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Pioneer sx-680 right meter spikes, large pop in speaker

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Dlrockey76

Active Member
I have a pioneer sx-680 and when ever you turn on or off the power or switch between inputs (not including tape monitors 1 & 2) the right meter peaks for a split second and and hugh pop come thru the right speaker but everything works fine untill I hit power or input selector. Any ideas what it is
 
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If it's the right side only then the Power supply is fine.
The receiver uses the STK-0039 module.
I would measure the voltage on pins 1 and 0 (zero) of the module when turning on or off the receiver. Probably disconnect the speakers or switch them off.
See if there's a voltage spike on those pins.
Also. With the power on and volume at min. No input signals. Measure the voltage on all the module pins and record them for us to see.
There are other checks you can do to verify the receiver minus the modules installed but that can wait. You'll need four 1K resistors to simulate a removed module.
 
zebulon1 said:
If it's the right side only then the Power supply is fine.
The receiver uses the STK-0039 module.
I would measure the voltage on pins 1 and 0 (zero) of the module when turning on or off the receiver. Probably disconnect the speakers or switch them off.
See if there's a voltage spike on those pins.
Also. With the power on and volume at min. No input signals. Measure the voltage on all the module pins and record them for us to see.
There are other checks you can do to verify the receiver minus the modules installed but that can wait. You'll need four 1K resistors to simulate a removed module.
Click to expand...

Ok so I measured the voltage on pin 1 & 0. I did it on the left & right modules. On the good left side no spikes. Pin 1 read o volts, pin 0 read 1.8 volts. On the bad right side pin 1 spiked to 4.5 volts then dropped down to 0 volts. Pin 0 spiked to 7.8 volts then dropped down to 2.1. This is all when turning it on. When turning it off the right side when up and down, up and down, up and down then finally dropped down to 0.
 
On the right channel, take out (desolder and remove) the coupling cap C301 .47/50 and try the same procedure.
This will separate the pre amp from the amp and will isolate the issue.
I'm thinking your going to need some components. Capacitors and a few transistors.
Hopefully not the Jfet.
 
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zebulon1 said:
On the right channel, take out (desolder and remove) the coupling cap C301 .47/50 and try the same procedure.
This will separate the pre amp from the amp and will isolate the issue.
I'm thinking your going to need some components. Capacitors and a few transistors.
Hopefully not the Jfet.
Click to expand...

So I have a downloaded schematic but I cant read the tiny numbers to find c301 but looking at the actual PCB there was 1 Cap with those specs but there wasn't a left & right, just the one. It was the first cap between the preamp board and main board right next to the big filter caps but it's the only one that matched the specs so I removed it and got the exact same readings as before.
 
There maybe a few different versions.
I use the schematics from Rick’s Stereo Manuals and he only has one. (KC) I believe.
 
Yes
It is a .47/50 (C301?) coupling cap, between the pre and the main amp.
Pete is not referring to the correct one.

2sc945 > 512-KSC1845FTA
2sa733 > 512-KSA992FBU
2sc1919 > 512-KSC1845EBU
1S2473 > 512-1N4148
2sc1735 > 512-KSC2383YBU

tempsnip 1.png
 
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'whoops ..sorry about that .. it was late at night .'
The small scat was hard to focus on plus the tiny circuit. I'm with you on this one.

"Dirocky",
Not a bad idea:
You can remove the module and install a 1k ohm resistor between pins 1-3 and pins 8-0.
This would simulate the module and not subdue the old STK to those high voltages. A few more times in checking isn't going to hurt but. I worry a little bit. I think the module is still functional.
 
zebulon1 said:
'whoops ..sorry about that .. it was late at night .'
The small scat was hard to focus on plus the tiny circuit. I'm with you on this one.

"Dirocky",
Not a bad idea:
You can remove the module and install a 1k ohm resistor between pins 1-3 and pins 8-0.
This would simulate the module and not subdue the old STK to those high voltages. A few more times in checking isn't going to hurt but. I worry a little bit. I think the module is still functional.
Click to expand...

I have 1/2 watt resistors. Will that be ok and do I install the resistors on both stk mods or just the bad one (right side) ?
 
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