How to fix Noise at first powered on in Primare A30.2 - High DC offset

Hello,

I won a Primare A30.2 in eBay, but there is problem. When I first power it on, there is long noisy (about 30 second 3 months ago, but now about 5 minutes), then the noise stopped. Then, when there is the signal from the preamplifier, it need about 10 second for the right channel to get full power as in the left one.

I take some measurements and found that the DC at the input always very high, about 5V DC.

Please someone help me to fix the problem.

Thanks in advanced!