Receiver Capacitors

[Xero14]

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!

 

[jpanhalt]

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?

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.

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

John

 

[ronsimpson]

Does anybody know of an easy and safe way to discharge

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.

 

[JimB]

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

 

[ronsimpson]

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

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?

 

[hyedenny]

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.

 

[alec_t]

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

 

[Nigel Goodwin]

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

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.

 

[Xero14]

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!

 

[unclejed613]

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.

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.