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Pioneer SX-650 doesn't power on

thenewguy

thenewguy

Active Member
Hi everyone. Just picked up my first piece of vintage Pioneer gear, the SX-650. Immaculate condition, I was so excited! Got it home and set up for a trial run. Nothing. :sigh: So I pulled the cover, very clean inside, and DeOxed the pots. Tried again and this time I could see the the dial lamps would flicker and I heard a sound like, well, something frying in a miniature frying pan. The sound is coming from the front near the power/speaker switch, maybe from the 2 little blue cans (capacitors?) right next to the switch. Did I make things worse by turning it on? Can you tell that I'm new at this? What I'm wondering is if it's worth trying to fix this beautiful piece of equipment? I think I'm capable of the de-solder/solder part of the repair, if the blue caps are the problem, but identifying and tracing circuits is way beyond me. Is it likely more and greater things are wrong with this piece? Is the SX-650 prone to this kind of failure? I've only got $3.00 invested in this :) so I'm prepared to dig a bit deeper in order to repair it. Also, what a great forum this is. Thanks to all!!
 
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Its the power switch, it is burned and has a high resistance.

It can be removed if you are confident in your mechanical skills, and it can be opened and the contacts burnished, then reassembled.

There are 2 threads in here that discuss the problem.

similar symptoms

this has a picture

attachment.php
 
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markthefixer said:
Its the power switch, it is burned and has a high resistance.

It can be removed if you are confident in your mechanical skills, and it can be opened and the contacts burnished, then reassembled.

There are 2 threads in here that discuss the problem.
Click to expand...

If it is the switch (common problem with vintage) there is also another option. You can solder a jumper across the two switch contacts, causing the power to alwaybe on. You then can use an external switching AC strip to power the unit on and off. I would first see if you can inspect and clean/burnish the switch contacts and if not jumper it out.

Lefty
 
That sure sounds like the solution. Mechanical problems I can handle. The switch has a label on it and appears to be a Noble E-35961. I'll go for the burnish idea first, as suggested. I've got tomorrow off work and the weather up here in Maine is awful right now, so it will be a great indoor job. I'll post back when I get it going. Thanks for heading me in the right direction!
 
What a great way to spend a day off in the middle of the week. Good luck with her, you might want to check.reseat any fuses whule you're in there. Welcome to the fun. :banana2:
 
Well, I almost had a day off. My father-in-law called at 8:30 this morning asking if I would help him change out a water heater in one of his rental houses, didn't get back home 'till 2:00 in the afternoon, whereupon I commenced disassembling the SX-650. I bet there were at least 25 screws that had to come out in order to reach the switch. Not to mention the string that runs the tuning indicator needle. I ended up cutting the two wires that connect to the power part of the switch. The Noble E-35961 switch looks nothing like the one in the picture above and is riveted together, so I ground off the peened end of the rivets and punched them out to get the thing apart. Definetly burned contacts, reminded me of the points in my '65
Falcon years ago. Ended up using my spiffy binocular dissecting microscope and a scalpel to carve a new contact surface on the post, which is made of some brass alloy on a copper core, fine sandpaper on the disc contact. Kept at it untill I consistantly got 0 ohms on the meter when I flipped it. Also took out the little clothspin type spring and tweeked it back the other way so it would push harder on the arm. Pretty good design overall, just weak on contact materials. I found a couple of miniature nuts and bolts, drilled the rivet holes in the switch body and back plate out a couple of sizes and the whole thing was back to good as new. I don't think the switch will last all that long, couple years maybe, so I soldered pigtails on the terminals and soldered them to the power wires. That way it won't be such a huge pain to jumper the switch if it doesn't work, or if it does, when it fails next time. :thmbsp: So far I've got about 5 hours into it. DeOx'ed all the other switches again, seein' as how it was all opened up. Put everthing back together. Only lost one screw, not bad. Hooked up an Magnavox FD-2040 SL12 CD player, tied on a pair of Akai SW-137II's and turned the switch. :banana2: Yippee! Not bad, eh? Listening to Cesars Palace. Man, this thing really cranks, the Akais can't take it, there only 40 watts. What's the output on the 650 anyway? I'm very pleased. :yes:
 
Congratulations on a nasty job well done....
That IS an ACCOMPLISHMENT....

