Hello,
On a CD drive, after about 30min the audio start to deteriorate and converts from "music" to "noise". This happens whatever the CD is inserted, and it seems to be a "thermal" issue because if we let it cool for an hour, it outputs music again.
When looking inside the CD player, I found a resistor on the audio path that it way too warm and this seems strange to me.
On the schematic above, the GND symbol to the right is connected to the carcass and also to the power supply mains earth. This is thus the 0 potential reference.
The fact that I measure -7.8VDC at the output stage of the preamplifier feels strange.
When looking at the schematic, I had some clues and measured the voltage between the "Audio GND" and the "Carcass GND" and measured -7.8 VDC. This bias is applied to the resistance and thus generates about 1.2W which is way too much for it and make it warm/hot.
I wonder if this is "wanted" and the manufacturer was a lit shy on the resistant power capacity, or this bias is not part of the design and comes from the preamp.
From this schematic, there is a possibility to get a potential of 8V from the power supply of the preamps, but though the 2 resistors of 15k that should not be enough to drive a watt on the burned resistor. C35 may be shorted but sound is available on both channels, so the amp U4 is working.
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