Receiver Capacitors

Hi everyone,

Please let me start by saying I did a large google search followed by a small search on this forum and wasn't able to find an answer to my exact problem. I found bits and pieces but wanted to be sure I got the entire picture so I don't end up on my ass.

My receiver for my stereo system is about 30 years old. The speakers fade in and out on all channels and after a google search I figured I should check the capacitors. Turns out that there are a few that have leaked their internal goo all over the board. It seems pretty straight forward on how to replace them so I figured I would give it a try. After my search today, I realized that capacitors hold a charge after unplugging the item. I also found a few unclear videos that seem to state you can discharge with a multimeter.

My questions are...

A) would a capacitor still be holding a charge if it is blown to the point that it is leaking that goo?

B) Does anybody know of an easy and safe way to discharge without a special discharge pen or resistor. I don't have easy access to either of those things and was hoping not to have to put another order into amazon. I have a multimeter but it's somewhat basic and only has about 5 or 6 options as opposed to some of the other ones I've been seeing people use.

There are two specific capacitors that I am trying to replace. The specs on those capacitors are 8200 uf, 75v, 85 degrees C and 1000 uf, 35v, 85 degrees C.

Any help is much appreciated.

Thanks!

Xero14 said:

Hi everyone,

Please let me start by saying I did a large google search followed by a small search on this forum and wasn't able to find an answer to my exact problem. I found bits and pieces but wanted to be sure I got the entire picture so I don't end up on my ass.

My receiver for my stereo system is about 30 years old. The speakers fade in and out on all channels and after a google search I figured I should check the capacitors. Turns out that there are a few that have leaked their internal goo all over the board. It seems pretty straight forward on how to replace them so I figured I would give it a try. After my search today, I realized that capacitors hold a charge after unplugging the item. I also found a few unclear videos that seem to state you can discharge with a multimeter.

My questions are...

A) would a capacitor still be holding a charge if it is blown to the point that it is leaking that goo?

Click to expand...

Very unlikely

B) Does anybody know of an easy and safe way to discharge without a special discharge pen or resistor. I don't have easy access to either of those things and was hoping not to have to put another order into amazon. I have a multimeter but it's somewhat basic and only has about 5 or 6 options as opposed to some of the other ones I've been seeing people use.

Click to expand...

Use a resistor. 1000 ohm or almost anything will do. Yes, your multi-meter will discharge them too.

John

Xero14 said:

Does anybody know of an easy and safe way to discharge

Click to expand...

I use a screwdriver or any metal tool. Probably not real safe but have never been shocked. Safe if you don't touch the leads with you hand.
I like the meter idea. That way you know if there was a charge and when it is gone.

I don't want to understate the real dangers of capacitors in high voltage systems, but you seem to be way over-thinking this.

In this case, I suggest that you approach the problem like this:

1 Switch off and disconnect from the mains supply.
2 Use your multimeter to measure the voltage on the capacitors.
3 If there is a significant voltage (greater than 1 volt) on the capacitors, discharge them.
4 You can use a screwdriver to discharge the capacitors. This can crack and spit and spark a bit and make a mess of your best screwdriver.
5 Or you can use a low value resistor, say 100 Ohm to 1 K Ohm to do the discharging, much less dramatic than the screwdriver.
6 Don't be surprised that once discharged, the capacitors magically charge themselves back up to a few volts. This is just the capacitor dielectric releasing internally stored energy.
7 Discharge again of you are worried about point 6.
8 Have a look at the capacitors, some designers will put a resistor across the capacitor to ensure that it discharges anyway, often the circuit which is being powered by the capacitors will discharge them to a safe level as power source is switched off.

JimB

Xero14 said:

8200 uf, 75v, 85 degrees C and 1000 uf, 35v, 85 degrees C.

Click to expand...

If you attach a picture of the capacitor we might know where to get them.
Screw terminals?
Solder into a PCB?
Distance from pin to pin?

I've replaced zillions of capacitors, and unless they're from an high-voltage section (mains power, vacuum tube circuit, etc), I don't even bother thinking about discharging them. Technically, I realize this is incorrect, but as a practical matter, it's completely fine. As stated by JimB, dielectric soak can makes the practice meaningless anyway.

Go for 105C rated caps rather than 85C. The price difference is minimal.

alec_t said:

Go for 105C rated caps rather than 85C. The price difference is minimal.

Click to expand...

Except for large values and high voltages, where often 105 degree isn't available.

And while I always use 105 degree (where possible) it only really matters for switch-mode and other high frequency use.

Thanks for the help guys. I got the old ones out fine. I replaced the capacitors and the fuse blew as soon as I turned the receiver back on. I'm not really sure what I did wrong as my soldering looks ok and I put the capacitors in the way they are supposed to go.

Anyway I'm not very tech savvy so I'm just giving up on it lol. I appreciate all of the quick responses.

Cheers!

ronsimpson said:

I use a screwdriver or any metal tool. Probably not real safe but have never been shocked. Safe if you don't touch the leads with you hand.
I like the meter idea. That way you know if there was a charge and when it is gone.

Click to expand...

unless you use a DMM, which has a 10Meg input impedance.... you'll be waiting a long time for the caps to discharge. a screwdriver if you don't have any better way... i use a 10K 5 watt resistor and clip leads... i keep the resistor around for just such a purpose.

if you look at the schematic, sometimes they have bleeder resistors built-in, sometimes not. i always measure the residual voltage before deciding they have to be discharged.