SU-9070 help ??

[bobrown14]

Hi folks I'm new here. I have a question about the SU-9070 preamp. First off I have one channel with no output. I'd like to troubleshoot but don't know where to test the unit as I do not have the service manual. Can any one help me out with this? Please?

Thanks,

Bob Brown

[anatech]

Hi Bob,
What kind of experience do you have?
What test equipment do you have?

I've repaired many things without a manual, only because I've repaired many with a manual.

-Chris

[ma_coule]

Originally posted by bobrown14
First off I have one channel with no output.

The same happened to me! As I remember it were input/output selectors (bad contact). Try to measure (or change) them.
I have original manuals for Technics SU-9070. If you need them I can send you a copy (please, post your e-mail).
Regards,

[bobrown14]

Ok I fixed the outputs and all was well then I left the preamp on overnight and then in the morning the preamps relay started shutting the unit off and on. I've ordered a full set of caps and will replace them all. I've been looking at the transitors and there are a few I can't find. Specifically the differential Amplifier transitors, SVTM57L, SVT47L and the SVIUPA63H1. I will recap the unit then see how that goes but does anyone know what I should do (if anything) with the differential amplifier parts I can't locate?

The reason for thinking of replacing the transistors is due to the heat these babies give off. My board is discolored where the transistors are from the heat and I can feel them getting hot even when the cover is off. This unit may have spent a bunch of it's life couped up in a with little ventilation hence the heat issues. A few caps show signs of age and for sure should be replaced but do I need to worry about the transistors as well?

Thanks in advance,

Bob Brown

[anatech]

Hi Bob,
Wait until your caps are replaced and test again. The solder connections on these may need to be redone. Do remove the old solder first and avoid solder blobs.

-Chris