Audioque amp problems

[Zookz]

I have an Audioque 2200.1D V2 amp. It powers on and has the green light with no excessive current draw at all. When I apply RCA's from my tone generator and turn it on and output a signal into the amplifier (with no speakers connected) it will have not only the AC voltage on the speaker terminals, but also have DC voltage. If I turn up the RCA signal and make the amp output around a few volts DC it will go into DC offset protection. If I leave the input signal down and the output on the terminals at around 1Vdc or so it will stay powered on. If I connect a speaker it will hum until you turn it up and it protects. It outputs DC and AC voltage so I'm still getting the audio signal through. All output FET's seem good with no shorts. Any help would be great!

 

[Perry Babin]

Q7, 11, 19 and 22 commonly fail. They can fail in several ways (leaky, open, shorted) so you have to either replace them or check them carefully.

I'm assuming that this is the 2610 driver board.

 

[Zookz]

Thanks, Perry. I removed all four of those transistors and checked them and they are each still working. Would you care to share what a replacement part number would be for those for future reference?

 

[Perry Babin]

The SMD Code Book

1D = MMBTA42
2D = MMBTA92

If you can find no other problems, replace them. Sometimes transistors that are run hot can have intermittent internal connections.

 

[Zookz]

Thanks for the resource! I have MMBTA42's on hand but I do not have any MMBTA92's. I do have some MMBTA56 and MMBTA92LT1. Would either of those be ok to use?

 

[Zookz]

Also, what else should I check or look for? The power supply is perfect and I believe it's on the audio side. I did test the voltage regulators and the 15V regulators are fine but one of the 12V regulators is reading normal and the other has around rail voltage on two of the legs somehow.

 

[Perry Babin]

These are the only components that I've seen cause the fault you described.

Why won't the MMBTA92s that you have work?

 

[Zookz]

I thought that the ending numbers may make it different. I will replace those and see what happens.

 

[Zookz]

I just replaced those four transistors on the output driver board and the amp is doing the exact same thing. When I pulled all four transistors they checked good and the new ones did as well. What else could I check?

 

[Zookz]

I decided to take the board out to do further testing and as I was sliding it out of the case I noticed that all four rectifier diodes on the board (FMU32U) had broken legs in the same spot. I'm not 100% sure if this happened when I was sliding the board somehow, or if it was previous. They made a clean break and when I slid the board back over them they were actually making contact barely. Anyways, now that the board is out and I put the diodes back in place I cannot replicate the issue with this amp. It outputs a clean AC signal and no DC now. Could the diodes have caused the amp to still be able to turn on and output an AC signal but also pass DC if one leg wasn't connected or something?

Should I put the amp back in the case and install all of the heatsink clamps again and test it. If it works fine should I consider the amp "fixed"?

 

[Perry Babin]

The broken legs were likely making an intermittent connection. If one rail was intermittently supplying voltage to the amp, that could have caused the problem.

You should check the legs of the other components to see if any are weak. If so, you may need to make some sort of support to keep the legs from breaking again.

When you get it back into the sink and everything clamped down, push on the various components and on the board to see if there are any other intermittent problems.

As a side note, The first thing you do when working on any electronic component is to confirm that all power supply voltages are present and as they should be.