Pioneer SX-636 Receiver Repairs (Ep. 64)

Gawd awful noise when powered up. This repair is for a local customer. Let's see what we can do for this.

[@craigm.9070]

Great job! Another mid-70's music maker granted a longer life! I enjoy watching experienced, long-time tech's think out loud with decades of experience; in this case it was the blue Sanyo cap's that had kind of turned into resistors. Even with the Grey cap leakage that was enough to corrode one contact leg off, I did not see board damage. I know the customer will be happy to get his receiver back in working condition.

[@garystonley9004]

Thank you! I was changing out the lights in my SX-636 and replacing a couple of capacitors while diagnosing a lot of noise and this was a help to me. I ended up replacing the same three caps plus a couple of others and she now sounds great!

[@TrevorsBench]

Glad to hear the video was helpful

[@VintageAudioFever]

Man!!! nice job on this Pioneer....well done!

[@zulumax1]

I was measuring the ESR with my MESR-100 meter measuring across the leads on the component side because the test leads they give you on that meter are alligator clips with rubber booties. The Sanyo 0.33/25 volt caps measured 19 ohms, and yes the cap was shorted prior to hooking up the leads. However the alligator clip popped off of the negative lead and bumped between the base and the collector metal can of the bias transistor Q5. There was quite a charge on that -41 volt power supply, because it was not plugged in. There was a pop as those 220 uF capacitors discharged across the 2SA777 and shorted it collector/emitter. I did bring it up on a 60 watt dim bulb after the incident, and it lit up bright. I substituted KSA1013YTA and complement pair device KSC2383YTA in lieu of the 2SA777 and 2SC1509. The subs ran an extra 100 hFe hotter than the stock transistors, now the bias will only come down to 28mV with the bias trimmer set all the way to minimum. Stock bias is 20mV, but the service manual did not say plus or minus figure. Nothing runs hot, but I don't like the idea of having a hot bias and not being able to turn it down. Any ideas?

[@PioneerGuy581]

nice easy video to understand.

[@thelifeemery]

I have the same unit and I am getting random static and pops even when the unit is powered off. I suspect the same three caps but unsure.

[@TrevorsBench]

Hi David, It shouldn't be making noises when powered off. I suspect cracked solders in the power amplifier or failing transistors. It would need to be diagnosed on a bench to be sure.

[@kdlc56]

How much to just change lamp ?

[@zulumax1]

Which transistors did you sub for the drivers on this unit? Look like all TO-220 devices.

[@Bulltardwin]

It's it possible to play a tablet/ phone through this?

[@TrevorsBench]

Yes but you'll need a stereo 3.5mm plug to RCA adapter cable

[@Bulltardwin]

@@TrevorsBench thanks for the reply. Are these generally good quality? I've found one second hand which I'd love to get as my first vintage receiver

[@TrevorsBench]

@@Bulltardwin Depends, at this age it's anybody's guess how it's held up. Aside from burnt out lamps, capacitors are the next biggest problem you may encounter. Even with weak or failing caps the receiver may work and sound good. Sorry, I can't advise you any better on this, every receiver is different Have a listen if possible and see if it sounds pleasing to you.

[@Bulltardwin]

@@TrevorsBench ok thanks mate