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Solid State Safety Question

Panamafred

Panamafred

AK Subscriber
Subscriber
So I'm about to get going on replacing the transistors and capacitors on my Pioneer SX-737. Question is, are there any safety considerations I need to be aware of?

After having it unplugged for a while, my screw driver grazed one of the big capacitors and some sparks flew. What else is going to have stored electricity even after it's unplugged? Is there a way to discharge this electricity besides electrocuting myself?

I was also thinking of turning the unit on after every three or four replaced components to double check my work, is this not a viable strategy? Thanks for any help, my order from mouser should be here soon!
 
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Also, don't solder while in the bathtub.

But seriously, if you are worried about it bleed the caps down with a resistor. You can always check their voltage with your MM before you go in. Make the resistor is big enough. Use the equation P=V^2/R, where P is the power rating of the resistor, V is the voltage on the cap and R is the resistor value.

I doubt there's enough capacitance in a 737 to electrocute a baby mouse though.

I worry more about carcinogenic fumes from the flux than electrocution. Make sure you work in a ventilated area is my advice (that I never follow).
 
Most SS receivers will discharge the main filter caps when they're switched off or unplugged for a few seconds. The power amp section will just keep drawing current from the filter caps until the rail voltage falls to 5V or less which is not dangerous. This usually takes less than 30 seconds. It could take longer, say if the output transistor bias current was set to zero or if the amplifier section was disconnected for some reason.

Absolute safest approach is:
1- Unplug from the wall.
2- Power switch on, just in case the power switch disconnects the amp section from the filter caps (unusual) this ensures it stays connected so the caps can drain.
3- Wait 30 seconds. This is a good time to double check step 1. Got an unswitched outlet on the back of the receiver? Plug in some Christmas lights so it's obvious when the thing is energized.
4- Verify with DMM that near-zero DC voltage is present at main filter caps.

Good luck!
 
these are a lot of good suggestions, thanks a lot guys!

I can't imagine even thinking of starting a project like this without this forum.


Rock and Roll will never die! :guitar:
 
When reinstalling the Caps, Do add in a ..wire wound.. bleeder resistor (a few ohms) across each cap terminal as well as a bypass cap.
The resultant inductance adds a wee bit of sweetness.
True, proven and used in a few Well designed (recent) amps.
Amp design has advanced .. some )
 
bare said:
When reinstalling the Caps, Do add in a ..wire wound.. bleeder resistor (a few ohms) across each cap terminal as well as a bypass cap.
The resultant inductance adds a wee bit of sweetness.
True, proven and used in a few Well designed (recent) amps.
Amp design has advanced .. some )
Click to expand...

More like a few thousand ohms...this needs to be carefully calculated taking into account the initial charge voltage and the safe target voltage you want to discharge to after you turn off your component, along with the time you want to reach that target voltage.
Google it up online, you'll find a calculator at Digi-Key expressly for this purpose.
 
Originally Posted by bare View Post
When reinstalling the Caps, Do add in a ..wire wound.. bleeder resistor (a few ohms) across each cap terminal as well as a bypass cap.
The resultant inductance adds a wee bit of sweetness.
True, proven and used in a few Well designed (recent) amps.
Amp design has advanced .. some )
More like a few thousand ohms...this needs to be carefully calculated taking into account the initial charge voltage and the safe target voltage you want to discharge to after you turn off your component, along with the time you want to reach that target voltage.
Google it up online, you'll find a calculator at Digi-Key expressly for this purpose.
__________________
Click to expand...

Thanks but that is just a little beyond me at this point! :arrow:
 
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