[johnnylexus]

I am thinking about opening up my Cary 300SEI in order to tighten the prongs on the headphone input. Another head-fi guy said it was easy to do but that I needed to discharge the caps in the power supply. I have no idea how to do this. I have never opened an amp. Can anybody advise? A photo would really be nice.

p.s.
the only kinds of tools I have are hammers, pliers and screw drivers. lol.

 

[8xOverMsOctober]

Get or make some jumpers to use, then jumper a resistor to the terminals on the caps (you can jumper a screwdriver or two to the resistor and touch the terminals with the screwdriver(s) if you can't clip directly to the terminals). The discharge rate will vary based on the value of the resistor you use. You'll probably want at least a 50 ohm resistor. After you discharge it, check to make sure it's fully discharged with a multimeter/voltmeter. If you don't have one the just leave the resistor in place for like 5 mins - that should be enough time to fully discharge it (so long as you don't use a really high impedance resistor).

Example pic: http://i.ehow.com/images/GlobalPhoto...88606_Full.jpg

 

[applegd]

jumper cable has a resistor and LED to the terminals on the caps...

when the LED goes from ON to off, you know it is discharged.

 

[8xOverMsOctober]

Quote:

Originally Posted by applegd /img/forum/go_quote.gif jumper cable has a resistor and LED to the terminals on the caps... when the LED goes from ON to off, you know it is discharged.

Not necessarily...

LEDs usually have around a 1.2-1.5 volt min operating voltage. So when the LED goes off then you only know that you've dropped below approximately 1 volt or so. Some LEDs might stay lit for longer, but there could still possibly be a charge even when the LED goes out.

So you'll probably want to have that configuration hooked up for a little extra time.

And, as always, test the cap after you discharge it to make sure it's fully discharged.

 

[johnnylexus]

thanks for the reply. i think i better avoid this as I don't own any jumpers or resistors

 

[Tridacnid]

Radio Shack has 'em for cheap.

 

[SiBurning]

Might as well just let it sit for a few days and be really careful not to touch anything. I did some calculations and it looks like you need a 2W 100k-ohm resistor, or a 20W 10k-ohm resistor. I'd get two 100k-ohm resistors and leave them there for 3 hours. Of course, this is using the most conservative numbers and worst case conditions. Personally, I'd knock those number way down and do it in stages with different resistors until I got to straight wire.

 

[applegd]

Quote:

Originally Posted by 8xOverMsOctober /img/forum/go_quote.gif So you'll probably want to have that configuration hooked up for a little extra time. And, as always, test the cap after you discharge it to make sure it's fully discharged.

Man, we are talking about discharge CAP not BATTERY! After you see LED completely goes off, usually couple(at least 1-2) seconds already pass when you disconnect the jumper cabel. So this is not a problem unless your action is extremely fast...

This is OK if the Capacitance is small.

Quote:

Originally Posted by SiBurning Personally, I'd knock those number way down and do it in stages with different resistors until I got to straight wire. .

This is most secured way if the Capacitance is huge....

 

[johnnylexus]

thanks guys ... I took it into a local hi-fi shop yesterday and they took care of it.

 

[SiBurning]

The real problems here are (1) not really knowing the circuit details, and (2) the person doing this isn't familiar with things. The numbers I see in reviews are 1200 microfarads at 250V. The main danger in using a quick discharge is the involuntary reaction of the unprepared human from the shock or scare. Otherwise, you could unplug the unit and use a screwdriver if your caps can handle the rush current.