I have a Pioneer VSX-40 that I am trying to repair. It would not turn on initially. I found the right front channel blown, replaced both transistors and 4 resistors. Now it will power on fine but there is no audio. I am hoping this isn't the DSP fault that happens on other units. I saw a repair video by someone else with a very similar model & fault and he replaced the audio IC. The schematics seem to be for combined models and are found under the VSX-821-K model. I was just wondering if there is a way to test the audio IC & if it needs to be in circuit to be tested? There's isn't much room to access the IC in place. Currently I have the board removed to access the IC.

 

testing any electronic component requires suitable circuit.
for some of simplest components, like R, C, Diode or BJT those test circuits may be built into a DMM.

 

Hi,
Can you compare the duff channel with the good channel, regarding volt measurements, resistance comparisons, waveforms if you have a 'scope?
Good luck............

 

Now it will power on fine but there is no audio.

Is that no audio from both channels?

 

If there is a fault with one channel, both outputs will be disabled. The protection circuit will sever both speakers.

-Dan

 

Check the voltages for Q419 which is the protection trigger transistor. See page 16 of the service manual for the block diagram and you will see that the protection will mute all channels. Perhaps there is still an issue with the "repaired" channel...

Q405 is the overload detect transistor common to all channels(on the amp assembly). Check there as well.

Perhaps you can list what was blown and replaced so we can suggest other parts that may also be defective.