As Batkosio said your DSP is most likely burned because somebody played a tape on it

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The bad news

- Most of the times the most loaded DSP channel burns because of the high heat which is one transistor circuit + one diode which prevents the chipset & amplifier to get the peak voltage back, however sometimes the voltaage jumps above the diode and it burns the chipset.I have dealt with two like this plus one legend's double din so far and fixed them both.
The good news

- It si easy to diagnose and repair if you understand or have an idea about electronics, electronic devices and low power curcuits. From the sympthoms that you describe your DSP is easy repairable.
If you have any additional questions PM me, I will be more than glad to help you out
