Help with what could be causing this problem
I a Sansui 8700DB and have this hooked up currently (and have for years) ...works fine at moderate sound levels, cuts out at higher volumes.(Safely Operate light blinks). This happens at about 10-11 o'clock on the 2 inch volume dial. When I power it off and and back on again it fires right up and resumes play.The L channel sometimes drops to a lower volume too.Any thoughts? All suggestions appreciated.
other possibilities.
I would check some easy/simple things first before jumping into the insides of your Sansui. Then after trying the easy/simple things pop the top off & do some troubleshooting.
1) Check ALL your speaker cables & connections for frayed and or shorted wires either to them selves (+ to -) OR either the + or - to ground or the chassis of the Sansui.
Also make sure the connections are good & tight.
2) Have you changed your speakers and or added any speakers to your system? If you have the impedence may be lower even much lower causing the Sansui's protection circuit to trip sooner. Doing what it was designed to do, PROTECT the amp from damage.
3) Check all input/output connections, connectors and cables to verify they are clean & not damaged or broken. These could/might cause a sudden signal spike that would send the amp into protection mode because a sudden over driving of the output stages.
the next one would/could have the same effect as #3 but you will have to open the Sansui to fix it.
4) Dirty/scratchy controls including volume, bass, mid, treble, function switches. Clean as needed with a good product like those made by Caig.
Heat could also be a factor.
5) Over heating caused by poor air flow. Could be caused by something blocking the cooling vents or a build up of dust & dirt inside the Sansui. Give it a good cleaning using forced air (either from a can or compressor) and or vacuum. Must be carefull doing either to prevent damage due to too much pressure.
NOTE: Unit MUST be unpluged from ANY power source.
Hope this and or the other post help.
Electronics Tech.
Old Receivers
Sometimes older transistors lose gain or beta over time, such as when a long tail pair both get weak or suddenly differ in their gain by a large amount. This shows up as failure to properly amplify when you crank up the volume or as a loss of high frequencies. This could also be defective coupling caps or bypass caps, so you need a service manual for your Sansui 8700DB Receiver, a precision sine wave and square wave signal source, a good oscilloscope, test loads, and other test gear (a THD Analyzer) to look for the source of the problem or problems, and you have to understand and know what you are doing and what you are looking for. The alternative would be to shotgun it by replacing all the small signal transistors, and coupling caps, and bypass caps, which after maybe ten or twenty hours of work and considerable cost, that may not solve it completely or it may be the complete answer, hey its old stuff, lots can go wrong...
Hope that helps,
-Steven
Steven L. Bender, Designer of Vintage Audio Equipment