Audio Systems: Pioneer SX-1250 vintage receiver no sound, pioneer sx, bad cap

Question
QUESTION: I recently purchased a 1977 vintage Pioneer SX-1250 receiver.  According to the prior owner it worked fine, had sat dormant in his house for about 5 years without being used.  Now, it powers on and all the lights and tuning meters work but no sound is output.  No sound through the headphone jacks either.  No sound thru the pre out jacks being fed into a known good receiver either.  When it is powered on, no “click” is heard a few seconds later as in most receivers.  I took the bottom cover off and it appears one of the 4 large capacitors had been oozing and leaking fluid down onto the bottom pan (no fresh wetness at this point).  Could one bad capacitor cause this or could it be something else?  Could a bad capacitor cause the protection circuit to mute the unit?  I have purchased a OEM service manual (which references the protection circuit) but it is of little help for a neophyte like myself other than for parts ID.  I would like to fix the unit myself if possible but the hard part is determining the cause of the failure.   I bought this receiver as a hobby unit because I like the old ones, so it’s not a question of repair vs. replace, I know I want to repair it.   I know the new ones are cheaper and technically have better specs but I like the look, feel, and sound of the vintage ones.  Thank you.

ANSWER: OK.  A few things:
1) I don't recall whether or not the 1250 had a speaker relay, I don't think so, so a click won't be heard.  Look for speaker fuses.  These should be on the back of the unit.  
2) The fact that there is no sound present at the pre-amp outputs suggests a front-end problem.  Get some electronics switch cleaner and spray all of the switches and controls.  Work them back and forth a number of times after spraying and try the unit again.  With a unit this old, dirt and debris can collect on the controls and prevent contact.
3) A bad cap in the power supply is not the likely cause of this.
4) The protection circuit does not effect the pre-amp out, only the final amp stage.

All this being said, tracing this down will not be easy remotely.  This is definately a unit worth saving.  Expect a repair cost of $25 or so for parts plus the local labor rate.

Dan

---------- FOLLOW-UP ----------

QUESTION: Thanks for the response Dan.  I tried it again with the pre outs and contrary to what I thought originally, they do work. I get tuner output and aux (CD player) output.  all the tone controls, volume etc affect the sound thru the pre outs and appear to function (though some scratchy).  There are no speaker fuses on the unit and I beleive per the manual it has relays.  It has a protection circuit which is composed of a relay driver circuit, overload detector circuit, and center point detector circuit. The protection circuit protects transistors in case of overload, speakers in case of power amp malfunction.  It states the relay circuit performs muting function when turning on and off as well as shutting off signal.  So it appears there is a malfunction somewhere which is preventing the relay swtich from opening the signal to the speakers and phones?  Any suggestions for testing to deterimine what?  The manual has no troubleshooting guide, etc.
thanks
Chris

Answer
With output at the pre-amp jacks, the front end is good.  Cleaning all of the controls will eliminate the scratchy sound.  The amp section has a problem.  It can be anything from shorted output transistors to a noisy dif-amp section.  Without taking measurements, it will be hard for me to determine the exact problem.  Perhaps the most common is the shorted outputs.  Remove the output transistors completely and you should be able to measure the DC voltage on each of the three legs.  It should be (0.0V, +/-0.6V and B+/B-) If these are present, the outputs are bad and should be replaced.  If the voltages are not as listed, go back a stage and check the transistors there...
Dan