Sansui 551 Repair

[callensky1]

Found a 551 for $10 at a yard sale. Only the right channel works (both A and B). Tested caps and resistors, replaced blown fuses, replaced all 4 transistors - still no L channel audio. Checked voltage, checked capacitance, etc. and all checks out. What could I be missing?

 

[PF Sound]

Is it the same for all inputs & am/fm? Where did you "check" voltages? Did you deox all the switches/controls?

 

[skippy124]

If you haven’t cleaned any of the switches, then do that (particularly the source switch) and see if that helps

 

[callensky1]

Deox'd/cleaned everything I can think of. I did replace a few resistors/caps that were weak. Checked voltage along the way. Most everything running +/- 55v. I am confused, however, with the voltage setting L to R. Schematic shows 56v for one side, half that for the other. Shouldn't the voltage bias be equal for both sides?

 

[skippy124]

Hi,

Not entirely sure what you mean by the voltages that you have described.

This is a capacitor coupled output power amp design, and as such it has a single rail supply. in this particular receiver the supply is +52V nominal. and other voltages used elsewhere in the unit are derived from this supply. There is a voltage of 26V shown on the schematic at the amplifier side ( + ) of the output coupling caps C43 (left channel) and C44 (right channel).

Can you advise what 4 transisters were replaced and what part number replacements were used?