Pioneer VSX-D503S Pro-Logic Receiver (Distortion)

[slydogsrus]

I have this Pioneer VSX-D503S Pro Logic Receiver that came in with the typical intermittent audio cutting in and out with static due to the overheated solder connections on the amplifier board.

I got the amplifier board rebuilt and everything works great except I noticed when doing final test of the unit in any "surround sound" mode the "right" front channel has severe distortion but only the right front channel, the left, rear, and center channels are clear as a bell.

If "surround" mode is off the right channel sounds great. I have checked for solder bridges on the DSP pro logic board, and tested input and output caps, along with even tapping the signal straight from the output of the DSP board "L OUT" and "R OUT" and all sounds great in stereo or surround mode.

I realize I must be missing something here and have never ran into this problem before with only one of the front channels having such severe distortion but only when surround mode is on, almost like a bad cap or op amp.

Any help or tips where to check next would be appreciated, as would the schematic as I am working without one currently to save costs on the repair.

Thanks, Slydogsrus

 

[slydogsrus]

Today I applied a 1khz sine wave with a tone generator and determined the fault is in the DSP Pro Logic board.

The level on the "right" channel drops by 50% and starts clipping with surround mode on and the " left" channel changes amplitude some with surround on but has no clipping at all. Both the "right" and "left" channels sound great and have equal amplitude when bypassing the DSP board and just running stereo mode.

Now I really need a schematic for the Pioneer VSX-D503S as I am unable to even find a pinout for the Sanyo LA2785 IC that controls surround modes. Board number is ANP1763-B, which also seems to be a rare part number.

Thanks, Slydogsrus