- Electrolytics filtering VCC (C685) and CREF (C642) replaced.
- Crackling / popping (C/P) is on the Line Out RCA jacks as well as the speakers.
- C/P corresponds to significant spikes on the analog supplies; digital supplies seem OK.
- C/P on any input selection mode
Is C686 (470uF) the capacitor you replaced on the VCC power supply rail (pin 2 of TDA7313)?
If crackling/popping still persists after everything is totally clean and dry, then IC TDA7313
might be faulty.
Also, if there was lots of contamination/dirt near the TDA7313, then there could still be residual contamination underneath the IC chip. At times I desoldered an IC chip in order to get the PC board underneath sufficiently clean. In the case of desoldering the TDA7313 for this purpose it would be a good idea to obtain a replacement TDA7313 IC just in case the original IC has actually failed. Note: I use "chipquick" low-temperature alloy when desoldering parts like the TDA7313. I've found Bose PC boards to be somewhat delicate: their foils are narrow and the pads are small. I don't want to damage the PC board when I replace components. Chipquick desoldering alloy works very well for this. Only a small amount is needed. Spread some rosin flux on the IC pins, then melt a bit of the chipquick onto each IC pin with a soldering iron. Then a heat gun or hot-air rework gun will melt the chipquick alloy very quickly. The IC chip will lift right off leaving the PC board in perfect condition. Then use desoldering wick to remove all vestiges of old solder and chipquick before reassembly.
The TDA7313 operates entirely on a single positive rail voltage filtered by C686 and input into pin 2. The IC contains an internal regulator filtered by C642. The DC voltage at pin 1 (CREF) should be approximately 1/2 of the DC voltage at pin 2. The TDA7313 does
not use a negative rail supply.
I recommend re-checking the polarity of the replaced capacitors C686 and C642
Also please measure the DC voltages at TDA7313 pins 1 and 2 and post them. According to datasheet the ideal supply voltage for the TDA7313 at pin 2 is 9.0V
I attached TDA7313 datasheet.