Specifications:

Power Output: 35 watts per channel RMS into 8 ohms.
Harmonic Distortion: Less than 0.3%
Intermodulation Distortion: Less than 0.3%

FM Sensitivity: 1.9uV
FM Capture Ratio: 1.00
FM Harmonic Distortion Mono: <0.15%
FM Harmonic Distortion Stereo: <0.3%


Dimensions: 19 x 6 x 14.5
Weight: 29.00 lbs

compliments of classicaudio.com

Running it off of a power strip will preserve the switches life, as the damage is usually from arcing and burning, not heat generated by contact resistance.

Without getting into power rating discussions, this rating was established under the old FTC rating system, where it had to be delivering the rated power continuously for a considerable fraction of an hour. No numbers games here.. Those older Pioneers can really sing.. as many have re-discovered.


P.s. I had a water heater from hell replacement job in my basement a while back... the only good thing I did when I got the house and redid the plumbing years ago was to put ball valves on both hot and cold lines feeding it, now flexy hard lines feed the water and the gas... and I had to completely re-do the flue from it to the chimney, including sealing the new flue to the brick chimney... fun...
 
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Thanks for the specs! The Akais should take everything the receiver puts out, but I didn't even make it to half volume and it sounded like they were about to blow. Things got a little better after I adjusted the crossovers and turned the loudness lever off :rolleyes: I'll mess around with it some more tomorrow, try the tuner, hook up a TT and so on. Very cool looking piece of equipment.
 
The only thing that I have ever wished those Pioneers had is a set of clipping indicators, to wink at me when I was asking too much of it...
Then I would really know I wasn't getting more volume, just distortion.
 
Nice work on that switch. Grinding off the rivet & hardware to put back together. Not intimidated with overcoming obstacles. You'll be fine around here.

The power switch problem is common with those fellows. Loudness 'on' will cause the unit to clip sooner (exceed power supply capacity). That can likely be improved with better main filter caps.

Be aware that these units also have problems with fractured solder joints for the output drivers, main power supply caps, and speaker terminals. I suspect that, if you will examine the main supply cap joints, you will see evidence of arcing. THAT is what took out your switch, if so (and what is limiting your output capacity).

Just take a 10x loupe and carefully examine the solder joints in those areas especially and all around the bottom of the main board.

Enjoy...

Rich P
 
DOH Missed that... :withstpd:

Rich P as usual is spot on.....

pustelniakr said:
I suspect that, if you will examine the main supply cap joints, you will see evidence of arcing. THAT is what took out your switch, if so (and what is limiting your output capacity).
Rich P
Click to expand...
 
markthefixer said:
The only thing that I have ever wished those Pioneers had is a set of clipping indicators, to wink at me when I was asking too much of it...
Then I would really know I wasn't getting more volume, just distortion.
Click to expand...

You would really like the SA-7700. It has nice overload indicators (clipping). Now, I could design a nice circuit that would change the color of the power indicator. I kind of like that idea. I think I'll do that on one of my 'sweetening projects'. Right now, I'm working on a design for a solid-state, bi-polar fuse lamp replacement, using white LEDs. It would be a drop in replacement for the incandescent ones that are so hard to find lately, and they won't ever burn out (as an extra added bonus). They will be significantly more expensive though.

Thanks for the idea Mark :) Imagine the standard Pioneer amber power indicator, that turns red if either channel clips...

Rich P
 
pustelniakr said:
Be aware that these units also have problems with fractured solder joints for the output drivers, main power supply caps, and speaker terminals. I suspect that, if you will examine the main supply cap joints, you will see evidence of arcing. THAT is what took out your switch, if so (and what is limiting your output capacity).

