Recap, restore, restomod a SX-580

[dlucy]

I've started prep work for returning a SX-580 to another 30 years of service. I've got some snippets from other threads to use as the basis for the BOM, but I'll update those here with what I find in this unit and what others have mentioned or corrected along the way.

 

[dlucy]

The first thing I noticed was a darkened spot under the Q401 transistor in the power supply. The underside of the PCB seems darker than everything else, so I'm guessing it has gotten too hot too often.



My first thoughts are to figure out why and, if necessary, makes changes so this doesn't happen in the future. First thing was to look at the parts lists in the service manual (since I haven't pulled the transistor out of the circuit yet), but the manual lists more than one transistor:

2SD712-C or D Q401
(2SD313-D or E)​

I can't seem to find a legend to explain the second part number. It this an acceptable substitute? A Part for non-NA units?

Any ideas on why this power supply regulator (?) would get too hot?

 

[dlucy]

The first thing I noticed was a darkened spot under the Q401 transistor in the power supply. The underside of the PCB seems darker than everything else, so I'm guessing it has gotten too hot too often.

Sounds like this is a common issue on the SX-n80 series... http://www.audiokarma.org/forums/in...ns-about-the-transistors.694269/#post-9281824

 

[dlucy]

The 2SD712 is giving me less-than-correct voltages:

E -> 2.94V
C -> 30.28V
B -> 3.64V