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Sx-650 going into protection when turning up volume.

prose116

prose116

New Member
I have a Sx-650 I bought 2 months ago, I replaced all the electrolytic capacitors put in new leds and have been using it since with no issues. Now when i turn up the volume past 1/4 it goes into protection, when I turn the volume back down it comes back on. I check voltages on power supply , amp and protection board and they seem normal as per the schematic., I put in a new relay still same issue.
Any insight would be appreciated.
 
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Make damn sure one of your speaker wires is not shorted (or a cooked / shorted woofer voice coil). You can move the balance control from one side to the other to see if it is one channel or the other causing the issue.
 
Both channels work fine until I turn it up and it cuts out.
Speakers and speaker wire is fine.
i have a small collection of pioneers that have no issues using same speakers and wires
Sx-450
Sx-780
Sx-838
Sx-980
 
When you did the recap, did you replace the GWR-101 C21 & C22 ? (vertical board)
0.22uf / 10v sanyo sky blue CSSA troublemakers?
You can remove D7 to test if that stops the fault.

if that stops it, with C21 & C22 new, Q5 or Q6 (2sc1649) is at fault.
I hate to say it, but... ksc1845 if ya got 'em... the 2sc1649 IS a 130v transistor.

You could try using the balance control to see which is the offending channel.
 
Yes C21 and C22 were replaced when I did the recap, I lifted 1 leg of D7 and still same issue.
Tried balance control, both channels work until I go up past 1/4 volume then they both cut out.
 
ok, as a test, lift 1 leg each of D8 &D9 and see if that suppresses the protection. Leave D7 open for now please.

also for giggles, check the +33v regulated at R41 or R42 (15k) ,
and the -34v regulated supply at H or R37 (20k) right near to them.
 
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R37 minus 36.41 i hope...

Ok it is the DC detect. Check C26 & C27, make sure the minuses are connected, and alone - no other connections.

Reconnect D8 & D9.

Sounds like a fault in one of the amps, try lifting a leg of R31(L) and R32(R) (both are 47k) alternately. Then both at once.

I dumbly left out a question before: with or without a speaker load? Can this happen when NO load - speakers or anything - is connected.
(I know, I did ask the balance control question, but no load vs balance control is a whole different kettle of fish)
 
I would look at the DC level on the output, as you turn the volume up (before the relay). Possibly a soft power supply rail (due to a bad capacitor, poor connection, weak rectifier, or something), is causing an offset when the supply is called on to supply current. If you get a large DC offset drift when turning the volume up, look for one of the rails dropping more than the other when the volume is turned up.
 
Re soldered C26 and C27, they looked a little rough, my fault.
reconnect D8 and D9
Lifted leg on R35 no issues re soldered leg
Lifted Leg on R32 no issues
Lifted both legs no issues

put back D7 to test with no load and no issues, Connected speakers and issue returned.
Disconnected D7 and works fine no issue
I looked at components connected to D7 and found the 2 2sc1649 are 25c1845 maybe a error in the schematic?
 
I would check at pins 1 and 5 on the SP-40W output modules, and see if the + or - power supply rail is "sagging" really bad when you turn the volume up with a load. That could cause an offset on both channels that could trip protect. If that does occur, follow the circuit back to the bridge rectifier and main filters, to see where it is getting lost.
 
Pin 1 on both modules starts at 36.6 as the volume goes up they drop to around 35.4 then it cuts out
Pin 5 is the same just -36.6 down to -35.4
 
prose116 said:
reconnect D8 and D9
Lifted leg on R35 no issues re soldered leg
Lifted Leg on R32 no issues
Lifted both legs no issues

put back D7 to test with no load and no issues, Connected speakers and issue returned.
Disconnected D7 and works fine no issue
I looked at components connected to D7 and found the 2 2sc1649 are 25c1845 maybe a error in the schematic?
Click to expand...

Hmmm 25c1845, is there a typo here???

2sc1845 are newer, valid replacements. are you sure they are not KSC1845 ? With KSC1845's we can be SURE they are NOT some crap assed eBay china counterfeits.

Do you have some ksc1845's??

The BOLDED elements PROVE that the overload detectors DON'T LIKE the speakers.

Either the speakers are too low of an impedance, or the overload detectors are borked. Counterfeits can do that.

Which components (if any) of the overload detectors have you changed?
 
I do have ksc1845, The ones in there say c1845, i Can swap them out
I have Polk audio Monitors bookshelf and and a old pair Heathkit speakers, both I use with no issues. It happens on both sets of speakers
The only thing I have done is the electrolytic caps, Nichicon, and I replaced the relay when the issue stated happening
 
Yes, swap out to your c1845's.

When you replaced C21 & C22 what was the part number you used?
 
When you replaced C21 & C22 what was the part number you used?

mouser or whomever's part number.

like 505-MKS2C032201B00KO
 
Replaced the 2 transistors with ksc1845
Caps part number Digi key 493-10948-1-ND
No change after replacing transistors
 
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