Some receivers present serious issues I am unable to remedy.  These unfortunately  can not be sold as working units. 

2 examples are pictured above (Sansui G-4700 on top, Hitachi SR-804 on the bottom).  

The Sansui was blowing fuses and the Hitachi would not come out of protection.  This is typically due to shorted output transistors on one or both channels.  

Many times, shorted outputs are due to user mistakes like accidentally shorted speaker wires.  For these, installing fresh parts to replaced damaged ones is all that is required to restore reliable operation. 

Then there are cases where the amplifier has a fundamental issue that caused the devices to overload/fail.  These can be tricky to completely debug.  The Sansui G-4700 and Hitachi SR-804 fell into this latter category.

Sansui G-4700 

I got this receiver fairly cheap as it was blowing fuses.  It does not use a protection relay and instead relies on fuses/fuse resistors to somewhat protect the amplifier and speakers.  As expected, I found one channel had 2 shorted output transistors, so I replaced these on both channels for matched left/right performance.  I also checked the “up stream” transistors from the shorted devices and replaced any of those that were also damaged/suspect.  The amplifier than powered up correctly and a full recap was performed. 

Final amplifier testing with 8 ohm loads showed an alarming collapse of one channel at ~10 watts (distorting far short of the 50 watt spec met on the other channel).  Particularly alarming was a large increase in DC voltage on the failing channel into “speaker killing” ranges.

I spent weeks comparing the good vs bad channels, swapping parts and getting ideas on AudioKarma.  In the end I had to give up and eat the money had had invested in this receiver as I could not in good conscious sell this as a working unit.

Hitachi SR-804

This features an unusual Class G amplifier that would not come out of protection.  I found several fuse resistors that had been over stressed by high currents and had resistances way out of spec including one that was totally open.  Replacing these enabled correct amplifier power-up and release of protect mode.  Recap completed, but sustained testing showed the Right channel power meters twitching and then jumping to alarming levels despite volume being set to min.  This “insane” behavior was intermittent and could disappear for days before returning with a vengeance. This made debug and resolution testing quite time consuming. 

I again spent weeks trying to resolve this by swapping devices between channels, replacing the main amp board edge connectors and consulting with others on AudioKarma that saw the same frustrating issue on their SR-804 projects.  I again had to throw in the towel and never sell this otherwise fully functional receiver.

Next step

I decided to sell both of these very cheaply to a local customer who I saw parting out other vintage receivers.  These were transferred with the firm understanding that they would only be parted-out (except the amplifier sections which are junk).  As I have benefited from others selling vintage parted-out components I desperately needed, I thought this was the best option for these otherwise unsellable receivers.