Just take a 10x loupe and carefully examine the solder joints in those areas especially and all around the bottom of the main board.

Enjoy...

Rich P
Click to expand...


Thanks for the tip. I'll flip it over tonight and take a look inside.
 
pustelniakr said:
You would really like the SA-7700. It has nice overload indicators (clipping). Now, I could design a nice circuit that would change the color of the power indicator. I kind of like that idea. I think I'll do that on one of my 'sweetening projects'. Right now, I'm working on a design for a solid-state, bi-polar fuse lamp replacement, using white LEDs. It would be a drop in replacement for the incandescent ones that are so hard to find lately, and they won't ever burn out (as an extra added bonus). They will be significantly more expensive though.

Thanks for the idea Mark :) Imagine the standard Pioneer amber power indicator, that turns red if either channel clips...

Rich P
Click to expand...

I was pondering those very subjects last night in the dark, for my sx-636, i.e. how to show clipping without physically changing the front panel!!!!
I've no power indicator there, but was looking at that dial pointer with evil intent!!!!! Imagine it (sorta amber) flashing brilliant RED when clipping!!!!
Now I imagine the entire face changing color when it clips!!! muuuhahahah!!!!!
(halloween must be catching, as well as this sox thing, whole city went happy nuts..)

P.s. I have been collecting clipping circuits, do you have electronic versions of the 7700's? (I'm gonna funnel 4 clip inputs into one output.)
 
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pustelniakr said:
Thanks for the idea Mark :) Imagine the standard Pioneer amber power indicator, that turns red if either channel clips...

Rich P
Click to expand...

Fascinating possibility Rich! Are you imagining a fairly generic circuit that could be applied in a variety of amps... or would this typically need to be purpose built?

..many questions come to mind....

1) How costly would this be?

2) Would there be any downside in terms of altering the behaviour of the amp?

3) How are you proposing to measure "clipping", or are you just thinking of triggering the LEZD based on a specific level of peak power output?
 
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hpsenicka said:
Fascinating possibility Rich! Are you imagining a fairly generic circuit that could be applied in a variety of amps... or would this typically need to be purpose built?

..many questions come to mind....

1) How costly would this be?

2) Would there be any downside in terms of altering the behaviour of the amp?

3) How are you proposing to measure "clipping", or are you just thinking of triggering the LEZD based on a specific level of peak power output?
Click to expand...

I'm not sure yet what I would monitor. I could compare the output voltages to the power supply rails, and if the output levels draw to within a threshold of the rails, that could trigger the lamp color change (or other indication). Bi-color LEDs would replace the standard incandescent lamps where implemented.

I'll look at how the Pioneer guys sensed overload/clipping on the SA-7700. This kind of thing is a heck of a lot simpler for me, than trying to reverse-engineer 30 year old designs :)

There are many ways this could manifest, on a model by model basis. Meter lamps changing color. Red dial highlighting, power lamp changes, etc. Specific designs first, followed by attempts at making generic applications.

Normally, I'm not one to make mods, but this one may be non-invasive enough not to scare me off...

Rich P
 
The clipping circuits I have seen take the +/- of the final output supplies (the actual clipping point?) and look at the output voltages, and if they come within.. say.. about a diode drop (or transistor conductivity bias) to either supply rail they trigger, so there is a + and a - "monitor" each, for each channel thus the 4 into one reference...
No adjustment necessary, but they have their own led.....
I was looking for the schematic last night, and today, but it has dissapeared itself in the bowels of my hard drive... or I would discuss it further (and post it).

edit:
found it

this guy came up with a pc board for it
 
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So far, so good! Been running the tuner for a couple of hours with no issues. Lamp in the Stereo indicator does not light even though the receiver is functioning in stereo. Haven't got into the underside of it yet to look for cracked or weak solder joints. That's going to be my evening project :)
 
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