Sansui AU-5900 Preamp Hiss noise and abnormal voltage

[ALVintage passion]

Hi everyone

I restored recently my AU-5900 that is replacing electrolytic caps, replacing small signal transistors and diodes , fuse resistors etc. I’ve done it in the past on the same model for few friends with success.

On the power amp side, result was ok will all voltage levels good and bias set up right.

However during testing I noticed that the quality of sound had degraded and specially got a background HISS noise on the speakers even if the volume is at minimum.

I further investigated and confirmed the noise being from the preamp.

I also noticed the following:

1. On F2604, the collector voltage of both TR03 and 04 was 6.7V in lieu of 9.2V as written in the service Manual. All other voltages on the transistors seem ok. Note on preamp I used KSC1845FTA and Nichicon KZ , ELNA silmics

2. On F2599, the voltage readings are somewhat lower at the outputs: 20.7V and -27.6V in lieu of 22V and -29V.
Please see in attached photo complete voltage measurements on the preamp voltage regulator.

For components on this regulator :

1. A726 and C1313 was replaced with KSA992 and KSC1845
2. E Capacitors was replaced with Nichicon KZ and FW type
3. Zener diode RD-13EB was replaced with 1N4743A
4. B526 and D386 replaced with A940 and C2073

All resistors checked ok

Could you please assist as I am really stuck with this since over a week.

I do not understand as I have checked again everything

Thanks and regards

AL