Pioneer SX-828 help needed

babcoccl

Member
Hello All,

First time poster, long time lurker. I recently bought a Pioneer SX-828 for $100 from a lady moving out of her home. She didn't know anything about it as it was her husbands and it was working "good" right up till she packed it for moving a week earlier. It was packed in the original box and had all the original documents included including the wiring diagram and cleaning cloth. I picked it up and didn't make her prove it to me or anything like that as it was clearly not her gig.

View media item 16418
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Anyway, I got it home, hooked it up and powered it on. Lamps were flickering and would completely dim out after about a minute. Toggling the brightness button on and off would restore the lights but they would gradually dim after a minute to the point where the unit appeared to be off.

This is where I should have stopped but I'm a noob.

I turned the FM mode on. I could barely hear the radio station out of the Horn of my Realistic Mach One.
Once again, should have stopped here.

I flipped the Loudness lever to on. No more sound, no more lamps on even with toggling the dimmer button.

Here's what the current power sequence sounds/looks like:

1. Power on Speaker A.
2. Red STEREO lamp briefly Illuminates
3. Audible "Click", Red lamp shuts off.
4. No more functionality.
I did check the outer fuse is fine and "seated".

I opened the unit up and gave it a vacuum and took off the cover and bottom plate.

I went to the power supply board and measured the voltages on the pins as described in the wiring diagram. Here they are

Pin 2 - Actual 12.1V, Expected 12.0V
Pin 4 - Actual 4.1V, Expected 4.5V
Pin 5 - Actual 31.6V, Expected 32V
Pin 6 - Actual 31.4V, Expected 31V
Pin 7 - Actual 35.6V, Expected 35V
Pin 14 - Actual 43.5V, Expected 44V
Pin 15 - Actual -43.5, Expected -44V

None of these values seem terribly out of line to me but I'd be interested to hear other opinions.

While inside I checked connectivity of all the internal fuses and they were all ok. The one thing I did notice was one of the diodes on the board (right near the center) had 'grown' two very fine hairs, that when the unit was upside down were standing straight up, but I imagine this is a cracked diode? Could this be a problem? I have included pictures and you can see one of the hairs as a very fine black line over some white wire insulation.
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Anyway, my question for the experts, where should I troubleshoot next? My background is in computer engineering and I'm pretty handy with the soldering iron and diagnostic tools so you can talk techie to me. :)

Thanks in advance!
 
Voltages look okay, V on the big ecaps too.
pre-amp out/power amp in jumpers installed
read the owners/service manual
I can not see the fine hairs in your pics
Do you have a proper FM antenna, min a dipole or rabbit ears etc
 
1160984-473bb2aa192c701c5cbf0baf6cbb3e06.jpg
View media item 16414Above should be the link to the picture with the cracked diode, if not it's in my only album on my member profile, you can just make out the 'hair' as a black line in front of the white cloth insulation.

I will continue testing voltages to the pre-amp and amp but probably not until tomorrow.

Yup, have a dipole antenna for FM.
 
My first bit of troubleshooting would be the power switch. IIRC it is tied in with the speaker selections. Jump it from inside and see if the power issue is corrected.
Build a dim-bulb tester before going further for piece of mind and safety.

The power switch is a common issue and once at the switch a easy fix.

Clean all the controls with a zero residue plastic safe cleaner.
 
Regarding general condition, it is a little dusty, but I've seen far worse.

KR-6050Opened.jpg



That can be cleaned up:

KR-6050OpenTop.jpg




I'm not seeing a cracked diode, just the parting lines from the mold.

I would second the motion to jumper the power switch, but it can be done more easily by interconnecting the switched and unswitched receptacles on the rear of the unit using a "cheater" cord.

WARNING! If using a cheater/jumper cord, be absolutely positive regarding polarity of the plugs.

If this is a multi-voltage unit, it would also be reasonable to check the condition of the voltage selector plug.
 
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I got one of these recently and it was stated a missing a channel and probably not working very well.

Deoxit is all it took to make it right. But then I didn't get the box and paperwork. It did not have lighting issues, fortunately.
 
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My first bit of troubleshooting would be the power switch. IIRC it is tied in with the speaker selections. Jump it from inside and see if the power issue is corrected.
Build a dim-bulb tester before going further for piece of mind and safety.

The power switch is a common issue and once at the switch a easy fix.

Clean all the controls with a zero residue plastic safe cleaner.
Lamps were flickering and would completely dim out after about a minute.

Concur..
 
Ok, so I will start this post out with, "I'm dumb" and "I didn't RTFM".

Came across this while wondering WTF the volume was so quiet, I did get the volume to restore after correctly tuning to a powerful station.

So in desperation, I decided to read the manual and found this:

IMG_20180925_130459.jpg
Awww, srsly? Quietness problem solved.

Now onto the dimming issue, I sprayed some contact cleaner in there and worked the switch constantly for 3-5 minutes in and out. When I turned the unit back on the lights came back on full bore, then died out after about a minute. Nuts. I found that by holding the dimmer button in about halfway the light stays on full bore ( you'll notice I have one dead lamp). I think I'm going to wait for my deoxit to arrive tomorrow then move onto bypassing the switch if that doesn't work.

IMG_20180925_125806.jpg

Anyway, thanks for all the help and suggestions, turns out I'm just a n00b.
 
After I posted I actually ended up removing the switch assembly from the receiver and taking the cover off. I couldn't see much as the switches appear to be one solid pre-fab assembly soldered to the board, but looking inside the back of the switch it would appear that the switch selector has two metal pins (jumper) making direct contact with the PCB floor. On mine, there were actually grooves worn into the PCB where the metal pins traveled. I imagine that this wear over time would either incorrectly expose traces or wear right thru them over time eventually rendering the switch completely useless as there would no longer be a trace to make contact with or it would always be making contact with metal trace.
 
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