The problem is caused by a faulty 7915（the measured voltage is -21V instead of -15V) and after replacing the

regulator, a dead 9000 comes to live but the output audio signals accompany with unexpected loud annoying cracking distortion sound

properly a symptom of burn fets(Tr102 and Tr202) as the outputs are taken from R156 and R256.

The burnt PF5103 fets are difficult to get.

And  now I needed to tackle the problems of audio dB level display.It seems that the level display is in working order but

with normal audio signal input ,the display hardly shown above -20dB! When cracking distortion sound get in,the level meter would shoot

to full scale to +5dB.

And you can`t find any information given in regarding to the calibration of audio display meter.