Pioneer SX-650 Going In & Out of Protection

[boreas]

I've only had this one for a month more or less and it hasn't had all that much use but it worked fine until today. Now it goes in and out of protection more or less constantly. When it cuts out it comes back on pretty quickly, anywhere from 2 or 3 to maybe 10 seconds. One oddity that I seem to be seeing, though I haven't really confirmed it is that the problem seems worse (more frequent interruptions) with the A speaker taps than with the B taps.

[EDIT] Switched back to A taps and it's happening less there now too.

Is there anything more likely than another for this particular problem? I'd expect for the receiver to be more likely to go into protection and just stay there or stay there until something or other had cooled.

Thanks!
John

 

[boreas]

I just noticed the other thread about a similar problem on an SX-850. I'll follow that thread as well. Still, any "SX-650-specific" info will be very much appreciated.

So, when I switched back to the A taps it cut out once and hasn't since. Longest interval since the problem first arose.

John

 

[Watthour]

How are the power supply voltages compared to the diagram HERE. Check all the ±50V, ±36V, +30V, and +13V supplies once it is fully warmed.

If you measure the DC voltage at the speaker terminals with the volume fully down (zero) and no input signal - AUX selected with no AUX source connected. How many millivolts are present at each channel?

 

[boreas]

Thanks for your reply!

How are the power supply voltages compared to the diagram HERE. Check all the ±50V, ±36V, +30V, and +13V supplies once it is fully warmed.

I wasn't able to follow that link but it appears to be a link to a download for the SX-650 service manual. I have a copy here if you could point me to a page number. I'd also need instructions as to what to check on the PS board. (I'm pretty green on this sort of thing.)

If you measure the DC voltage at the speaker terminals with the volume fully down (zero) and no input signal - AUX selected with no AUX source connected. How many millivolts are present at each channel?

The voltages there are

L: 35.7mV
R: 51.0mV

By the way, it doesn't seem to want to cut out now with the volume down, no program source selected and no speakers attached. Is that an indication of something specific?

Thanks again!

John

 

[boreas]

By the way, it doesn't seem to want to cut out now with the volume down, no program source selected and no speakers attached. Is that an indication of something specific?

Belay that!

John

 

[boreas]

I just hooked the DMM up to the speaker taps for the right channel and watched to see whether anything like a voltage spike occurred just prior to the relay clicking off. Well, it just drops off to zero when the relay opens and comes back up to 51mV when it comes back on.

John

 

[Watthour]

Yes, that was a link to the service manual at HiFi - You have to log in there to access the manual downloads.

The GWR-101 Board power supplies should be within 10% of the markups on Pg. 66 (referenced to chassis ground). Make sure the 7½VAC supply to Pin 31 is consistent since it also feeds the protection circuit.

 

[blhagstrom]

The SX-650 protection issue is how I found AK.

Get the SM. I have forgotten if the sx-650 is adjustable.
It certainy can't be checked in protection.
Mine ended up being "tired" transistors in the protection circuit.
Here is the thread.

http://www.audiokarma.org/forums/showthread.php?t=264867