Rotel RCD-951: Distorted sound on one channel

On the workbench I got a nice Rotel CD player with an error in the analog output. Digital output was working fine. The right channel sounded distorted.

First let’s put in an ordinary CD and listen to the sound and view both signals on the two channels off the scope.

The blue wave form looks like an audio signal, but the yellow signal definitely does not.

Let’s see what a 1kHz signal looks like:

That is not what it should look like. Is it the DAC that is missing some bits or is it the digital signal that is feed into the DAC.

I grabbed my USB datalogger and connected a few clips to the digital input of the DAC.

How does the left and right channel look like when an 1kHz signal is played.

Digital signal of 1kHz mono

Left and right are digitally not identical because it still is a two channel recording. But the data in both the left and right channel look the same. It’s not like there are bits missing.

New DAC

The DAC in this player, is a BurrBrown PCM69AP. I ordered a new one and soldered it in.

Fixed 1kHz signal

And it’s working again!

Output stage

Another view on the DAC with the output stage. High quality Rubycon Black Gate capacitors.

Final test and ready to go back to the owner.

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