Pioneer KEX-M900 troubleshooting

[Perry Babin]

Pin 5 shouldn't drag the signal down. The IC or one of the capacitors connected to pin 5 may be defective.

 

[vincegironda]

Thanks Perry

Sorry I'm a little confused, by IC do you mean IC757?

There are 4 capacitors in the 763 circuit should I go ahead and replace all 4?

 

[vincegironda]

I just pulled the caps and tested them, all appear good and within tolerance

 

[Perry Babin]

I was referring to the op-amp IC763 (the one that caused the signal from IC764 to be dragged down).

Before replacing anything, measure the resistance from IC763, pin 5 to ground and compare that resistance to the readings on pin 5 of the other op-amps.

 

[vincegironda]

Pin 5 to ground resistance

764 42.8 k Ohm
763 000.7 Ohm
762 43.1 k Ohm
761 1.93 m Ohm

 

[Perry Babin]

If it's easily accessible, remove it and re-check.

 

[vincegironda]

With 763 removed

764 42.8 k Ohm
763 000.2 ohm
762 43.1 k Ohm
761 1.8 m Ohm

 

[Perry Babin]

It would appear that the fault is a shorted capacitor.

 

[vincegironda]

I just checked all the capacitors on the dsp board and none are shorted

Should I pull them off the board and re test?

 

[Perry Babin]

Something connected to pin 5 has to be shorted. C793 is the most likely suspect.

 

[vincegironda]

C793 is an Smd capacitor, not sure how to check it for a short

 

[vincegironda]

I pulled C793, 787, 801, 814, 813, 797 and 805 all test good and pin 5 is still grounding to earth?

 

[Perry Babin]

I don't see anything else that could go to ground. Maybe R789, in parallel with C793?

 

[vincegironda]

Thanks again Perry but no luck with R789 either
Back to the schematic to see if I've missed anything