seems to be working correctly. Soldered it back in and still am only measuring -.18vdc A to R.

 

[Perry Babin]

There appears to be an defective component. The 10 ohm resistors were the most common. You'll need to do it the hard way and check all of the small components.

These amps are not like most others in that you can't remove the smaller transistors and power up. For most amps, it won't cause a problem. In these amps, it can cause excessive current draw.

 

[DiyFan]

Thanks for all of your help Perry. I did find a partial schematic you posted of the 603A amp that seems to be similar if not the same as this amp. I will use it to help and test all the individual components and report back. Thanks again.