I took a look at the service manual, at hifiengine.com. It appears that they are somewhat arbitrarily defining 0 dB as corresponding to a voltage of 500 mv, with other voltages that are expressed in dB undoubtedly being related to that 500 mv level in accordance with the standard formula for expressing the ratio of two voltages in dB:

dB = 20 x log(V1/V2)

where "log" is the base-10 logarithm.

So for example the reference in the procedure to a voltage level of -20 dB would correspond to a voltage of 50 mv, since:

20 x log(50/500) = -20 db

And the reference you stated to 500 mv -2 dB would mean 2 dB less than 500 mv, which I calculate to be 397.1 mv:

20 x log(397.1/500) = -2.00 db

Hope that helps. Regards,

-- Al

dB = 20 x log(V1/V2)

where "log" is the base-10 logarithm.

So for example the reference in the procedure to a voltage level of -20 dB would correspond to a voltage of 50 mv, since:

20 x log(50/500) = -20 db

And the reference you stated to 500 mv -2 dB would mean 2 dB less than 500 mv, which I calculate to be 397.1 mv:

20 x log(397.1/500) = -2.00 db

Hope that helps. Regards,

-- Al